Rocks and Minerals

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ROCKS AND MINERALS

ROCKS AND MINERALS

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Rocks and Minerals

Contents PHOTOGRAPH ON PAGE 1A stone with a blue opal in itscenter is a product of time, sinceit forms over millions of years.

Dynamics of the Earth's Crust

Formation andTransformationof RocksPage 40

Use of Rocksand MineralsPage 76

MineralsPage 18

Classes of RocksPage 60

Rocks, like airplane flight recorders,store in their interior very usefulinformation about what has

happened in the past. Whether formingcaves in the middle of mountains, mixedamong folds, or lying at the bottom oflakes and oceans, stones are everywhere,and they hold clues to the past. Bystudying rocks, we can reconstruct thehistory of the Earth. Even the mostinsignificant rocks can tell stories aboutother times, because rocks have beenaround since the beginning of the universe.They were part of the cloud of dust andgases that revolved around the Sun overfour billion years ago. Rocks have been

silent witnesses to the cataclysms ourplanet has experienced. They know thecold of the glacial era, the intense heat ofthe Earth's interior, and the fury of theoceans. They store much informationabout how external agents, such as wind,rain, ice, and temperature changes, havebeen altering the planet's surface formillions of years.

For ancient civilizations, stonessymbolized eternity. This idea haspersisted throughout time because

stones endure, but they are recycled timeand again. Fifty million years from now,nothing will be as we now know it—notthe Andes, nor the Himalayas, nor the iceof Antarctica, nor the Sahara Desert.Weathering and erosion, though slow, willnever stop. This should free us from anyillusion of the immortality of the Earth'sfeatures. What will everything be like inthe future? We don't know. The only sure

thing is that there will be rocks. Onlystones will remain, and their chemicalcomposition, shape, and texture willprovide clues about previous geologicalevents and about what the Earth's surfacewas like in the past. In the pages of thisbook, illustrated with stunning images, youwill find invaluable information about thelanguage of rocks and natural forces ingeneral. You will also learn to identify themost important minerals, know theirphysical and chemical properties, anddiscover the environments in which theyform.

Did you know that the Earth's crustand its oceans are sources of usefuland essential minerals for human

beings? Coal, petroleum, and natural gasfound in the crust allow us to travel and toheat our homes. Furthermore, practically allthe products that surround us haveelements provided by rocks and minerals.For example, aluminum is used to producebeverage cans; copper is used in electriccables; and titanium, mixed with otherdurable metals, is used in the constructionof spacecraft. We invite you to enjoy thisbook. It is full of interesting and worthwhileinformation. Don't miss out on it!

Memory ofthe Planet

THE MONK'S HOUSEThis orthodox monk lives in avolcanic cave, very close to the11 Christian churches located inthe Ethiopian town of Lalibela.

Dynamics of the Earth's Crust

The Earth is like a blender inwhich rocks are moved around,broken, and crumbled. Thefragments are deposited,forming different layers. Then

weathering and erosion by wind and rainwear down and transform the rock. Thisproduces mountains, cliffs, and sanddunes, among other features. Thedeposited material settles into layers of

sediment that eventually becomesedimentary rock. This rock cycle neverstops. In 50 million years, no singlemountain we know will exist in the samecondition as it does today.

TRAVERSING TIME 8-11

UNDER CONSTRUCTION 12-13

A CHANGING SURFACE 14-15

BEFORE ROCK, MINERAL 16-17

MOUNTAINS OF SANDCorkscrew Canyon in Arizonacontains an array of shapes, colors,and textures. The sand varies frompink to yellow to red depending onthe sunlight it receives.

ClimateConsolidationbegins under arain of meteors.

The Earth coolsand the firstocean is formed.

The oldestminerals, such aszircon, form.

The oldest rocksmetamorphose,forming gneiss.

1,100Rodinia, an earlysupercontinent,forms.

A meteorite falls inSudbury, Ontario,Canada.

542The supercontinentPanotia forms, containingportions of present-daycontinents. North Americaseparates from Panotia.

Laurentia andBaltica converge,creating theCaledonian range.Gneiss forms onthe coast ofScotland.

The region that willbecome North Americamoves toward theEquator, thus initiatingthe development of themost importantcarboniferous formations.Gondwana moves slowly;the ocean floor spreadsat a similar speed.

The fragments ofcontinents combine toform a single continentcalled Pangea.

The AppalachianMountains form.The formation of slatethrough sedimentation isat its peak.

Baltica and Siberiaclash, forming the UralMountains.

Eruptions of basaltoccur in Siberia.

The first majororogeny(Caledonianfolding) begins.Gondwana movestoward the SouthPole.

Temperatures fall.The level of carbondioxide (CO2) in theatmosphere is 16times higher than itis today.

The largest carbondeposits we observetoday form whereforests previouslyexisted.

Amphibians diversifyand reptiles originatefrom one amphibiangroup to become thefirst amniotes. Wingedinsects such asdragonflies emerge.

Palm trees andconifers replace thevegetation from theCarboniferous Period.

800 Second glaciation

600 Last massive glaciation

2,500Glaciations: White EarthThe Earth undergoes the first of itsmassive global cooling events(glaciations).

Temperatures weretypically warmer thantoday, and oxygen(O2) levels attainedtheir maximum.

ERAPERIOD

Hadean

Pregeologic

EPOCH

4,600Proterozoic

Precambrian

2,500Paleozoic THE ERA OF PRIMITIVE LIFE

Cambrian

542

Ordovician

488.3

Silurian

443.7

Devonian

416

Carboniferous

359.2

Permian

299Age in millionsof years

OROGENIES Geological history recognizes long periods (lastingmillions of years) of intense mountain formationcalled orogenies. Each orogeny is characterized byits own particular materials and location.

The rocks of this periodcontain an abundanceof fish fossils.

Areas of solid groundare populated bygigantic ferns.

TRILOBITESMarine arthropodswith mineralizedexoskeletons

SILURIANOne of the firstpisciform vertebrates,an armored fishwithout mandibles

It is thought that theEarth's atmospherecontained far less carbondioxide during theOrdovician than today.Temperatures fluctuatewithin a range similar towhat we experiencetoday.

Na2.8%K

2.6%

Mg2.1%Ca

3.6%

Fe5.0%

Al8.1%

Si27.7%

O46.6%

Life

Hot, humid climatesproduce exuberantforests inswamplands.

By this period,vertebrates withmandibles, such as the placoderms,osteichthyans (bony fish), andacanthodians, have alreadyemerged.

THE COREThe Earth's core isextremely hot andis made mostly ofiron and nickel.

Geologists and paleontologists use many sources to reconstructthe Earth's history. The analysis of rocks, minerals, and fossilsfound on the Earth's surface provides data about the

deepest layers of the planet's crust and reveals both climatic andatmospheric changes that are often associated withcatastrophes. Craters caused by the impact of meteorites andother bodies on the surface of the Earth also reveal valuableinformation about the history of the planet.

Traversing Time

ELEMENTS PRESENT ACCORDING TO THE TABLEExisting in different combinations, the crust of the Earthcontains the same elements today as those that werepresent when the planet was formed. The most abundantelement in the crust is oxygen, which bonds with metalsand nonmetals to form different compounds.

THE CAMBRIAN EXPLOSIONFossils from this time attest tothe great diversity of marineanimals and the emergenceof different types ofskeletal structures, suchas those found in spongesand trilobites.

THE FIRST ANIMALSAmong the most mysterious fossils of thePrecambrian Period are the remains of theEdiacaran fauna, the Earth's first-knownanimals. They lived at the bottom of theocean. Many were round and reminiscent ofjellyfish, while others were flat and sheetlike.

MASS EXTINCTIONNear the end of thePermian Period, anestimated 95 percent ofmarine organisms and overtwo thirds of terrestrialones perish in the greatestknown mass extinction.

ComplexStructure

THE FORMATION OF THE INTERIORCosmic materials began to

accumulate, forming a growing celestialbody, the precursor of the Earth. Hightemperatures combined with gravitycaused the heaviest elements tomigrate to the center of the planetand the lighter ones to move towardthe surface. Under a rain of meteors,the external layers began toconsolidate and form the Earth's crust.In the center, metals such as ironconcentrated into a red-hot nucleus.

8 DYNAMICS OF THE EARTH’S CRUST

Metals

Transition metals

Nonmetals

Noble gases

Lanthanide series

Actinide series

METALLIC COREThe light elementsform the mantle.

COLLISIONAND FUSIONHeavy elementsmigrate.

are external folds of the crustproduced by extremely powerfulforces occurring inside the Earth.

Mountains

1

2 3

Small bodies anddust accumulateto become the sizeof an asteroid.

ROCKS AND MINERALS 9


Mesozoic THE ERA OF REPTILES

Triassic

251Cenozoic THE AGE OF MAMMALS

Paleogene

Paleocene Eocene

65.5Jurassic

199.6

Cretaceous

145.5

Neogene

Miocene

23.03

Pleistocene Holocene

Africa separates from South America,and the South AtlanticOcean appears.

Proliferation ofinsects

Appearance ofdinosaurs

The first mammalsevolve from a groupof reptiles calledTherapsida.

Birds emerge.

The dinosaursundergo adaptiveradiation.

North America andEurope drift apart.North and SouthAmerica are joined atthe end of this timeperiod. The formation ofPatagonia concludes,and an importantoverthrust raises theAndes mountain range.

The heat caused by theexpansion of fragmentsfrom the impact togetherwith the greenhouse effectbrought about by thespreading of ashes in thestratosphere provoked aseries of climatic changes.It is believed that thisprocess resulted in theextinction of the dinosaurs.

The African Rift Zone andthe Red Sea open up. TheIndian protocontinentcollides with Eurasia.

Gondwanareappears.

IMPACT FROM THE OUTSIDE It is believed that a large meteor fell onChicxulub, on the Yucatán Peninsula(Mexico), about 65 million years ago. Theimpact caused an explosion that created acloud of ash mixed with carbon rocks. Whenthe debris fell back to Earth, some expertsbelieve it caused a great global fire.

THE LAST GLACIATIONThe most recent period ofglaciation begins three million yearsago and intensifies at the beginningof the Quaternary period. NorthPole glaciers advance, and much ofthe Northern Hemisphere becomescovered in ice.

HUMAN BEINGS APPEAR ON EARTH.Although the oldest hominid fossils(Sahelanthropus) date back to seven millionyears ago, it is believed that modern humansemerged in Africa at the end of thePleistocene. Humans migrated to Europe100,000 years ago, although settling therewas difficult because of the glacial climate.According to one hypothesis, our ancestorsreached the American continent about10,000 years ago by traveling across thearea now known as the Bering Strait.

FORMATION OFMOUNTAIN CHAINS

Central Rocky Mountains

Alps

Himalayas

603020

CORE

ALLOSAURUSThis carnivoremeasured 39 feet(12 m) long.

MAMMOTHSMammoths lived in Siberia.The cause of their extinctionis still under debate.

Carbon dioxidelevels increase.Averagetemperaturesare higher thantoday.

The level of oxygen(O2) in theatmosphere is muchlower than today.

The globalaveragetemperature isat least 62° F(17° C). The icelayer coveringAntarctica laterthickens.

Temperatures drop to levels similar tothose of today. Thelower temperaturescause forests toshrink and grasslandsto expand.

Vast developmentof feathered birdspecies and

mammals coveredwith long fur

THE AGE OF FLOWERING PLANTSAt the end of the Cretaceous Period,the first angiosperms—plants withprotected seeds, flowers, andfruits—appear.

10 DYNAMICS OF THE EARTH’S CRUST

ANOTHER MASS EXTINCTIONToward the end of the CretaceousPeriod, about 50 percent of existingspecies disappear. The dinosaurs, thelarge marine reptiles (such as thePlesiosaurs), the flying creatures of thatperiod (such as the Pterosaurs), and theammonites (cephalopod mollusks)disappear from the Earth. At thebeginning of the Cenozoic Era, most ofthe habitats of these extinct speciesbegin to be occupied by mammals.

Outer CoreThe outer core is 1,400miles (2,270 km) thickand contains melted iron,nickel, and other minorchemical compounds.

Inner CoreThe inner core has a diameter of 756 miles (1,216 km). It is made ofiron and nickel, which are solidifieddue to their exposure to highpressure and temperature conditions.

Minerals, such as iron and silicates, arewidely spread among the major constituentsof the crust. Only the movements of thecrust on the molten mantle disrupt theirequilibrium.

Elements inEquilibrium

The diameter of the crater produced bythe impact of the meteor on the YucatánPeninsula. It is now buried under almost2 miles (3 km) of limestone.

62 miles (100 km)

CRUSTThe Earth's crust can reacha thickness of up to 6 miles(10 km) at the bottom of theocean and up to 30 miles(50 km) on the continents.

MANTLEThe mantle is 1,800 miles(2,900 km) thick and iscomposed mainly of solidrock. Its temperatureincreases with depth. Anotable component of theupper mantle is theasthenosphere, which issemisolid. In the asthenosphere,superficial rock layers that willeventually form the Earth'scrust are melted.

LITHOSPHEREThe solid rock coatingof the Earth, whichincludes the exterior ofthe mantle

PlioceneOligocene

ROCKS AND MINERALS 1312 DYNAMICS OF THE EARTH’S CRUST

Under ConstructionO

ur planet is not a dead body, complete and unchanging. It is an ever-changing system whoseactivity we experience all the time: volcanoes erupt, earthquakes occur, and new rocksemerge on the Earth's surface. All these phenomena, which originate in the interior of the

planet, are studied in a branch of geology called internal geodynamics. This science analyzesprocesses, such as continental drift and isostatic movement, which originate with themovement of the crust and result in the raising and sinking of large areas. Themovement of the Earth's crust also generates the conditions that form new rocks.This movement affects magmatism (the melting of materials that solidifyto become igneous rocks) and metamorphism (the series oftransformations occurring in solid materials that give rise tometamorphic rocks).

MagmatismMagma is produced when the temperature in the mantle or crust reaches a level atwhich minerals with the lowest fusion point begin to melt. Because magma is less

dense than the solid material surrounding it, it rises, and in so doing it cools and begins tocrystallize. When this process occurs in the interior of the crust, plutonic or intrusiverocks, such as granite, are produced. If this process takes place on the outside, volcanicor effusive rocks, such as basalt, are formed.

INNERCRUSTPlutonicRocks

OUTERCRUSTVolcanicrocks

MetamorphismAn increase in pressure and/or temperature causesrocks to become plastic and their minerals to

become unstable. These rocks then chemically react withthe substances surrounding them, creating differentchemical combinations and thus causing new rocks toform. These rocks are called metamorphic rocks. Examplesof this type of rock are marble, quartzite, and gneiss.

FoldingAlthough solid, the materials forming the Earth'scrust are elastic. The powerful forces of the Earth

place stress upon the materials and create folds in therock. When this happens, the ground rises and sinks. Whenthis activity occurs on a large scale, it can create mountainranges or chains. This activity typically occurs in thesubduction zones.

FractureWhen the forces acting upon rocks become too intense,the rocks lose their plasticity and break, creating two

types of fractures: joints and faults. When this process happenstoo abruptly, earthquakes occur. Joints are fissures and cracks,whereas faults are fractures in which blocks are displacedparallel to a fracture plane.

FOLDSFor folds to form, rocksmust be relativelyplastic and be actedupon by a force.

RUPTUREWhen rocksrupture quickly, anearthquake occurs.

OceanicPlate

MagmaticChamber

Asthenosphere

Crust

ConvectiveCurrents

PRESSUREThis force gives rise to newmetamorphic rocks, as olderrocks fuse with the mineralsthat surround them.

TEMPERATUREHigh temperatures makethe rocks plastic andtheir minerals unstable.

Zone ofSubduction62 miles

(100 km)

SeaLevel

124 miles(200 km)

KILAUEA CRATERHawaii

Latitude 19° NLongitude 155° W


A Changing SurfaceT

he molding of the Earth's crust is the product of two great destructive forces: weathering anderosion. Through the combination of these processes, rocks merge, disintegrate, and joinagain. Living organisms, especially plant roots and digging animals, cooperate with

these geologic processes. Once the structure of the mineralsthat make up a rock is disrupted, the mineralsdisintegrate and fall to the mercy of therain and wind, which erode them.

WeatheringMechanical agents can disintegrate rocks, andchemical agents can decompose them. Disintegration

and decomposition can result from the actions of plantroots, heat, cold, wind, and acid rain. The breaking down ofrock is a slow but inexorable process.

WATERIn a liquid or frozen state,water penetrates into therock fissures, causing themto expand and shatter.

A variety of forces can cause rockfragments to break into smallerpieces, either by acting on the rocksdirectly or by transporting rockfragments that chip away at the rocksurface.

MECHANICAL PROCESSES

ErosionExternal agents, such as water, wind, air, and livingbeings, either acting separately or together, wear

down, and their loose fragments may be transported.This process is known as erosion. In dry regions, thewind transports grains of sand that strike andpolish exposed rocks. On the coast, waveaction slowly eats away at the rocks.

In this process, materialseroded by the wind or waterare carried away anddeposited at lower elevations,and these new deposits canlater turn into other rocks.

EOLIANPROCESSESThe wind drags small particlesagainst the rocks. This wears themdown and produces new depositsof either loess or sand dependingon the size of the particle.

CORKSCREWCANYONArizona

Latitude 36° 30´ NLongitude 111° 24´ W

CHEMICALPROCESSESThe mineral componentsof rocks are altered.They either become newminerals or are releasedin solution.

TEMPERATUREWhen the temperature of theair changes significantly over afew hours, it causes rocks toexpand and contract abruptly.The daily repetition of thisphenomenon can cause rocks

to rupture.

Transportation andSedimentation

Cave

Watercurrent

Limestone

River

HYDROLOGIC PROCESSESAll types of moving water slowly weardown rock surfaces and carry looseparticles away. The size of the particles thatare carried away from the rock surfacedepends on the volume and speed of theflowing water. High-volume and high-velocity water can move larger particles.

Wind


Before Rock, MineralT

he planet on which we live can be seen as a large rock or, more precisely, as alarge sphere composed of many types of rocks. These rocks are composed oftiny fragments of one or more materials. These materials are minerals, which

result from the interaction of different chemical elements, each of which is stableonly under specific conditions of pressure and temperature. Both rocks andminerals are studied in the branches of geologycalled petrology and mineralogy.

rock batholiths formed during aperiod of great volcanic activityand created the Torres del Paineand its high mountains.

12 millionyears ago

From Minerals to RocksFrom a chemical perspective, a mineral is ahomogeneous substance. A rock, on the other

hand, is composed of different chemical substances,which, in turn, are components of minerals. Themineral components of rocks are also those ofmountains. Thus, according to this perspective, it ispossible to distinguish between rocks and minerals.

TORRES DEL PAINEChilean Patagonia

Latitude 52° 20´ SLongitude 71° 55´ W

Composition

Highest summit

Surface

Granite

Paine Grande (10,000 feet [3,050 m])

598 acres (242 ha)

Torres del Paine National Park is located in Chilebetween the massif of the Andes and the Patagoniansteppes.

Temperature and pressure play a prominent part in rocktransformation. Inside the Earth, liquid magma is produced.When it reaches the surface, it solidifies. A similar processhappens to water when it freezes upon reaching 32° F (0° C).

CHANGE OF STATE

QUARTZComposed of silica,quartz gives rock awhite color.

FELDSPARA light-coloredsilicate, feldsparmakes up a largepart of the crust.

GRANITERock composed offeldspar, quartz, andmica

MICAComposed ofthin, shinysheets of silicon,aluminum, potassium,and other minerals, micacan be black or colorless.

Minerals

Dallol is basically a desert ofminerals whose ivory-colored crust is scatteredwith green ponds andtowers of sulfur salts in

shades of orange. Some mineralsbelong to a very special class.Known as gems, they are sought andhoarded for their great beauty. Themost valuable gems are diamonds.

Did you know it took human beingsthousands of years to separate metalfrom rock? Did you also know thatcertain nonmetallic minerals arevalued for their usefulness?

Graphite, for instance, is used tomake pencils; gypsum is used inconstruction; and halite, also knownas salt, is used in cooking.

YOU ARE WHAT YOU HAVE 20-21

A QUESTION OF STYLE 22-23

HOW TO RECOGNIZE MINERALS 24-25

A DESERT OF MINERALS 26-27

THE ESSENCE OF CRYSTALS 28-29

DALLOL VOLCANOLocated in Ethiopia, Dallol is the only non-oceanic volcano on Earth below sea level,making it one of the hottest places on theplanet. Sulfur and other minerals that springfrom this volcano create very vivid colors.

CRYSTALLINE SYMMETRY 30-31

PRECIOUS CRYSTALS 32-33

DIAMONDS IN HISTORY 34-35

THE MOST COMMON MINERALS 36-37

THE NONSILICATES 38-39

112elementslisted in theperiodic table.

MINERALSCOME FROM

Components The basic components of minerals are thechemical elements listed on the periodic

table. Minerals are classified as native if they arefound in isolation, contain only one element, andoccur in their purest state. On the other hand, theyare classified as compound if they are composed oftwo or more elements. Most minerals fall into thecompound category.

NATIVE MINERALSThese minerals are classified into:

GOLDAn excellent thermal and electrical conductor.Acids have little or no effect on it.

A- METALS AND INTERMETALSNative minerals have high thermal and electricalconductivity, a typically metallic luster, lowhardness, ductility, and malleability. They are easyto identify and include gold, copper, and lead.

B- SEMIMETALS Native minerals that are morefragile than metals and havea lower conductivity.Examples are arsenic,antimony, and bismuth.

C- NONMETALS An important group ofminerals, which includessulfur

Isotypic MineralsIsomorphism happens when minerals with the same structure, such as halite and galena,exchange cations. The structure remains the same, but the resulting substance is different,

because one ion has been exchanged for another. An example of this process is siderite (rhombicFeCO3), which gradually changes to magnesite (MgCO3) when it trades its iron (Fe) for similarly-sized magnesium (Mg). Because the ions are the same size, the structure remains unchanged.

PolymorphismA phenomenon in which the samechemical composition can create

multiple structures and, consequently,result in the creation of several differentminerals. The transition of onepolymorphous variant into another,facilitated by temperature or pressureconditions, can be fast or slow and eitherreversible or irreversible.

types ofminerals

have been recognized by theInternational Association of Mineralogy.

MORE THAN

ChemicalComposition

CaCO3

CaCO3

FeS2

FeS2

C

C

CrystallizationSystem

Mineral

Calcite

Aragonite

Pyrite

Marcasite

Diamond

Graphite

DIAMOND AND GRAPHITEA mineral's internal structure influences its hardness. Bothgraphite and diamond are composed only of carbon; however,they have different degrees of hardness.

Atoms form hexagons thatare strongly interconnectedin parallel sheets. Thisstructure allows the sheetsto slide over one another.

Each atom is joined to four otheratoms of the same type. Thecarbon network extends in threedimensions by means of strongcovalent bonds. This provides themineral with an almostunbreakable hardness.

Diamond Graphite

Trigonal

Rhombic

Cubic

Rhombic

Cubic

Hexagonal

Model demonstratinghow one atom bondsto the other four

Hardness of 10on the Mohs scale

Halite NaCl Galena PbSCl Na S Pb

HALITE AND GALENA

Hardness of 1on the Mohs scale

Cubic InternalStructure

CarbonAtom

SILVERThe close-upimage shows thedendrites formed bythe stacking ofoctahedrons, sometimes inan elongated form.

Microphotograph ofsilver crystal dendrites

SULFURBISMUTH

HALITEis composed ofchlorine and sodium.

1

2 COMPOUNDMINERALSCompound mineralsare created whenchemical bonds formbetween atoms ofmore than one element.The properties of acompound mineral differfrom those of itsconstituent elements.

Minerals are the “bricks” of materials that make up theEarth and all other solid bodies in the universe. They areusually defined both by their chemical composition and by

their orderly internal structure. Most are solid crystallinesubstances. However, some minerals have a disordered internalstructure and are simply amorphous solids similar to glass.Studying minerals helps us to understand the origin of the Earth.Minerals are classified according to their composition andinternal structure, as well as by the properties of hardness,weight, color, luster, and transparency. Although more than4,000 minerals have been discovered, only about 30 arecommon on the Earth's surface.

You Are What You Have

20 MINERALS ROCKS AND MINERALS 21

4,000

22 MINERALS

A Question of StyleO

ptical properties involve a mineral's response to the presence of light. Thischaracteristic can be analyzed under a petrographic microscope, whichdiffers from ordinary microscopes in that it has two devices that polarize

light. This feature makes it possible to determine some of the optical responses ofthe mineral. However, the most precise way to identify a mineral by its opticalproperties is to use an X-ray diffractometer.

EXOTIC COLOR

QUARTZ

ROCK CRYSTALColorless; the pureststate of quartz

SMOKYDark, brown, or gray minerals

CITRINEThe presence of iron producesa very pale yellow color.

AMETHYSTThe presence of iron in aferric state results in apurple color.

ROSEThe presence of manganeseresults in a pink color.

Refraction and Luster

Refraction is related to the speedwith which light moves through a

crystal. Depending on how light propagatesthrough them, minerals can be classified asmonorefringent or birefringent. Lusterresults from reflection and refraction oflight on the surface of a mineral. In general,it depends on the index of refraction of amineral's surface, the absorption of incidentlight, and other factors, such as concretecharacteristics of the observed surface (forinstance, degree of smoothness and polish).Based on their luster, minerals can bedivided into three categories.

METALLICMinerals in this class arecompletely opaque, acharacteristic typical of nativeelements, such as copper, andsulfides, such as galena.

SUBMETALLICMinerals in this class havea luster that is neithermetallic nor nonmetallic.

NONMETALLICMinerals in this classtransmit light when cutinto very thin sheets. Theycan have several types ofluster: vitreous (quartz),pearlescent, silky (talc),resinous, or earthy.

Coloris one of the most striking properties ofminerals. However, in determining the

identity of a mineral, color is not always useful.Some minerals never change color; they are calledidiochromatic. Others whose colors are variable arecalled allochromatic. A mineral's color changes canbe related, among other things, to the presence ofimpurities or inclusions (solid bodies) inside of it.

Streakis the color of a mineral'sfine powder, which can beused to identify it.

Some mineralsalways have thesame color; oneexample ismalachite.

INHERENTCOLOR

A mineral can have severalshades, depending on itsimpurities or inclusions.

LuminescenceCertain minerals emit light whenthey are exposed to particular

sources of energy. A mineral is fluorescentif it lights up when exposed to ultravioletrays or X-rays. It is phosphorescent if itkeeps glowing after the energy source isremoved. Some minerals will also respondto cathode rays, ordinary light, heat, orother electric currents.

MALACHITE SULFUR

Other secondary minerals,known as exotic minerals,are responsible for givingquartz its color; when itlacks exotic minerals,quartz is colorless.

AGATEA type of chalcedony, acryptocrystalline variety ofquartz, of nonuniform coloring

More reliable than a mineral's color is itsstreak (the color of the fine powder leftwhen the mineral is rubbed across a hardwhite surface).

COLOR STREAK

Agates crystallize in bandedpatterns because of theenvironments in which theyform. They fill the cavities ofrocks by precipitating out ofaqueous solutions at lowtemperatures. Their colorsreflect the porosity of the stone,its degree of inclusions, and thecrystallization process.

HEMATITEColor: Black

Streak Color: Reddish Brown


ROCKS AND MINERALS 2524 MINERALS

How to Recognize MineralsA

mineral's physical properties are very important for recognizing it at first glance.One physical property is hardness. One mineral is harder than another when theformer can scratch the latter. A mineral's degree of hardness is based on a

scale, ranging from 1 to 10, that was created by German mineralogist FriedrichMohs. Another physical property of a mineral is its tenacity, or cohesion—that is,its degree of resistance to rupture, deformation, or crushing. Yet another ismagnetism, the ability of a mineral to be attracted by a magnet.

Exfoliation and FractureWhen a mineral tends to break along theplanes of weak bonds in its crystalline

structure, it separates into flat sheets parallel toits surface. This is called exfoliation. Minerals thatdo not exfoliate when they break are said toexhibit fracture, which typically occurs in irregularpatterns.

1. TALC is the softestmineral. 2. GYPSUM

can be scratchedby a fingernail. 3. CALCITE

is as hard as abronze coin. 4. FLUORITE

can be scratchedby a knife. 5. APATITE

can be scratchedby a piece of glass. 6. ORTHOCLASE

can be scratchedby a drill bit. 7. QUARTZ

can be scratchedby tempered steel. 8. TOPAZ

can be scratchedwith a steel file. 9. CORUNDUM

can be scratchedonly by diamond. 10. DIAMOND

is the hardestmineral.

TYPES OF EXFOLIATION

Cubic Octahedral Dodecahedral

Rhombohedral Prismatic andPinacoidal

Pinacoidal(Basal)

ranks 10 minerals, from the softest to the hardest. Eachmineral can be scratched by the one that ranks above it.

MOHS SCALE

FRACTUREcan be irregular,conchoidal, smooth,splintery, or earthy.

7 to 7.5IS THE HARDNESS OF THETOURMALINE ON THE MOHS SCALE.

ElectricityGeneration

Piezoelectricity andpyroelectricity are

phenomena exhibited by certaincrystals, such as quartz, whichacquire a polarized chargebecause exposure to temperaturechange or mechanical tensioncreates a difference in electricalpotential at their ends.

PIEZOELECTRICITYThe generation of electric currentsthat can occur when mechanicaltension redistributes the negativeand positive charges in a crystal.Tourmaline is an example.

PYROELECTRICITYThe generation of electric currentsthat can occur when a crystal issubjected to changes intemperature and, consequently,changes in volume.

PRESSURE

Positivecharge

Negativecharge

Positivecharge

Negativecharge

HEAT

IRREGULAR FRACTURE An uneven, splinterymineral surface

TOURMALINEis a mineral of thesilicate group.

COLORSome tourmalinecrystals can havetwo or more colors.

DENSITYreflects the structure andchemical composition of amineral. Gold and platinumare among the most denseminerals.


A Desert of MineralsT

he Dallol region is part of the Afar depression in Ethiopia. It is known as “thedevil's kitchen” because it has the highest average temperature in the world,93° F (34° C). Dallol is basically a desert of minerals with an ivory-colored

crust, sprinkled with green ponds and towers of sulfurous salt, in shades of orange,called hornitos (8 to 10 feet [2.5–3 m] high), many of which are active and spit outboiling water.

ETHIOPIALatitude 9° N

Longitude 39° E

Location

Type of volcano

Elevation

Last eruption

Annual salt extraction

Afar Depression

Explosion Crater

–125 feet (–48 m)

1926

135,000 tons

Salt DepositsHydrothermal activity occurs whenunderground water comes in contact

with volcanic heat. The heat causes thewater to rise at high pressure through layersof salt and sulfur. The water then dissolvesthe salt and sulfur, which precipitate out asthe water cools at the surface. As a result,ponds and hornitos are created. The richnessof their coloring may be explained by theirsulfurous composition and by the presenceof certain bacteria.

There are two types of hornitos:active ones, which forcefullyexpel boiling water, and inactiveones, which simply contain salt.

TYPES OF HORNITOS

ACTIVEIt expels boilingwater, and it isconstantly growing.

INACTIVEComposed of salt, the hornitono longer expels water. It wasactive in the past.

Manual ExtractionSalt is extracted without machinery. Defying the arid climate,inhabitants of the Borena region in southern Ethiopia extract

the mineral by hand for a living. They wear turbans to protectthemselves from the harmful effects of the Sun. Camels then carrythe day's load to the nearest village.

BorenaA Black, Muslim, Afar-speaking ethnic group,whose members extractsalt in the Dallol. TheBorena represent 4percent of the Ethiopianpopulation.

TURBANThis piece of clothingprotects workers from theextreme temperatures ofthe desert and theintensity of the Sun whilethey extract salt.

148,800 tons(135,000 metric tons)per yearAmount of salt obtained manuallyin the Afar (or Danakil) depression

3.3 billion tons(3 billion metric tons)TOTAL RESERVE OF ROCK SALTIN THE AFAR DEPRESSION

DALLOL VOLCANO

8 to 10 feet (2.5-3 m)

high

ETHIOPIA

DALLOL

YEMEN

KENYA

SUDAN

SOMALIA

ERITREA

RedSea

AfarDepress ion

OLD DEPOSITThe dark coloringindicates that this depositis several months old.

PONDBoiling water emergesfrom the hornitos andforms small ponds onthe surface.

OLD,INACTIVEHORNITO

YOUNG,ACTIVEHORNITO

ASCENTThe hot water startsto rise underground.

1

HEATContact with hot rockmaintains the water'stemperature.

2

EXITThe hot water isexpelled throughthe hornito.

3

YOUNG DEPOSITNewer deposits have awhite color, whichbecomes darker over time.

Boilingwater

Hot waterrising fromthe subsoil

OTHER MINERALSIn addition to sulfurs andsulfates, potassiumchloride, an excellent soilfertilizer, is also extractedfrom the Dallol.

HEATVolcanic heatwarms the waterunderground.

1

Water expelled from its magmaticspring erupts, surfacing as thermalwater. When the water evaporates,salt deposits are formed.

MINERALIZATION PROCESS

ASCENTWater rises to thesurface throughlayers of salt andsulfur deposits.

2

HEATThe heat causes thewater to evaporate.Salt deposits formon the surface.

3

When its exterioris dark, a hornito isseveral months old.

CROSS SECTION

Dallol is located at 125 feet(48 m) below sea level.

Sea Level

RROCKS AND MINERALS 2928 MINERALS

The Essence of CrystalsA

ll minerals take on a crystalline structure as they form.Most crystals originate when molten rock from insidethe Earth cools and hardens. Crystallography is the

branch of science that studies the growth, shape, andgeometric characteristics of crystals. The arrangement ofatoms in a crystal can be determined using X-raydiffraction. The relationship between chemicalcomposition of the crystal, arrangement of atoms, andbond strengths among atoms is studied in crystallographicchemistry.

CRYSTALS OF COMMON SALTWhen salt forms larger crystals,their shape can be seen under amicroscope.

CUBIC STRUCTUREis created through thespatial equilibrium betweendifferent ions, which attracteach other, and similar ions,which repel each other.

A crystal's structure is repeated on the inside, even in thearrangement of its smallest parts: chlorine and sodium ions. In thiscase, the electrical forces (attraction among opposite ions andrepulsion among similar ones) form cubes, which creates stability.However, different mineral compositions can take many otherpossible forms.

INTERNAL CRYSTALLINE NETWORK

LEGEND

Chlorine AnionThis nonmetal canonly acquire amaximum negativecharge of 1.

Sodium CationThis metal canonly acquire amaximum positivecharge of 1.

CUBESalt (Halite)1 chlorine atom +1 sodium atom

BASIC FORMS OF ATOMIC BONDINGThis graphic represents an atom's internalcrystalline network.

TETRAHEDRONSilica1 silicon atom + 4 oxygen atoms

DIFFERENCES BETWEEN CRYSTAL AND GLASSGlass is an amorphous solid. Because it solidifies quickly, theparticles lose mobility before organizing themselves.

ATOMIC MODEL OF ACRYSTALThe particles combineslowly in regular, stableshapes.

7CrystallineSystems

ATOMIC MODEL OF GLASSSolidification prevents theparticles from organizingthemselves. This makes thestructure irregular.

This type of bond occurs between two nonmetallicelements, such as nitrogen and oxygen. The atoms aregeometrically organized to share electrons from their outershells. This way, the whole structure becomes more stable.

COVALENT BOND

Typical of metallic elements that tend to lose electronsin the presence of other atoms with a negative charge.When a chlorine atom captures an electron from asodium atom (metallic), both become electricallycharged and mutually attract each other. The sodiumatom shares an electron (negative charge) andbecomes positively charged, whereas the chlorinecompletes its outer shell, becoming negative.

IONIC BOND

Example: Halite (salt)

SodiumAtom

ChlorineAtom

The sodium atom losesan electron and becomespositively charged.

The anion and the cation (positiveion) are electrically attracted toone another. They bond, forming anew, stable compound.

SodiumAtom

ChlorineAtom

The chlorine atom gains an electron(negative charge) and becomes anegatively charged ion (anion).

Example:Ammonia

BEFOREBONDING

AFTERBONDING

Na Na+

Cl Cl-

HydrogenAtom

NitrogenAtom

The nitrogen atomneeds three electronsto stabilize its outershell; the hydrogenatom needs only one.The union of all fouratoms creates a stablestate.así la logran.

The combination of twoions results in a cubicform. When there aremore than two ions, otherstructures are formed.


Crystalline SymmetryT

here are more than 4,000 minerals on Earth. They appear in nature in two ways: without anidentifiable form or with a definite arrangement of atoms. The external expressions of thesearrangements are called crystals, of which there are 32 classes. Crystals are characterized by

their organized atomic structure, called a crystalline network, built from a fundamental unit (unitcell). These networks can be categorized into the seven crystalline systems according to the crystal'sarrangement. They can also be organized into 14 three-dimensional networks, known as the Bravaislattices.

Typical CharacteristicsA crystal is a homogeneous solidwhose chemical elements exhibit an

organized internal structure. A unit cellrefers to the distribution of atoms ormolecules whose repetition in threedimensions makes up thecrystalline structure. Theexistence of elements withshared symmetry allows the 32crystal classes to be categorizedinto seven groups. These groupsare based on pure geometric shapes,such as cubes, prisms, and pyramids.

Bravais LatticesIn 1850, Auguste Bravaisdemonstrated theoretically

that atoms can be organized intoonly 14 types of three-dimensionalnetworks. These network typesare therefore named after him.

CubicThree crystallographic axesmeet at 90° angles.

Hexagonalprisms have six sides, with 120ºangles. From one end, the crosssection is hexagonal.

MonoclinicPrisms look like tetragonalcrystals cut at an angle.Their axes do not meet at90º angles.

TetragonalThese crystals are shaped likecubes, but one of their facets islonger than the others. All threeaxes meet at 90º angles, but oneaxis is longer than the other two.

TriclinicThese crystals have very oddshapes. They are notsymmetrical from one end tothe other. None of their threeaxes meet at 90º angles.

TrigonalThis system includes the mostcharacteristic rhombohedrons,as well as hexagonal prismsand pyramids. Three equalaxes meet at 120º,with one axismeeting at 90ºto the center.

RhombicThree nonequivalentcrystallographic axesmeet at 90º angles.

THE MOST COMMONSHAPES

Cube

Octahedron

Rhombo-dodecahedron

Tetrahedron

HexagonalPrism

HexagonalBipyramid

HexagonalPrism Combinedwith HexagonalBipyramid

Simple CubicNetwork

Body-centeredCubic Network

Face-centeredCubic Network

PrismsCombinedwith Pinacoids

Prism

HexagonalPrismCombined withBasal Pinacoid

SimpleMonoclinicNetwork

MonoclinicNetworkCentered onits Bases

Only 14 network combinations are possible. THESE COMBINATIONS ARE CALLED BRAVAIS LATTICES.

TetragonalPrism andDitetragonalPrism

TetragonalBipyramid

Prism andBipyramid

SimpleTetragonal

CenteredTetragonal

TriclinicShapes

TriclinicNetwork

TriclinicNetwork

SimpleRhombus

Base-centeredRhombus

CenteredRhombus

Face-centeredRhombus

Pinacoids

Prism andBasalPinacoid

Bipyramid

Prism andDomes

Prisms,Domes, andTwoPinacoids

Trigonal orRhombohedralShapes

TrigonalTrapezohedron

DitrigonalScalenohedron

A crystal's ideal plane of symmetrypasses through its center and divides itinto two equal, symmetrical parts. Itsthree crystallographic axes pass throughits center. A crystal's longest verticalaxis is called “c,” its transverse axis “b,”and its shortest (from front to back) “a.”The angle between c and b is calledalpha; the one between a and c, beta;and the one between a and b, gamma.

CRYSTALSYMMETRY

Vertical Axis

HorizontalPlane Sagittal

Plane

FrontalPlane

Anteroposterior Axis

Transverse Axis

There are sevencrystalline systems.The 32 existing crystal classes aregrouped into these crystalline systems.

LEGEND

CRYSTALLINESYSTEM

BRAVAISLATTICES

CRYSTALLOGRAPHIC

OR COORDINATE AXES

Vanadinite

Brazilianite

Diamond

Scheelite

Labradorite

Rhodochrosite

TopazTRICLINIC7%

RHOMBIC22%

CUBIC12%

TETRAGONAL12%

TRIGONAL9%

HEXAGONAL8%

HOW MINERALSCRYSTALLIZE

MONOCLINIC32%

Precious CrystalsP recious stones are characterized by their beauty, color, transparency, and rarity. Examples are

diamonds, emeralds, rubies, and sapphires. Compared to other gems, semiprecious stones arecomposed of minerals of lesser value. Today diamonds are the most prized gem for their “fire,” luster,

and extreme hardness. The origin of diamonds goes back millions of years, but people began to cut themonly in the 14th century. Most diamond deposits are located in South Africa, Namibia, and Australia.

DiamondMineral composed of crystallized carbon in acubic system. The beauty of its glow is due to a

very high refraction index and the great dispersion oflight in its interior, which creates an array of colors. Itis the hardest of all minerals, and it originatesunderground at great depths.

EXTRACTIONDiamonds are obtained from kimberlitepipes left over from old volcaniceruptions, which brought the diamondsup from great depths.

CUTTING AND CARVINGThe diamond will be cut by another diamondto reach final perfection. This task is carriedout by expert cutters.

2

3

1

B CUTTING: Using a fine steel blade,the diamond is hit with a sharp blow to split it.

A INSPECTION:Exfoliation isdetermined in orderto cut the diamond.

C CARVING: With achisel, hammer,and circular saws,the diamond isshaped.

POLISHINGThe shaping of the facets of the finished gem

BRILLIANCEThe internal faces of thediamond act as mirrorsbecause they are cut at exactangles and proportions.

FIREFlashes of color from a well-cut diamond. Each ray of lightis refracted into the colors ofthe rainbow.

COMMONCUTSA diamond canhave many shapes,as long as itsfacets are carefullycalculated tomaximize itsbrilliance.

GemsMineral, rock, or petrified material that,after being cut and polished, is used in

making jewelry. The cut and number of pieces thatcan be obtained is determined based on theparticular mineral and its crystalline structure.

PRECIOUS STONES SEMIPRECIOUS STONES

DIAMONDThe presence of any color isdue to chemical impurities.

EMERALDChromium gives it itscharacteristic green color.

OPALThis amorphous silicasubstance has many colors.

RUBYIts red color comesfrom chromium.

SAPPHIREBlue to colorless corundum.They can also be yellow.

AMETHYSTQuartz whose color is determinedby manganese and iron

TOPAZA gem of variable color, composedof silicon, aluminum, and fluorine

GARNETA mix of iron, aluminum,magnesium, and vanadium

TURQUOISEAluminum phosphate andgreenish blue copper

THE CHEMISTRY OF DIAMONDSStrongly bonded carbon atoms crystallize in a cubicstructure. Impurities or structural flaws can causediamonds to show a hint of various colors, such asyellow, pink, green, and bluish white.

BRILLIANT EMERALD PRINCESS TRILLION

PEAR HEART OVAL MARQUISE

CROWN13.5334.3°

40.9°

1.9

43.3

BEZEL

STAR

TABLE

GIRDLE

PAVILLION

IDEAL DIAMONDSTRUCTURE

10055.1

MO

UT

HM

AIN

CO

ND

UIT

RO

OT

RING OF WASTEMATERIAL

ERODED LAVA

KKIMBERLEYMINE

COOLEDLAVA

XENOLITHS

PRESSUREZONE

0

0.3 mi(0.5 km)

0.6 mi(1.0 km)

0.9 mi(1.5 km)

1.2 mi(2.0 km)

1.5 mi(2.5 km)

miles(km)

enters the diamond.

The facets of thepavilion reflect the lightamong themselves.

The light is reflectedback to the crown inthe opposite direction.

The rays divideinto theircomponents.

Each color reflectsseparately in thecrown.

LIGHT

LIGHT

0.5 inch(13 mm)

0.3 inch(6.5 mm)

0.08 inch(2 mm)

8 CARATS

6.5 CARATS

0.03 CARAT

27.6 tons(25 metric tons)

1 carat = 0.007 ounce(0.2 grams)

of mineral must be removed toobtain a 1 carat diamond.

320 microns(0.32 mm)

MEASURED VERTICALLY



Diamonds in History

ORIGINAL CUTIt formerly weighed 186carats with 30 facets thatmerged into six facets,which, in turn, becameone. This explains itsname: Mountain of Light.

The Great Koh-i-noor DiamondThis diamond, which originated in India, now belongs to the Britishroyal family. The raja of Malwa owned it for two centuries, until

1304, when it was stolen by the Mongols. In 1739 the Persians tookpossession of it. It witnessed bloody battles until finding its way backto India in 1813, after which point it reached the queen.

Coronationof the QueenMother

The QueenMother's Crown

History

ONLY FOR WOMENBecause this diamond wasbelieved to bring unhappiness tomen, the superstitious QueenVictoria added a clause to herwill stating that the diamondshould only be handed down tothe wives of future kings.

9 LARGE AND 96 SMALL PIECESJoseph Asscher studiedthe huge stone for sixmonths to decide how tocut it; he then divided itinto nine primary stonesand 96 smaller diamonds.

In 1856 this diamond was offered toQueen Victoria as compensation for theSikh wars. She then had it recut. TheKoh-i-noor was diminished to 109 carats.

530 caratsis the weight of the Cullinan I, the largeststone obtained from the original Cullinan find.It is followed by Cullinan II, which weighs317 carats and is set in the imperial crown.

EvalynWalshMcLean

1669 Louis XIV acquires the gem. Hedied in agony of gangrene.

1830 Henry Hope buys the diamondand suffers under the curse; hesoon sells it.

1918 While the stone is in the handsof members of the McLeanfamily, the patriarch and two ofhis daughters die.

ORIGINAL CUT Thepurest of blue from thepresence of boronicimpurities, the diamond'scolor is also influencedby the presence ofnitrogen, which adds apale yellow shade.

FINAL CUT

THE GREAT STAR OF AFRICA This gem is the secondlargest cut diamond in theworld, weighing 530carats. Because it belongsto the British Crown, it ison display in the Towerof London.

13.53

43.3

100

THE TAYLOR-BURTON DIAMONDThis diamond, with a weight of 69.42carats, was auctioned in 1969. The dayafter buying it, Cartier sold it to theactor Richard Burton for $1.1 million. Hiswife Elizabeth Taylor tripledits value when she sold itafter divorcing him.

THE LEGEND OF THE VALLEY OF DIAMONDSAlexander the Great introduced the legend of the Valley of Diamondsto Europe. According to this ancient account, later incorporated intothe book The Thousand and One Nights, there was an inaccessiblevalley located in the mountains of northern India. The bed ofthis valley was covered with diamonds. To obtain them, rawmeat was thrown in the valley and then fetched by trainedbirds, which would return it encrusted with diamonds.

ElizabethTaylor

FINAL CUT

Diamonds are a sign of status, and their monetary value is determinedby the law of supply and demand. First discovered by Hindus in 500BC, diamonds gained fame in the early 20th century when they were

advertised in the United States as the traditional gift from husbands totheir wives. Some diamonds became famous, however, not only for theireconomic value but also for the tales and myths surrounding them.

The Misfortune of Possessing HopeThe Hope Diamond is legendary for the harm it brought to its ownerssince being stolen from the temple of the goddess Sita in India. According

to the legend, its curse took lives and devoured fortunes. In 1949 diamondexpert Harry Winston bought it and in 1958 donated it to the SmithsonianInstitution, in Washington, D.C., where it can be viewed by the public.

LegendOver the years, belief in the curse of the Hope Diamondwas reinforced as its owners fell into ruin. Evalyn WalshMcLean, the last private owner of the diamond, did notsell it even after several tragedies befell her family.

Cullinan, the Greatest FindDiscovered in 1905 in South Africa, this diamond is the biggest everfound. It was sold to the government of Transvaal two years after its

discovery for $300,000 (£150,000). It was then given to Edward VII on theoccasion of his 66th birthday. The king entrusted the cutting of the diamondto Joseph Asscher of The Netherlands, who divided it into 105 pieces.

The Most Common Minerals

36 MINERALS

VIEW FROMABOVE

LATERAL VIEW

KAOLINITE

WATERMOLECULES

SILICATEMOLECULES

SILICATEMOLECULES

COMPACTED

IRON AND MAGNESIUMEXAMPLE: BIOTITEThe color and heaviness of this mineral are causedby the presence of iron and magnesium ions.Known as a ferromagnesian mineral, biotite'sspecific gravity varies between 3.2 and 3.6.

DARK SILICATES

LIGHT SILICATES

Three-dimensionalStructureThree fourths of the Earth's crust is composedof silicates with complex structures. Silicas,feldspars, feldspathoids, scapolites, and zeolitesall have this type of structure. Their maincharacteristic is that their tetrahedrons shareall their oxygen ions, forming a three-dimensional network with the same unitarycomposition. Quartz is part of the silica group.

SimpleStructureAll silicates have the same basiccomponent: a silicon-oxygen tetrahedron.This structure consists of four oxygen ionsthat surround a much smaller silicon ion.Because this tetrahedron does not shareoxygen ions with other tetrahedrons, itkeeps its simple structure.

ComplexStructureThis structure occurs when the tetrahedronsshare three of their four oxygen ions withneighboring tetrahedrons, spreading out to forma wide sheet. Because the strongest bonds areformed between silicon and oxygen, exfoliationruns in the direction of the other bonds, parallelto the sheets. There are several examples of thistype of structure, but the most common onesare micas and clays. The latter can retain waterwithin its sheets, which makes its size vary withhydration.

Silicates, which form 95 percent of the Earth's crust, are the mostabundant type of mineral. Units of their tetrahedral structure, formed bythe bonding of one silicon and four oxygen ions, combine to create

several types of configurations, from isolated simple tetrahedrons to simple anddouble chains to sheets and three-dimensional complex networks. They can belight or dark; the latter have iron and magnesium in their chemical structures.

StructuresThe basic unit of silicates consists of four oxygen ionslocated at the vertices of a tetrahedron, surrounding a

silicon ion. Tetrahedrons can form by sharing oxygen ions,forming simple chains, laminar structures, or complex three-dimensional structures. The structural configuration alsodetermines the type of exfoliation or fracture the silicate willexhibit: mica, which is composed of layers, exfoliates into flatsheets, whereas quartz fractures.

OLIVINE

OXYGEN

SILICON

Quartz has a complexthree-dimensionalstructure composedonly of silicon andoxygen.

THREE-DIMENSIONALSTRUCTURE

Clays are complexminerals with a veryfine grain and asheetlike structure.

CHAINS

UNCOMBINEDSILICATESThis group includes allsilicates composed ofindependenttetrahedrons of siliconand oxygen. Example:olivine.

The quartz crystalmaintains a hexagonal shapewith its six sides convergingto a tip (pyramid).

RESULTING SHAPE

For a quartz crystal toacquire largedimensions, it needs agreat deal of siliconand oxygen, muchtime, and ample space.

A CRYSTAL OFGREAT VOLUME

FE

CA

Calcium is added toits composition.

Iron isadded to its

composition.

MINERAL COMBINATIONS

GRAN ATLAS VISUAL DE LA CIENCIA ROCAS Y MINERALES 37ROCKS AND MINERALS 37

AUGITE MAGNESIUMEXAMPLE: MINERAL TALCThis mineral contains variable amounts ofcalcium, aluminum, sodium, and potassium.Its specific gravity is, on average, 2.7—muchlower than that of ferromagnesian minerals.


The Nonsilicates

are binary compounds. One halite istable salt (or sodium chloride). Haliteshave many uses: fluorite is used in theindustrial production of steel, andsylvite (potassium chloride) is used asfertilizer.

Halides

Carbonates

Hydroxides

Sulfates

Phosphates

Metal associations with oxygen atoms.Ilmenite, hematite, and chromite are oresfrom which titanium, iron, and chromeare extracted. Rubies and sapphires areextracted from corundum.

Oxides

In addition to carbon—which forms minerals suchas diamond and graphite when crystallized—copper, gold, sulfur, silver, and platinum are otherminerals that are found as native elements.

Native ElementsVery Few in a Pure StateIt is rare for native chemical elements to be found in theEarth's crust in a pure state. In general, they must be

extracted from other minerals by means of industrial chemicalprocesses. However, they can occasionally be found in rocks in apure state. Diamonds, for instance, are pure carbon.

In Alloys and CompoundsAs was the case with silicates, it is very difficult to findrocks composed of pure nonsilicate elements—elements

with atoms of only one type. The constituent elements of nature,metal and nonmetal, tend to join together and form compoundsand alloys. From a chemical perspective, even ice, solidified water,is a compound of hydrogen and oxygen atoms. Some compoundsare used as ores, meaning that they are mined for theirconstituent elements. For example, pure aluminum is obtainedfrom bauxite. Other compound minerals, however, are used fortheir specific properties, which can be very different from thoseof each of their constituent elements. This is the case withmagnetite, which is an iron oxide.

MAGNETITE

COPPER

APATITE

MALACHITE

LIMONITE

GYPSUM ROSETTE

PYRITE

0.04 inch (1 mm)

Both apatite, used as fertilizer, andthe semiprecious stone turquoise arephosphates. These materials have acomplex structure based on an ioncomposed of one phosphorus and fouroxygen atoms. These ions, in turn, areassociated with compound ions ofother elements.

Gypsum, widely used inconstruction, is a calcium sulfatethat forms in the sea and containswater in its structure. Withoutwater, calcium sulfate formsanother mineral, anhydrite, which isalso used in construction. Barytineis a sulfate from which the metalbarium is extracted.

are found in metal ores and areassociated with sulfur. Examplesof sulfides are pyrite (iron),chalcopyrite (iron and copper),argentite (silver), cinnabar(mercury), galena (lead), andsphalerite (zinc).

Sulfides

Simpler than silicates, minerals in thisgroup are composed of a complexanion associated with a positive ion.Calcium carbonate (calcite, the maincomponent of limestone) and calciummagnesium carbonate (dolomite) arethe most common carbonates.

Known in chemical terms as a base,these types of minerals appear throughthe association of oxide with water.Limonite, an iron ore used as pigmentbecause of its reddish color, and bauxite(or aluminum hydroxide) are among themost abundant hydroxides. Bauxite isthe ore from which aluminum, a metalthat is becoming more and more widelyused, is extracted.

ASSOCIATION

“FOOL'S GOLD”was an early namefor pyrite becauseof its glitter.

ENCRUSTEDIN ROCKHere crystals areencrusted in slate, ametamorphic rock.

STRUCTUREOF PYRITEThe cubic shape ofcrystals comes fromthe balanced locationof iron and sulfuratoms.

FORMATION OFCHALCOPYRITEIron, copper,and sulfur arepresent.

The greenish colorindicates theformation ofcopper sulfate.

Microscopic formsthat appear whencopper solidifies andcrystallizes

Copper nuggetscan reach a highdegree of purity.

DENDRITES

1.2 inches(3 CM)

FLUORITE

Sulfurs, oxides, sulfates, pure elements, carbonates, hydroxides,and phosphates are less abundant than silicates in the Earth'scrust. They make up eight percent of minerals, but they are very

important economically. They are also important components of rock.Since ancient times, some have been appreciated for their usefulness orsimply for their beauty. Others are still being researched for possibleindustrial uses.

IF STONES COULD SPEAK 52-53

METAMORPHIC PROCESSES 54-55

THE BASIS OF LIFE 56-57

DIVINE AND WORSHIPED 58-59

Formation andTransformation of Rocks

Natural forces create anincredible variety oflandscapes, such as deserts,beaches, elevated peaks,ravines, canyons, and

underground caves. Settings like the onein the picture amaze us and arouse ourinterest in finding out what is hidden inthe cave's depths. Rocks subjected tohigh pressure and temperatures can

undergo remarkable changes. Aninitially igneous rock can becomesedimentary and later metamorphic.There are experts who overcome everytype of obstacle to reach inhospitable

places, even in the bowels of the Earth,in search of strange or preciousmaterials, such as gold and silver. Theyalso look for fossils to learn about life-forms and environments of the past.

ROCKS OF FIRE 42-43

SCULPTED VALLEY 44-45

EVERYTHING CHANGES 46-49

DARK AND DEEP 50-51

SUBTERRANEAN WORLDThis awe-inspiring limestonecave in Neversink Pit(Alabama) looks like no otherplace on Earth.

42 FORMATION AND TRANSFORMATION OF ROCKS

Rocks of Fire


Igneous (from Latin ignis, “fire”) rocks form when magma coming from the rocky mantle (underneaththe crust) rises, cools, and solidifies. When magma comes to the surface as lava and solidifiesrelatively quickly, it creates extrusive rocks, such as basalt or rhyolite. On the other hand, when

magma seeps into caves or between rock layers and slowly solidifies, intrusive igneous rocks, such asgabbro and granite, are formed. These rocks usually have thicker grains and are less dense than theextrusive ones. They are arranged in structures called dikes, sills, and batholiths beneath the surface.Igneous rocks make up most of the Earth's crust.

ASH CONEComposed of pyroclastsof the volcano itself

LACCOLITHis located betweensuperficial layers.

CALDERACollapsed volcanic crater covered with water

A Complex ProcessThe Earth's crust is 44 miles (70 km)deep at most. Farther down, rocks are

molten or semimolten, forming magma thatrises through the crust and opens paths throughcracks, cavities, or volcanoes. Magma cansolidify when it is moving or still or whenunderground or expelled to the surface. Allthese characteristics together with differentmineral compositions create a wide variety ofigneous rocks.

SOLIDROCK

MUD FLATS

LAKE

VOLCANICOUTCROPPING

BRANCHINGLACCOLITH

ERODED LAVA FLOW

BENEATH THE SURFACEPLUTONIC ROCKSMost magma is underground in the form of plutons, which undergo a solidificationprocess. This forms intrusive (or plutonic)rocks. When magma intrudes into verticalfissures, the resulting rock formations arecalled dikes; those between sedimentarylayers are sills; and batholiths are masseshundreds of miles long. In general, intrusiverocks crystallize slowly, and their mineralsform thick grains. But the solidificationprocess will determine the structure; the rock will be different depending on whethersolidification is slow (over millions of years)or fast and whether it loses or gainsmaterials along the way.

ROCKY MANTLE1,800 miles(2,900 km) thick

COREThe outer coreis made of solid

iron and meltednickel.

CRUSTRigid, outermostlayer

LATERAL VENTS

MAIN VENT

PYROCLASTSRock fragmentsand ash thatspread out overmiles

SILLSoccupy the spaces betweenoverlying layers of rocks.

MAGMA CHAMBERreceives magmamaterial from themantle.

MAGMA TEMPERATURE AT ADEPTH OF 125 MILES (200 KM)

2,550º F(1,400º C)

THE TEMPERATURE OFLAVA IN THE CRUST

2,200º F(1,200º C)

GRANITEComposed of feldspar andquartz crystals, it is rich insodium, potassium, and silica.

SILICACONTENT70%

SILICA CONTENTAccording to thetype of lava

50%BASALT ROCKoriginates from highlyliquid fluid magma thatcools quickly.

SURROUNDINGROCK

INTRUSIVEROCK MAGMA RISES

because of the meltedrock's low density.

BATHOLITHcan be an old magmachamber that hassolidified over thousandsof years.

AGATEROCK

MA

GM

A

LAVA

PLATEAUComposed of rhyoliticvolcanic lava (rich in silicon)

DIKEFormed by magma thatintruded into a verticalfracture

Bowen's Reaction SeriesDifferent magma materials solidify at differenttemperatures. Minerals with calcium, iron, and

magnesium crystallize first, giving them a dark coloring(olivine, pyroxene). But sodium, potassium, and aluminumcrystallize at lower temperatures, remaining in the residualmagma until the end of the process. They are present only inpale-colored rock, which crystallizeslater. Sometimes differentstages of the process canbe seen in the same rock.

LAST LAYER TO CRYSTALLIZE

COOLING OFMAGMA

FIRST LAYER TO CRYSTALLIZE

RICH INSODIUM

RICH INCALCIUM

ON THE SURFACEVOLCANIC ROCKVolcanic, or extrusive, rocks are those that reachthe surface as lava because of volcanic activity.They solidify relatively quickly on the surface.Some, like the obsidians, solidify too quickly tocrystallize. This class of rock is distinguished byits viscosity, caused by the low silica content anddissolved gas at the moment of eruption, whichgive these rocks a particular texture. Highly liquidlava, such as basalt, usually covers large surfacesbecause it solidifies on the outside while stillremaining fluid underground.

STOCKSare massiveplutons smallerthan batholiths.DIKES

The structure of the rockdepends on its formationprocess. Thus, a rockresulting from magmaintrusion into a dike willhave a structure andcoloring different from therock around it because ofhaving crystallized faster.

44 FORMATION AND TRANSFORMATION OF ROCKS ROCKS AND MINERALS 45

Yosemite National Park is located 200 miles (320 km) east of SanFrancisco, California. This park is known worldwide for its granitecliffs, waterfalls, crystalline rivers, and forests of giant sequoias. Itcovers an area of 1,190 square miles (3,081 sq km) and extends along

the eastern slopes of the Sierra Nevada range. Yosemite NationalPark has over three million visitors every year.

Sculpted Valley

HALF DOMEGranite monolith ofunique beauty. It is lowerthan El Capitan, being2,160 feet (660 m) high.

87MillionYears Ago

YOSEMITENATIONAL PARKUnited StatesLatitude 37° N

Longitude 119° W

Location

Surface

Visitors in 2005

Opened on

Administered by

California

1,190 square miles (3,081 sq km)

3,380,038

9/25/1890

National Park Service

CASCADESSome rock formations in the park serve as platformsfor waterfalls, especially in April, May, and June whenthe snow melts upstream. The valley has ninewaterfalls, five of which are over 1,000 feet (300 m)high; Yosemite Falls is 2,600 feet (800 m) high. Thisis the highest waterfall in North America and thethird highest in the world.

YosemiteThis park has an averageelevation of 1,300 to 2,000 feet

(400-600 m) above sea level. The geologyof the area is mostly composed of a graniticbatholith, but five percent of the park iscomposed of formations from themetamorphism of volcanic and sedimentaryrocks. Erosion at different elevations and fracturesystems created valleys, canyons, hills, and othercurrent geological formations. The wideseparation between fractures and joints is causedby the amount of silica present in the granite andin the metamorphic rocks.

EL CAPITAN300-foot-high (1,000 m)granite cliff used formountain climbing

FORESTThe park has threegroves of giant sequoias,among other species.

103MillionYears

BRIDAL VEIL FALLSThis huge waterfallformed as a consequenceof glacial thaw in a“hanging” valley.

616 feet(188 m)FREE FALL

CATHEDRAL ROCKSOne of the main rockformations, with compacted and scratched granite walls

103MillionYears Ago

FISSURESThe erosion at rock joints causes fissureswithin them, and this process leads to theformation of valleys and canyons. Thedownward flow of the glacial mass of ice cut and sculpted the valley into a U shape.Today this unique landscape attracts greatnumbers of visitors.

FORMATION OF THE LANDSCAPEErosion in the joints resulted in valleys and canyons. Thestrongest erosive forces of the last several million years havebeen glaciers, which changed the V-shaped valleys created byrivers into U-shaped glacial valleys.

BATHOLITH FORMATION Almost all rocky formations at Yosemite Park are composed of granite; they belong to theoriginal batholith.

1 ASCENTTen million years ago, the SierraNevada underwent a tectonicelevation that caused thebatholith to emerge.

2 EROSION One million years ago, the descending flow of glacial ice gave the valley a U shape.

3

GLACIATION ROCKCompact graniteforming a largebatholith

FISSUREProduced by erosion atrock joints

GRANITE ELEVATION V-SHAPEDSLOPES

U-SHAPEDCANYONS


Everything ChangesEverything Changes


Wind, ice, and water. These natural elements cause great changes in the Earth's landscape.Erosion and transportation are processes that produce and spread rock materials. Then,when these materials settle and become compacted, new rocks are created, which in turn

will revert to sediment. These are sedimentary rocks: the most widely known rocks, they cover 70percent of the Earth's surface. By observing sedimentary rocks of different ages, scientists canestimate how the climate and the environment have changed.

GLACIAL CIRQUEAt the upper end of the valley, the walls erode in asemicircular form.

SLOPESRocks fall from slopes ontoglaciers. They are includedin the material that makesup the moraine.

CANYONTypical result of strongtemperature variationsbetween night and day CENTRAL MORAINE

forms when two valley glaciers meet,creating only one mass of ice.

LATERAL MORAINEFormed by the fragments accumulatedalong the sides of the glacier

FINE SEDIMENTis deposited under theglacier and at its frontend. The depositedmaterial is called till.

TRANSPORTEDROCKwill be deposited on the moraines.

CRACKS

ALLUVIAL CONESediments are deposited at the mouth of canyons.

COLUMNSFormed by the action of the wind and sandabrasion

PEDESTALS Cracks created bythe wind andwatercourses

DEPOSITS Sand accumulatesin low areas.

DESERTPLATEAU

DUNES

OASIS

DESERT TINY GRAINSIn the desert, the windmoves particles in threeways: suspension (very fine grains and dust),transport (the most basic way), and sliding along the surface.

GLACIER FINE AND HETEROGENEOUSGlaciers transport rockfragments, which accumulate inmoraines. They are made up of aheterogeneous material calledtill, which, together with rocks, iscarried along by the glacier.

TRANSPORT OF SEDIMENTS

WIND 3 INCHES(10 CM)

ICESAND

12

EROSIONThe wear and movement of materials on thesurface through the action of water, wind, orice. It can start when rocks are broken down by physical or chemical forces.

TRANSPORTAfter erosion, fragments are transported to an areawhere they will be deposited. In deserts, the windtransports the sand grains, forming dunes; withglaciers, the debris forms frontal and lateral moraines.

TILL

ERRATICSare large rockfragments thatthe glaciertransports anddeposits.

INSELBERGA solitary moundless eroded thanthe flat groundover which it rises

DUNE EROSIONBy transporting sand grainsfrom the crest of the ridge, the wind moves the dunes. The grains can be transportedup to 100 feet (30 m) per year.

TERMINAL MORAINERocks that fall onto the glacier, along with the rock it was already carrying,accumulate at the front ofthe glacier and form what iscalled a terminal moraine.

WINDThe wind andconstant sandabrasion erode the base of a stone peak.

GLACIERMass of ice thatflows down over a landmass.

MUSHROOM FORMATIONSand transported by the wind moldsstratified shapes such as mushrooms.

U-SHAPEDVALLEYSGlaciers erode valleys, forming a U shape becauseerosion is greatest at the bottom.

WIND

DUNES

ACCUMULATEDSEDIMENTS

DesertsThe largest environments sculpted by wind are the deserts. Because of the scarcity of water and the widely varying temperatures, the rock

is broken down by physical forces. Rocks fragment and are swept to low-lyingareas by occasional water currents. Then sand and mud will be swept away by the wind in a process called deflation. Through this process particles can be transported into semiarid regions.

GlaciersThese huge ice masses form on the ground, slowly moving downward through the action of gravity. As they advance, they carry away rocks in

their path. At the head of a glacier valley, the walls erode in a semicircle, formingwhat is called a glacial cirque. The simultaneous, progressive erosion of the wallscreates a pyramidal horn, or peak. The valleys through which a glacier has passedare U-shaped instead of the V shape typical of the erosion of river valleys.

ICE

GLACIER


160 FEET(50 M)

48 FORMATION AND TRANSFORMATION OF ROCKS ROCKS AND MINERALS 49

RAPIDSIn these geographic features,a high volume of matter istransported by river erosion.

SLOPERiver valleys are steep because they are composed of layers of hard rock.

MEANDERS The outside of the curve is where the most sediment isdeposited.

CLIFFA product of lateralundermining

WATERFALLSSofter rock erodes, forming acave with a rocky ceiling thatwill finally crumble and fall.

SEDIMENTATIONWhen the currents that transport sediment lose energy, the sediment is deposited in layers and distributed over extensive areas.

FORMATION OF V-SHAPED VALLEYSUnlike glacial valleys, which areeroded in the shape of a U, river valleys are V-shaped.

RiversClose to their source, rivers flow through areas of high elevation. The water descends there with great force and energy, which

enables the current to transport large boulders. At low elevations, rivers flow more smoothly over sediments, forming meanders and eroding laterally. On reaching the coast, rivers deposit sediments and form estuaries or deltas.

SOLIDROCK

RIVER'S MOUTHInterrupts the shoreline and deliverscontinental sediments.

COASTAL PLAINA plain that usually lies inward from beach

MARINE ABRASIONPLATFORMFlat surface created by a receding cliff

CAVE Caves are cut into therock through abrasion.

CLIFFSoriginate through the erosiveaction of the waves againstthe base of coastal terrain.

CoastsOcean coasts are the most changing landscapes in the Earth'sgeography thanks to a process called coastal drift. The elements

that build up the coastline—wind, rain, and waves—also erode and moldit. Thus, the waves that bring the sediments that form beaches and carrythem away are the same waves that can create or knock down a cliff orcave. Its remnants will be the building material for another beach, alongwith the sediment that comes from rivers and their deltas.

DELTA FORMATIONThe sediment deposited at the river's mouth creates a delta, an area with sandbars through which the river flows invarious directions.

ESTUARYFormer river valley that is nowflooded. It offers the necessaryconditions for depositing muchsediment.

SEDIMENTARYDEPOSITAccumulation ofsediments transported bycoastal (longshore) drift

ALLUVIAL PLAINComposed of sediments

SEDIMENTARYDEPOSITS

BEACH FORMATIONBeaches are formed from the gradual deposits of waves in low-energy coastal zones. They can be made of fine sediment, such as mud and sand, or of largermaterials, such as boulders.

CEMENTATION PROCESSThis is the most important process that transformssediment into rock. Cementation occurs when particlesjoin with the materials precipitated from the watercurrents. Sedimentary rocks are formed through theunion of different minerals that have been dissolved inwater. When the water evaporates or cools, thedissolved minerals can precipitate and form depositsthat accumulate with other sediments, or they can formrocks on their own. Salts and sandstone are commonexamples of cemented rocks.

INITIAL PHASE

FINAL PHASE

RIVERClose to the river'ssource, the current isvery strong, and it erodesand digs into the riverbedto form V-shaped valleys.

RIVERGREAT DISTANCESA river can transportsediments over greatdistances. Rivers originate inelevated areas, from whichthey flow to lower areas andthen to the sea. When thecurrent gathers speed, ittransports big boulders. Whenthe energy is less, the currentcarries only smaller rocks.

COASTLOCAL DEPOSITSAfter each wave breaks, the undertow descends thebeach slope, creating anaccumulation of sand thathas been transported by thewaves in a process called acoastal current. Sand is alsotransported by rivers, whichdeposit sediments in theirdeltas.

WATER

3 FEET (1 M)

WAVES

BOULDER

SAND OR PEBBLES

BEACH

30 FEET(10 M)

COMPACTIONThe successive layers of sedimentary depositscompact the lower ones by exerting pressure on them. This gives rise to diagenesis andlithification, processes that will form new rock.

MINERALDEPOSITS

SEPARATIONBY WEIGHT

TRANSPORT OF SEDIMENTS

WAVES


LAYERSDifferent layersof lithifiedsediments

UNDERWATERSLOPEAlong the coast, the effects oferosion caused by waves are easyto spot. Cliffs are created throughthe erosive action of the waves againstthe base of coastal terrain. As the erosionprogresses, the undermining of the cliff's baseleaves higher rock layers jutting outward, whichthen collapse. The cliff recedes, leaving a flat surfacein the form of a bank called an abrasion platform.

SEDIMENTBANKS

3 4


Acave is a hollow space created essentially through the chemical action of wateron a soluble, usually chalky, material. Caves have three structures: stalactites(conical structures that hang from the cave ceiling), stalagmites (structures

that jut from the cave floor), and columns (created when stalactites and stalagmites join).The cycle of cave formation is called the karst cycle, which lasts a total of around onemillion years. For this reason, young, active caves have noisy streams and cascades,whereas old caves are silent wonders decorated with stalagmites, stalactites, and columns.

Dark and Deep


CANGO CAVES SOUTH AFRICALatitude 33º S

Longitude 18º E

Length

Depth

Location

3.3 miles (5.3 km)

200 feet (60 m)

East of Cape Town

When water dissolves high calcium contentrock through the corrosive effect of carbonic

acid, it forms networks of conduits and galleries.The initial fissures widen not only through thischemical process but also mechanically through the

abrasive action of pebbles and other insolubleelements. Water is filtered until it reaches lowerlevels, leaving in its wake openings arranged inlevels and separated by vertical pits and passagesthat connect the different levels.

The Karst Cycle

Stalactite Formation

Limestone is a rock composedalmost exclusively of calcium

carbonate, which dissolves in naturally acidwater. Rainwater absorbs carbon dioxide from theair and microorganisms from the ground, becoming a weak acid. When filtered, it can dissolve limestoneover time. If this water drips into a cave, it loses carbondioxide to the air and deposits the excess calcium instalactites and stalagmites, thereby maintaining chemicalequilibrium. Stalactites are excellent examples of chemicalsedimentary rocks.

COLUMNIf stalactites

and stalagmitesgrow until they

join together, they become

columns.

130 feet(39 m)

THE HIGHEST COLUMN IN THE WORLD

65º F(18º C)

IDEAL TEMPERATURE FORTHE PRECIPITATION OFCARBONATE

100 feet(30 m)THE TALLEST STALAGMITEIN THE WORLD

23 feet (7 m)THE BIGGEST STALACTITEIN THE WORLD

STRUCTURE OF THESTRATUM OF A CAVEThe ground's originalstructure is composed ofpermeable limestone. Ithas fissures throughwhich river or rainwateris filtered. This starts theerosive process.

1

INITIAL CAVEWater, following the contour of the terrain, forms an underground river.The first calcite or calciumcarbonate deposits start to form in the shape ofstalactites.

2

EXTENDED CAVESYSTEMFormed when severaltunnels are joinedtogether. Sometimes thesurface of the soil startsto sink, creatingsinkholes. If the caveextends below the watertable, tunnels are formed.

3

FLAT GROUND

TUNNEL

DRY GALLERY

TUNNEL

VAULT

CALCITEDEPOSITS

WATERFILTRATION

UNDERGROUNDSEQUENCE

PERMEABLELIMESTONE

CAVERN

FISSURE

IMPERMEABLE ROCK

SINKHOLE

CANGO CAVESIsolated in a narrow strip of limestone from thePrecambrian, in the highlands of Oudtshoorn, the CangoCaves are remarkable for their abundant deposits ofcalcite. They are left over from a larger channel belowthe water table. This channel dried up when theneighboring surface valleys were worn down to lowerlevels. The impressive stalagmites were then formed..

STALACTITEScan form on ceilings and cementfloors, although they form muchfaster in a cave's naturalenvironment that contains carbon-rich solutions.

MORE LAYERSEach successive droplet that falls deposits anotherfine calcite layer.

3

INTERIOR TUBEThe layers form around a narrow pipe (0.02 inch [0.5mm]) through which the water seeps.

4

STALACTITEIf many droplets aredeposited over this pipe,stalactites are formed.

5

WATER DROPLETEvery stalactite starts froma simple water dropletcontaining dissolved salts.

1

CALCITEWhen the droplet falls, itleaves behind a narrowcalcite trail.

2

WaterDroplet

Other FormationsA passing underground current forms two types of landscape: canyons and tunnels. Underground

rivers and waterfalls above the water table create deep, undulating canyons by eroding and dissolving limestone and by abrading the rock layers with sediment. Below the water table, caves are full of water that movesslowly, dissolving walls, floors, and ceilings of carbonate rock to create tunnels.

STALAGMITEWater droplets containingdissolved carbonatecreate stalagmites as theydrip down.


If Stones Could Speak R

ock strata form from sediments depositedover time in successive layers. Sometimesthese sediments bury remains of organisms

that can later become fossils, which provide keydata about the environment and prehistoric life onEarth. The geologic age of rocks and theprocesses they have undergone can bediscovered through different methodsthat combine analyses ofsuccessive layers and thefossils they contain.

Fossils succeeded one another in adefinite order, which makes itpossible to date past events. Theexistence of identical fossils ondifferent continents helps establishcorrelations and assigns the same ageto widely separated geographic areas.

PRINCIPLE OF SUCCESSION

Rock Layers and the Passage of Time

Rock layers are essential for time measurementbecause they retain information not only about the

geologic past but also about past life-forms, climate, andmore. The principle of original horizontality establishesthat the layers of sediment are deposited horizontallyand parallel to the surface and that they are definedby two planes that show lateral continuity. If layersare folded or bent, they must have been alteredby some geologic process. These ruptures arecalled unconformities. If the continuitybetween layers is interrupted, it meansthat there was an interval of time and,consequently, erosion in the layerbelow. This also is calledunconformity, since it interruptsthe horizontalityprinciple.

A Fossil's AgeFossils are remains of organisms that lived in the past. Today scientists use several procedures, including carbon-14 dating, to estimate their age.

This method makes it possible to date organic remains with precision from as long ago as 60,000 years. If organisms are older, there are other methods forabsolute dating. However, within a known area, a fossil's location in a givensedimentary layer enables scientists to place it on an efficient, relative time scale.Following principles of original horizontality and of succession, it is possible to find out when an organism lived.

When it dies, an animal canbe submerged on a riverbed,protected from oxygen. Thebody begins to decompose.

1.The skeleton is completelycovered with sediments. Over the years, new layers areadded, burying the earlier layers.

During fossilization, moleculesof the original tissue arereplaced precisely withminerals that petrify it.

2.

Once the water disappears, thefossil is already formed andcrystallized. The crust'smovements raise the layers,bringing the fossil to the surface.

3.


TRILOBITESare extinct arthropods. Theywere solitary marine creatures,and they had a segmentedbody and an exoskeleton ofthe protein chitin, with pairsof jointed limbs. Togetherwith graptolites they areone of the mostcharacteristic fossilsfrom Paleozoic marinesediments.

Unconformity

AngularUnconformity

Colorado River

Disconformity

Paraconformity

COCONINOPLATFORM

TONTOPLATFORM

TONTOPLATFORM

ZoroasterGranite

VISHNU SCHISTS

MuavLimestone

PRECAMBRIAN

CAMBRIAN

DEVONIAN

CARBONIFEROUS

PERMIAN

Unconformity between the Tonto Group and theRedwall Limestone indicatesa temporal hiatus. Betweenthe Redwall Limestone andthe Supai Group, there istemporal continuity.

TEMPORAL HIATUS

Period

HermitShale

460 feet (140 m)

1,000 feet (310 m)

UNKAR GROUP

REDWALL LIMESTONE

TONTO GROUP

SUPAI GROUP

Erosion exposes the fossilto full view. With carbon-14dating, scientists candetermine if it is less than60,000 years old.

4.

CononinoSandstone

The Grand Canyon tells the historyof the Earth in colorful layers on itswalls. The Colorado River has beencarving its way through the plateaufor six million years. The layersalong the river provide an

uninterrupted account of geological history.

CONTINUITY

Bright AngelShale

GONDWANA

PALEOSIBERIA

EUROAMERICA

GRAND CANYONColorado RiverArizonaLatitude 36° N

Length 112° W

ROCKS AND MINERALS 5554 FORMATION AND TRANSFORMATION OF ROCKS

As the pressure increases on the rocks,the mineralogicalstructure of rocks isreorganized, whichreduces their size.

PRESSURE

Intermediate Crust

1

2

SlateIn environments

with high temperatureand pressure, slates willbecome phyllites.

SchistLower Crust

The closer the rock is tothe heat source and thegreater the temperature,the higher the degree ofmetamorphism thattakes place.

TEMPERATURE

1

2

Magma

Sandstone

Magma

Schist

Limestone

Quarzite

Hornfels

MarbleScotland was raised in the Caledonianorogeny 400 million years ago. This pressureproduced the gneiss shown in the photo.

SCOTLAND, United KingdomLatitude 57° NLongitude 04° W

Regional MetamorphismAs mountains form, a large amount of rock is deformedand transformed. Rocks buried close to the surface

descend to greater depths and are modified by highertemperatures and pressures. This metamorphism coversthousands of square miles and is classified according to thetemperature and pressure reached. Slate is an example of rock affected by this type of process.

Contact MetamorphismMagmatic rocks transmit heat, so a body of magma can heat rocks on contact. The affected area, located

around an igneous intrusion or lava flow, is called an aureole.Its size depends on the intrusion and on the magma'stemperature. The minerals of the surrounding rock turn into other minerals, and the rock metamorphoses.

Dynamic MetamorphismThe least common type of metamorphism,dynamic metamorphism happens whenthe large-scale movement of the crustalong fault systems causes the rocks tobe compressed. Great rock masses thrustover others. Where they come in contactnew metamorphic rocks, calledcataclasites and mylonites, are formed.

Metamorphic ProcessesW

hen rocks are subjected to certain conditions (highpressure and temperature or exposure to fluids withdissolved chemicals), they can undergo remarkable

changes in both their mineral composition and their structure.This very slow process, called metamorphism, is a veritabletransformation of the rock. This phenomenon originatesinside the Earth's crust as well as on the surface. Thetype of metamorphism depends on the nature of theenergy that triggers the change. This energy can beheat or pressure.

FUSIONAt this temperature, most rocks start to melt until they become liquid.

1,470° F(800° C)

SCHISTVery flaky rock produced bymetamorphism at intermediatetemperatures and depths greater than six miles (10 km). The mineralsrecrystallize.

930° F(500° C)SLATE

Metamorphic rock of low gradethat forms through pressure at about 390° F (200° C). It becomes more compact and dense.

570° F(300° C)

GNEISSProduced through highly metamorphicprocesses more than 12 miles (20 km)beneath the surface, it involves

extremely powerful tectonic forcesand temperatures near the

melting point of rock.

1,200° F(650° C)


Much of the Earth's crust is covered with a layer ofsediment and decomposing organic matter. This layer,called soil, covers everything except very steep slopes.Although it is created from decomposing plant andanimal remains, the soil is a living and changingsystem. Its tiniest cavities, home to thousands ofbacteria, algae, and fungi, are filled with water or air.These microorganisms speed up the decompositionprocess, turning the soil into a habitat favorable toplant roots as well as small animals and insects.

HOW IT FORMS

Years passed since glaciation.

0

3 ft(1 m)

7 ft(2 m)

10 ft(3 m)

20%of the

world's landsurface

14%of the

world's landsurface

10%of the

world's landsurface

0.2%of the world'sland surface

300 years

PERMAFROSTAreas near the polesThe soil is saturatedwith frozen water. Inthe parts that thaw, big puddles are formed. Because of itscharacteristics, many animals cannot live there.

1 2 3 4 5

The Basis of Life Living Organisms in the SoilMany bacteria and fungi live in the soil; their biomass usually surpasses that ofall animals living on the surface. Algae (mainly diatoms) also live closest to the

surface, where there is most light. Mites, springtails, cochineal insects,insect larvae, earthworms, and others are also found there.Earthworms build tunnels that make the growth of rootseasier. Their droppings retain water and containimportant nutrients.

Different CharacteristicsObserving the soil profile makes it possible to distinguish layers called horizons. Each layer has

different characteristics and properties, hence theimportance of identifying the layers to studyand describe them. The surface layer is rich inorganic matter. Beneath is the subsoil,where nutrients accumulate and someroots penetrate. Deeper down is alayer of rocks and pebbles.

Rock CycleSome rocks go through the rock cycle to form soil. Under the action of erosive agents, rocks from the Earth's crust take on

characteristic shapes. These shapes are a consequence partly of the rock's own composition and partly of several effects caused by erosiveagents (meteorological and biological) responsible for breaking down rocky material.

0 50 100 150 200 250 300

EARTHWORMSIt takes approximately6,000 earthworms toproduce 3,000 pounds(1,350 kg) of humus.

BEDROCKThe continuous breakdownand erosion of the bedrockhelps increase the thickness of the soil. Soil texture alsodepends to a great extent onthe type of bedrock on whichit forms.


Types of SoilIn the soil we find bedrock materials that have beengreatly altered by air and water, living organisms, and

decomposed organic materials. The many physical andchemical transformations that it undergoes produce differenttypes of soil, some richer in humus, other with more clay, andso on. The soil's basic texture depends to a great extent onthe type of bedrock from which the soil is formed.

Organisms are born, live, reproduce, and die on a natural layer of soil.From this layer, crops are harvested, livestock are raised, andconstruction materials are obtained. It establishes the link between

life and the mineral part of the planet. Through the action of climate andbiological agents, soil forms where rocks are broken down.

The time needed for the naturalformation of soil with its three basic layers, or horizons.

Clouds of dust and ash are released to the atmosphere. Ash andotherpyroclasticmaterialsaredepositedin layers.

These layerscompressand harden.

Igneous rock coolsdown anderodes.

A volcanoexpels lava andpyroclasticmaterial.

Some sedimentaryand metamorphicrocks erode,forming new strata.

Heat and pressure canrecrystallize the rockwithout melting it,turning it into anothertype of rock.

Igneous and plutonicrocks form asmagma cools andsolidifies below theEarth's surface.

Magma rises to thesurface and comesout as lava throughthe volcano.

If it is hot enough, the rock can turn into magma again.

The rock melts toform magma.

IGNEOUS ROCKExtrusive rocks form as the lavacools.

METAMORPHIC ROCK

SEDIMENTARY ROCK

IGNEOUS ROCK

EROSION

UPPER LAYERThis layer is dark and rich innutrients. It contains anetwork of plant roots alongwith humus, which is formedfrom plant and animalresidues.

The glacierdragssediments.

The barerock andgravelremain.

Moss anddwarfshrubsgrow.

Small trees manage totake root.

Animals and plants thatdie help to enrich thesoil.

RANKERdevelops on top of slightly alteredbedrock. It is typical in high mountains,especially if it forms on granite or otheracidic rocks.

SUBSOILcontains many mineral particlesfrom the bedrock. It is formedby complex humus.

DESERTICArid soilContaining very little humus, itrests directly on mineral depositsand rock fragments.

LATERITETypical tropical soilWith abundant rains and humidity in these zones, the soil iswell drained. The rain leaves a mix of oxides and hydroxidesof aluminum, iron, manganese, nickel, and other minerals inthe soil. This represents 70 percent of the world's ironreserves.

HUMUSis the substance composed oforganic materials, usually foundin the upper layers of soil. It isproduced by microorganisms,mainly acting on fallen branchesand animal droppings. The darkcolor of this highly fertile layercomes from its high carboncontent.

Uluru contains some of the most representative features of the ancestral history of the Aborigines. The caves surrounding the base of the rock have some Aboriginal paintings illustrating the paths andlimits of the Dream Time. Many carvings in the caves are considered to be of divine origin.

CAVE PAINTINGS

Externsteine Made of oddly twisted limestone rocks,Externsteine is located in the Teutoburg

Forest north of the Rhine River in Rhineland,Germany. It was the place of heroic myths andGerman legends. It is also related to theScandinavian Eddas and, during Nazism, to theAryan myth. According to popular belief, thestones were placed there at night by giants; theywere then burned by the devil, which explainstheir grotesque appearance.

UluruSacred place for Australian Aborigines for thousands of years,Uluru (Ayers Rock) is four miles (9.5 km) in circumference and

rises 1,100 feet (340 m) above the Australian desert. Uluru wasdiscovered by Caucasians in 1872 and renamed Ayers Rock in honorof the Australian Prime Minister Henry Ayers. In this enormoussandstone mass, dozens of dream paths traversed by the Aboriginesand the paths already traveled by their ancestors in the pastconverge through a series of myths. In this manner, all the sacredplaces are connected. On the rock are forms such as Kuniya womenand the wounded head of the Liru warrior, among others.

The Black Stone of the Ka`bah

Located in one corner of the Ka`bah, the Black Stoneis the most sacred treasure of the Islamic world. The

Ka’bah is a cubic building located in Mecca, toward whichMuslims face as they pray five times a day. The stone'sexposed surface is 6 x 8 inches (16 x 20 cm), and its piecesare held together by a frame with a silver band. Muslimsrelate its origin to Adam and say that Abraham and his sonIshmael built the Ka`bah, but it was the Prophet Muhammadwho converted Mecca into the sacred center of Islam in the7th century.

ROCKS AND MINERALS 5958 FORMATION AND TRANSFORMATION OF ROCKS

Divine and WorshipedF

ormed millions of years ago, some rocks enjoy the privilege of being considereddeities. Pagans, Christians, Muslims, and Aborigines of Australia base part of theirbeliefs on the myths, properties, or legends of a rock. Among the best known are

Uluru (Ayers Rock), the Black Stone located in the cube-shaped sepulcher of the Ka`bah,and the rocks of Externsteine, a destination of Christian pilgrimages and a sacred sitefor many ancient pagan religions. Their origins are described and studied in theology aswell as in geology. Resistant to the passing of time, they are transformed into mythsthat remain to the present.

100 feet(30 m) the height of the Externsteineformation. It consists of fivelimestone pillars, riddled with caves,passages, and secret chambers.

ULURU-KATA TJUTANATIONAL PARK,Australia

Latitude 25° SLongitude 131° E

The great reddish rock of Uluru was created during the Alice Springs orogeny,400 million years ago. The sandstone andconglomerates that formed the ancientalluvial fans folded and fractureddeeply, turning horizontal layers on their ends.

Each crack, protuberance, or groove of a rock has meaning toAborigines. For example, a rock'sorifices symbolize the eyes of a dead enemy.

Beliefs

Muslims who have the necessarymeans are expected to go toMecca at least once in their lives.

MUSLIM TRADITION

ORGANIC ROCKS 70-71

COMMON METAMORPHIC ROCKS 72-73

INCREDIBLE PETRA 74-75

Classes of Rocks

Different types of rocks can bedistinguished based on theirluster, density, and hardness,among other properties. Ageode looks like a common

rock on the outside, but when it is cut inhalf, a fantastic range of colors andshapes can be revealed. The severalclasses of rocks can also be groupedaccording to how they formed, giving us

the categories of igneous, metamorphic,and sedimentary rocks. Mostcharacteristics of rocks depend on theirconstituent minerals. There are alsoorganic rocks, formed through the

accumulation of the remains oforganisms that decomposed millions ofyears ago. Coal and some types ofcarbonate and siliceous rocks are part ofthis group.

HOW TO IDENTIFY ROCKS 62-63

IGNEOUS ROCKS 64-65

MARINE SEDIMENTS 66-67

COLLECTION OF DETRITAL ROCKS 68-69

BEAUTIFUL AND STRANGEThe inside of a geode, a rockfilled with crystals, usuallydisplays a beautiful formation.

RROCKS AND MINERALS 6362 CLASSES OF ROCKS

How to Identify RocksR

ocks can be classified as igneous, metamorphic, or sedimentaryaccording to the manner in which they were formed. Their specificcharacteristics depend on the minerals that constitute them. Based on

this information, it is possible to know how rocks gained their color, texture,and crystalline structure. With a little experience and knowledge, people canlearn to recognize and identify some of the rocks that they often see.

ShapesThe final shape that a rock acquiresdepends to a great extent on its

resistance to outside forces. The coolingprocess and subsequent erosion alsoinfluence the formation of rocks. Despitethe changes caused by these processes, itis possible to infer information about arock's history from its shape.

Mineral CompositionRocks are natural combinations of two or more minerals.The properties of rocks will change in accordance with

their mineralogical composition. For instance, granite containsquartz, feldspar, and mica; the absence of any of theseelements would result in a different rock.

ROUNDEDThe wear caused byerosion and transportgives rocks a smoothshape.

ANGULARRocks have this shapewhen they have not beenworn down.

WHITEMARBLE

IMPURITY

WHITEMARBLE

PEGMATITE

WHITEMARBLE

FractureWhen a rock breaks, its surface displaysfractures. If the fracture results in a flat

surface breaking off, it is called exfoliation.Rocks usually break in locations where theirmineral structure changes.

Texturerefers to the size and arrangement of grains thatform a rock. The grains can be thick, fine, or even

imperceptible. There are also rocks, such as conglomerates,whose grains are formed by the fragments of other rocks.If the fragments are rounded, there is less compaction, andthe rock is therefore more porous. In the case ofsedimentary rocks in which the sedimentary cementprevails, the grain is finer.

ColorThe color of a rock is determined by the color ofthe minerals that compose it. Some colors are

generated by the purity of the rock, whereas others areproduced by the impurities present in it. Marble, forinstance, can have different shades if it containsimpurities.

GRAINis the size of theindividual parts of arock, be theycrystals and/orfragments of otherrocks. A rock's graincan be thick or fine.

WHITEIf the rock is a marblecomposed of pure calcite ordolomite, it is usually white.

BLACKVarious impurities giverise to different shadesin the marble.

CRYSTALS

form when a melted rock coolsand its chemical elementsorganize themselves. Mineralsthen take the shape of crystals.

0.4 inch(1 cm)

0.4 inch(1 cm)

AgeBeing able to accurately determinethe age of a rock is very useful inthe study of geology.

64 CLASSES OF ROCKS

Formed from magma or lava, igneous rocks can be classified according to theircomposition. This classification specially takes into account: the relative proportion ofsilica, magnesium, and iron minerals found in these type of rocks; their grain size

(which reveals how fast they cooled); and their color. Rocks that contain silica, along withmuch quartz and feldspar, tend to have pale colors; those with low silica content have darkcolors created by iron and magnesium-containing minerals, such as olivine, pyroxene, andamphiboles. A rock's texture is determined by the configuration of its crystal grains.

Igneous Rocks


Underground: Plutonic or Intrusive RocksRocks of this type formed through the solidification of magma masses deepwithin other rocks. In general, they have undergone a slow cooling process in

the Earth's crust, which has permitted the formation of pure mineral crystals largeenough to be seen with the unaided eye. Usually they display a compact structureand have low porosity. Depending on the composition of the magma, there are acidicplutonic rocks (rich in silicon) or basic rocks (with low silicon content). Granite isthe most common type of intrusive rock.

Extrusive Rocks, Products of VolcanoesExtrusive rocks form through the fast cooling of magma on or near theEarth's surface. Their structure and composition are closely related to the

volcanic activity in the areas where they emerge. Because they are typicallyproducts of a fast solidification process, they usually have a very fine grain. Whenthey are expelled from a volcano, they do not have a chance to crystallize beforethey cool, so they acquire a vitreous (glasslike) texture.

THE MINIMUM DEPTH ATWHICH GRANITE FORMS

1 mile(1.6 km)

THE MOST COMMONSHAPE INTO WHICHBASALT CRYSTALLIZES

Hexagon

PEGMATITE IS ASSOCIATEDWITH THE PRESENCE OFGEMS AND RARE METALS.

Index

GRANITEThis rock is formed by big grains offeldspar, quartz, and mica. Its light-colored components indicate anabundance of silicon and that therock is acidic. Because of its greatresistance to wear, granite is oftenused as a construction material.

PERIDOTITEThis rock is mainly composed ofolivine (which gives it a greenishcolor) and pyroxene. It is lessthan 45 percent silicon and isrich in magnesium, a very lightmetal. It is abundant in theupper layers of the mantle (at adepth of about 40 miles [60km]) as a residue of old crust.

GABBROThis rock contains ferromagnesianminerals, such as olivine, pyroxene, andaugite, which form dark-coloredcrystallizations, and feldspars, which give awhite coloring to some of its parts. Gabbrogenerally solidifies slowly, leaving it withthick grains.

PEGMATITEThis very abundant, acidicrock has a mineralcomposition identical to thatof granite. However, itssolidification process wasvery slow, thus enabling itscrystals to grow to a size ofseveral feet.

PUMICEThis rock is produced from lava with ahigh silicon and gas content, whichgives it a foamy texture. This explainsits porous consistency—acquiredduring rapid solidification—whichenables it to float in water.

BASALTThis rock forms most of the oceaniccrust. Its low silicon content gives itits characteristic dark color (betweenblue and black). Its rapid cooling andsolidification gives it a very fine grain.Because of its hardness, it is used tobuild roads; it is not, however, used tomake paving stones becauseit is too slippery.

OBSIDIANThis rock is black; its shades vary inaccordance with its impurities. Because itundergoes rapid cooling, its structure isvitreous, not crystalline; thus, it iscommonly called volcanic glass. Strictlyspeaking, obsidian is a mineraloid. It wasoften used to make arrowheads.

GRANODIORITEThis rock is often confused with granite, but itis grayer since it contains larger numbers ofquartz and sodic plagioclase crystals than itdoes feldspar. It has thick grains and containsdark crystals called nodules.

MACROPHOTOGRAPHYOF PINK GRANITE

PEGMATITE ISNATURALLY SMOOTH.

CRYSTAL JOINED BYVITREOUS MASS

MACROPHOTOGRAPHYOF GRANODIORITE

GEOMETRIC PRISMSThese prisms were formed inthe Giant's Causeway(Northern Ireland) throughcontraction, expansion, andrupture of basaltic lava flowsthat crystallized gradually.

Dikes and Sills: Rocks Formed in SeamsSome types of igneous rocks are formed from ascending magma thatsolidifies in seams or fissures. The resulting sheetlike body of rock is called a

dike if it has a vertical orientation or a sill if it has a horizontal orientation. Thecomposition of these rocks is similar to those of intrusive and extrusive rocks. Infact, like dikes and sills, intrusive and extrusive rocks can also form in cracks.However, the manner in which the materials in a sill or dike solidify causes them toform crystalline structures different from those of their volcanic and plutonicrelatives. PORPHYRITICS

These rocks solidify intwo phases. In the first,slower phase, thickphenocrystals form.Then in the secondphase, the phenocrystalsare dragged along bymagma, which causesthe formation of smaller,vitreous crystals. Thename porphyritic alludesto the color purple.

Old Reefs

PaleozoicCoastalArea

CurrentStateBoundary

CurrentCoastalBoundary

66 CLASSES OF ROCKS ROCKS AND MINERALS 67

Coral Reefsare rocky structures resistant to the action of waves andto the movement of the water. They are formed and/or

colonized by photosynthetic organisms and marine animals,some of which have calcareous skeletons, as in the case ofcoral polyps. These soft organisms, related to anemones andjellyfish, live in colonies. When their solid calcareous skeletonssediment, they turn into calcite. They live in symbiosis withsingle-celled algae known as zooxanthellae.

FLAT CORALCorals typically growin colonies and createreefs, layer by layer.

HOW CORAL GROWS

LAYERS OFMOTHER-OF-PEARLCombination ofcalcite and a proteincalled conchiolin

1

COQUINA CALCITE

PEARL LUSTERresults from theoptical properties ofcrystallized mother-of-pearl.

2

Grain ofSand

BARRIER REEFPARALLEL TOTHE COAST

REEFLAGOON

CONTINENTALSHELF

Natural Pearl

Pearl (interior)

Oyster

EnvelopingMotion

68° F(20° C)MINIMUM WATER

TEMPERATURE NEEDED

FOR THE FORMATION OF

CORAL REEFS

THE HEIGHT THAT A REEF CAN GROWTOWARD THE SURFACE IN ONE YEAR

3 feet (1 m)

Pearl, Jewel of the SeaIn order to protect themselves from the intrusionof a foreign body—such as a sand grain that

becomes lodged between their mantle and shell—bivalvemollusks cover the intruding object with alternatingconcentric layers of protein (conchiolin) and calcite. Thisprocess ultimately yields a pearl. Fine pearls are producedby pearl oysters (Pinctada) in the warm, clear waters oftropical seas.

FROM SEDIMENT TO ROCKUnder pressure from overlying layers,sediments are compacted and lithified,reducing their volume by 40 percent.Other substances dissolved in water(calcite, silica, and iron oxide) fill up theinterstices between the particles ofsediments, and when the waterevaporates, cementation occurs.

CORALS IN ARIZONAIn the first phase of the Paleozoic Era(500 million years ago), the currentmountainous region of the AmericanWest was a coastal area with much coralactivity. This is how the abundantcalcareous formations that canbe seen today in Arizona'sGrand Canyon originated.These formations alsocoexist with muchyounger rocks.

CalcareousSkeleton

LivingPolyp

BranchedPolyp

BRAIN CORALBRANCH CORAL

Layers ofMother-of-Pearl

Marine SedimentsS

edimentary rocks can also form through the accumulation and lithificationof organic remains. The most common example is coral reefs, which developunderwater, surrounding the coasts of many temperate seas. Many

limestone rocks also originate this way; they are made of calcium carbonate(calcite) or calcium and magnesium (dolomite). Because of their porousconsistency, they often serve as repositories for fossil fuels, which are also oforganic origin. Other rocks, like coquina, form through the accumulation offragments of marine shells, lithified over time as materials filled and cementedtheir interstices.

Collection of Detrital Rocks


Among the sedimentary rocks, detrital rocks are the most abundant. They formthrough the agglomeration of rounded fragments (clasts) of older rocks. Dependingon the size of the clasts, they are classified as (from smallest to largest) pelite,

lutite and limestone, sandstone, and conglomerates. The analysis of their components,cementation matrix, and arrangement in layers makes it possible to reconstruct thegeologic history both of the rocks and of the areas in which they are found.Some break off easily and are used in industrial processes andconstruction as rock granules, whereas others areappreciated for their toughness and hardness.

ConglomeratesMost of the grains that compose these rocks are larger than 0.08inch (2 mm). In some cases, it is possible to identify with the

unaided eye the primary rocks from which a conglomerate is formed. Asa result, it is possible to determine the areas where the sedimentsoriginated. Accumulations of gravel and cementation material canindicate either slopes in the rocks where the conglomerates formed orthe action of fluvial currents. All this information makes it possible toreconstruct the geologic history of a rock.

Clay, Lime, and AshThese materials form the less porous, fine-grained detritic rocks. Lutites arerocks of clay, composed of particles whose diameter does not exceed

0.0002 inch (0.004 mm). In general, they are compacted and cemented throughchemical precipitation. Limestone rocks are also called limolites, named after lime,a sedimentary material with a somewhat thicker grain (up to 0.0025 inch [0.06mm]). Some rocks composed of volcanic ash have a similar granulation. Theserocks are very important in construction.

GRAYWACKEhas a defined proportion of calciumcarbonate, quartz, feldspar, and mica. Itdiffers from common sandstone because itcontains a higher amount of cementationmaterials (more than 15 percent), whichform its grain matrix. This makes it morecompacted.

CHALKComposed of calcite debris ofbiochemical origin, thismineral originates in the seanear the coast. After beingeroded and transported, itaccumulates on slopes whereit becomes compacted. Thechalk we use on blackboardsis, in reality, gypsum.

COMPACTED ASHIt is possible to find one or morelayers of fine-grained pyroclasticmaterial (volcanic ash) in manysedimentary rocks. Rocks formedfrom larger pyroclasts, whichsolidified in the air during aneruption before they touched theground, are rarer. Their origin isigneous, but their formation issedimentary. TUFF

is rock that is formed from deposits ofvolcanic ash that has been cemented together.There are several types: crystalline tuff, whichis largely composed of igneous glass; lithictuff, which contains rock fragments; andhybrid tuff, which is formed from fragmentedvolcanic material combined with some clay.

CLAY(KAOLINITE)When hydrated, it increases in size.

MICROPHOTOGRAPHOF BRECCIA

40%THE REDUCTION IN THE VOLUMEOF CLAY AS IT IS COMPACTED

CONGLOMERATEFormed by large fragments, they aregood examples of sediments that have beencompacted after landslides. The irregularityof this specimen's clasts points to a chaoticorigin, which could be alluvial in nature orassociated with a glacial moraine.

BRECCIAIts grains are thick but with straight anglesand edges. This shows that the sedimentshave not traveled far and that cementationhas taken place near the area from whichthe materials originated.

A Variety of SandstonesSandstone is rock composed of grains that are mostly between 0.003 and0.08 inch (0.06 and 2 mm) in size. Sandstones are classified according to

their mineral composition, their level of complexity (or geologic history), and theproportion of cementation material they contain. Quartzarenite (which is morethan 95 percent quartz), arkose (which is mostly feldspar), red sandstone (whichis cemented by iron compounds), and graywacke belong to this class of rocks.

SANDSTONEis made up of small grains ofsand that are here stratifiedby color and texture. Thistype of sandstone indicatesthat an alternatingprocess of sedimentationinvolving two types ofparticles has occurred.

68 CLASSES OF ROCKS

CLAYThe substance commonlyknown as clay is anunconsolidated rock, madeof hydrated aluminumsilicates and typically full ofimpurities. Kaolin is thename for pure granularclay; it is soft and whiteand keeps its color evenafter it has been fired in akiln. It has scale-shapedmicrocrystals and generallycontains impurities.

ARKOSEpossesses a varied composition,although it contains up to 25percent quartz and feldspar.Generally, it has a porousconsistency, and less than onepercent of its interstices areempty. In this specimen, thepinkish section is composed offeldspar, and the white portionis quartz.

COMPACTEDVery fine sediment

20%OF SEDIMENTARYROCKS ARESANDSTONES.

85%PERCENTAGE OFCLASTS LARGER THAN0.08 INCH (2 MM)

Organic Rocks


Organic rocks are composed of the remains ofliving organisms that have undergoneprocesses of decomposition and compaction

millions of years ago. In these processes, thegreater the depth and heat, the greater thecaloric power and thermal transformation ofthe rock. The change experienced by thesesubstances is called carbonization.

OF THE PRIMARY ENERGYCONSUMED IN THE WORLD

COMES FROM COAL.

26%

Transformation ofVegetation into Hard Coal

VegetationOrganic compounds on the surfacebecame covered by oxygen-poor waterfound in a peat bog, which effectivelyshielded them from oxidation.

1.

PeatThrough partial putrefaction andcarbonization in the acidic water of thepeat bog, the organic matter changesinto coal.

2.

Ligniteis formed from the compression of peat thatis converted into a brown and flakysubstance. Some primary plant structurescan still be recognized in it.

3.

Coalhas a content of less than 40 percentmineral substance on the basis of drymaterial. It has a matte luster, is similar tocharcoal, and is dirty to the touch.

4.

Anthraciteis the type of coal with the greatest concentrationof carbon. Its high heat value is mostly due to thistype of coal's high carbon content and lowconcentration of volatile material. It is harder anddenser than ordinary coal.

5.

Coal FormationPlant materials, such as leaves, woods, barks, andspores, accumulated in marine or continental basins

285 million years ago. Submerged in water and protectedfrom oxygen in the air, this material slowly became enrichedwith carbon through the action of anaerobic bacteria.

Contains 95% carbon

Contains 80% carbon

Contains 70% carbon

Contains 60% carbon

Vegetationthat willform peatafter dying

Peat iscompactedandtransformed.

Coal richin humicacids

Coal:gas andfuel isobtained

Metamorphismwhere gasesand oils arereleased

SURROUNDINGTEMPERATURE

ExertedPressure.

LEGEND

up to 1,000 feet(300 m)

DEPTH

up to 77º F (25º C)

TEMPERATURE

1,000 to 5,000 feet (300 to 1,500 m)

DEPTH

up to 104° F(40° C)

TEMPERATURE

5,000 to 20,000 feet (1,500 to 6,000 m)

DEPTH

up to 347° F(175° C)

TEMPERATURE

20,000 to25,000 feet(6,000 to 7,600 m)

DEPTH

up to 572° F(300° C)

TEMPERATURE

WORLD COAL RESERVESBillions of tons

AsiaPacific296.9

MiddleEast0.4

Europe andEurasia

287.1

NorthAmerica254.4

Africa50.3

Central andSouth America19.9

WORLD PETROLEUM RESERVESBillions of barrels

AsiaPacific

40.2

MiddleEast742.7

Europe andEurasia

140.5

NorthAmerica59.5

Africa114.3

Central andSouth America103.5

LOCATION INSIDETHE EARTH

The movements of theEarth's crust subjectedthe strata rich inorganic remains togreat pressure andtransformed them intohard coal over thecourse of 300 millionyears.

FORMATIONOF PETROLEUMIn an anaerobicenvironment at adepth of about 1mile (2 km), organicsediments thatdeveloped inenvironments withlittle oxygen turninto rocks thatproduce crude oil.

KEY

Gas

Petroleum (Oil)

Water

At times, thesurface of anthracitecan appear to havetraces of plantfossils.

ANTHRACITEROCK

SALINE DOMESTRATIGRAPHICTRAP

ANTICLINE FAULT TRAP

PETROLEUM TRAPS

Caprock StorageRock

Marble and QuartziteThese rocks are compacted andnonfoliated. Marble is a thick-grained

crystalline rock, derived from limestone ordolostone. Because of its color andtoughness, marble is used in theconstruction of large buildings. Quartzite is avery hard rock, usually made of sandstonerich in quartz, which, under elevatedmetamorphic conditions, melts like pieces ofglass. Quartzite is normally white, but ironoxide can give it a reddish or pinkish tone.

QUARTZITEIt is hard and tough; it iscompacted because thequartz grains entwine.

7 IS THE LEVEL OFHARDNESS OFQUARTZITE.

RROCKS AND MINERALS 7372 CLASSES OF ROCKS

CommonMetamorphic Rocks

Slates and PhyllitesThese foliated rocks recrystallized undermoderate pressure and temperature

conditions. Slate has very fine grains made of smallmica crystals. It is very useful in the production ofroof tiles, floor tiles, blackboards, and billiard tables.It almost always is formed through low-grademetamorphism in sediments and, less often, fromvolcanic ash. Phyllite represents a gradation inmetamorphism between slate and schist; it iscomposed of very fine mica crystals, such asmuscovite or chlorite.

GneissStriped rock that usually contains long and granularminerals. The most common types are quartz, potash

feldspar, and plagioclase. It can also have smaller amountsof muscovite, biotite, and hornblende. Its characteristicstripes are due to a segregation of light and dark silicates.Gneiss rock, which has a mineral composition similar to thatof granite, is formed through sedimentary processes orderived from igneous rocks. However, it can also formthrough high-grade metamorphism of schists. It is the lastrock of the metamorphic sequence.

Foliation

SLATE Its black color comes fromthe carbon in organic matterpresent in sediments.

SLATE Because of exfoliation, it tendsto break into flat sheets.

HORNBLENDESCHISTIt contains some sodiumas well as considerableamounts of iron andaluminum.

MICACEOUSSCHISTIts characteristic coloring isdetermined by colorless orwhite muscovite crystals.

PHYLLITESimilar to slate, it isnotable for its silky luster.

LAMINATED OR STRIPED TEXTURE,RESULTING FROM THE PRESSURE TOWHICH THE ROCK WAS SUBJECTED

StripesMAKE IT POSSIBLE TO DETERMINETHE DIRECTION IN WHICH PRESSUREWAS EXERTED ON THE ROCK.

0.04 inch(1 mm)OR MORE. THE SIZE OF MICA GRAINS INSCHIST—LARGE ENOUGH TO SEE WITHTHE UNAIDED EYE.

MARBLEIt is highlyvalued for itstexture andcolor. It is usedin sculpture andarchitecture.

GARNETIFEROUS SCHISTThis rock's name comes from itscomponents. Schist determinesits texture and garnet its colorand distinctive features.

SchistThis rock is more prone to foliation, and itcan break off in small sheets. It is more

than 20 percent composed of flat, elongatedminerals, which normally include mica andamphiboles. For schist to be formed, a moreintense metamorphism is needed. The differentschistose rocks' names and characteristicsdepend on the predominant mineral thatcomposes them or on the one that producesexfoliation. Among the most important schistoserocks are mica, hornblende, and talc. Becausethis type of rock has different layers, it has beenused in sculpture.

GARNETIFEROUS SCHISTThe dark red crystals ofgarnet formed duringmetamorphism.

MARBLE MICROGRAPHImpurities and accessoryminerals color the marble.

SLATEMICROGRAPHYComposed of foliated orlaminated clay minerals

GNEISSHeat and pressurecan change graniteinto gneiss.

The classification of metamorphic rocks is not simple because thesame conditions of temperature and pressure do not always producethe same final rock. In the face of this difficulty, these rocks are

divided into two large groups, taking into account that some exhibitfoliation and others do not. During the transformation process, the densityof rock increases, and recrystallization can induce the formation of biggercrystals. This process reorganizes the mineral grains, resulting in laminar orbanded textures. Most rocks derive their color from the minerals of whichthey are composed, but their texture depends on more than just theircomposition.

Incredible Petra


Historians from ancient Rome used to talk about a mysterious city of stone. In 1812 JohannLudwig Burckhardt of Switzerland rediscovered it. Traces of Neolithic civilizationswere found in Petra; however, its foundation in the 4th century BC is

attributed to the Nabataeans, a nomadic people. The Nabataeans weremerchants and raiders who became prosperous by controlling the spicetrade. The city, carved in sandstone, knew times of splendor,but it eventually fell into ruin.

WINGED LIONS (Interpretation)These carvings were located in the templeof Atargatis, goddess of fertility in theNabataean culture.

ELEPHANTS (Interpretation)Native to Africa or India, elephants werenot represented in classic culture. Here,however, they are seen adorning Greek-style capitals. This particular merging ofcultures created expressions found nowhereelse in the ancient world. Archaeologistsfind it difficult to date the pieces of artfound in Petra.

CORINTHIAN CAPITAL (Interpretation)One of the most classic capitals of Greekarchitecture, along with the Ionic and Doricstyles

SERAPISGod of prosperity andconcealed mysteries.In Egyptianiconography, Serapishas horns.

HIDDEN IN THE DESERT

Uncertain OriginsPetra's architecture is dominated byGreek, Egyptian, and Roman features;

however, their symbiosis with Easternelements is so great that to this day expertsfind it difficult to establish Petra's origin anddates of construction. The city's exterioradornments contrast with the interiorsobriety of its temples. It containedsumptuous public baths that date from a timeof splendor (1st century BC). However, mostof Petra's population, which reached a peak of20,000 inhabitants, lived in adobe houses.

Temples and TombsThe only way to reach Petra is by footthrough a narrow passage among the

rocks. The passage is 1 mile (1.5 km) long and, atsome points, less than 3.3 feet (1 m) wide. TheTreasury (Khasneh) is the first seen uponentering the city, followed by a Romanamphitheater. The buildings are carved intocliffs, and more than 3,000 old tombs have beenexcavated. The city also has fortifications.

Carved in StoneThe construction over sandstonerespects and takes advantage of the

characteristics of the landscape. To createopenings, builders used the cracks andfissures that already existed in the rock.The sandstone in Petra is composed of atleast two original types of sediments ofdifferent colors. Some people believe theyare from different geologic phases, but it ismore likely that the original sand was madeof different grains.

A Door Between WorldsThe statue represents the god Serapis, whosecult was established in the 4th century BC in

both Greece and Egypt. Serapis is of Greek origin, butobelisks and cubic stones, typical Egyptian monuments,also abound in Petra. For a long time, it was believedthat Petra was the biblical town of Edom. Its strategiclocation made it a transit area for Indians andAfricans. The Roman and Byzantine empires had aprofound influence: Petra was their gateway to theEast. Beginning in the 7th century, though, Nabataeanculture began to merge with Islamic culture, and itultimately disappeared.

Petra

On the RiftITS CLIFFSARE PART OFTHISFRACTURE; INTHE YEAR 363,IT WASDAMAGED BYANEARTHQUAKE.

The TreasuryIT WAS BELIEVED THAT THIS BUILDING HOUSED A PHARAOH'STREASURE. ITS CUBE-SHAPED INTERIOR HAS SMOOTH WALLSAND IS LINED WITH MORTUARY CHAMBERS.

SANDSTONEA sedimentary rockwith medium-sizedgrains (less than 0.08inch [2 mm]), withgreat toughness andhardness. Itsmineralogicalcomposition can vary.In the Jordaniandesert, it forms cliffs.

TREASURYMOUNT EL KUBHTA

MOUNT UM AL BIERRA

3 MILES (5 KM)

ORIGINALWALLS

BYZANTINEWALLS

CHRISTIANTOMBS

MAINSTREET

HABISCASTLE

GREATTEMPLE

AMPHITHEATER

Tourist AttractionThe stone buildings wereerected at different timesover a period of 1,000 years.

Petra is hidden in the mountains 155 miles(250 km) south of Amman, the capital ofJordan, and north of the Red Sea and theGreat Rift Valley in Africa.

Use of Rocks and Minerals

Human beings have beenextracting coal since ancienttimes, and mining generallytakes place undergroundbecause most veins are

hundreds of feet down. Human beingshave to make incursions into the bowelsof the Earth to extract its wealth. Thematerials extracted from the Earth arethe basis of modern civilization, the raw

material from which many productspeople use are made. Unfortunately, theEarth's reserves of coal, oil, and gas arebeing depleted. For this reason, othersources of energy to replace them are

being sought. One of these alternativesources is nuclear energy. It requiresuranium, an element found in certainrocks.

IN DAILY LIFE 78-79

MOUNTAINS OF GOLD AND SILVER 80-81

AN OPEN-AIR MINE 82-83

BLINDED BY BRILLIANCE 84-85

BLACK AS COAL 86-87

BLACK GOLD 88-89

RADIOACTIVE MINERALS 90-91

FOUND ALL OVER THE WORLDCoal is found in almost all regionsof the world, but today the onlydeposits of commercial importanceare located in Europe, Asia,Australia, and the Americas.

78 USE OF ROCKS AND MINERALS

In Daily Life


Hydrocarbons, the Source of EnergyThe combustion of petroleum derivatives provides energy forpropulsion. The combustion pathway begins with the storage of gas

in the tank and ends with the expulsion of waste gases through theexhaust pipe. There a catalyst with thousands of cells filters the mosttoxic gases: carbon monoxide and nitrogen oxide.

FUELTANK

EXHAUSTPIPE

Electric Properties: Conductors,Insulators, and Semiconductors

Metals, which tend to lose electrons, are the soul of electric cablesand circuits. Nonmetals (and their polymeric derivatives) hinder the

flow of electrons and are used as insulators. Other minerals, such as silicon,have intermediate properties: electronic components are manufactured byadding impurities to modify their properties.

IGNITIONCOILBarium

HEADLIGHTSTungsten TIRES

Vulcanizedsteel mesh

WHEELSTitanium is oftenused in alloys and inthe car's finish.

CIRCUITSGold, silver,palladium

DISTRIBUTORPlatinum

IRON Strong and resistant

LOCKS Covered with zinc

WINDOWS Glass (silica)

ALUMINUM Light and durable

MAGNESIUM Adds flexibility

MIRRORS Glass and lead

0.07pound(0.03 kg)

MORE ALUMINUM ISREQUIRED BY VOLUMEFOR THE SAMEWEIGHT OF STEEL.

20%

NonmetalsSilicon and its derivatives (silicone, silica, and silicates such asasbestos) are omnipresent materials in car manufacturing. They

appear in crystallized form, such as quartz, and in noncrystallized—orglass—form. Other nonmetals aid in the strengthening of metals—forexample, carbon in the production of steel and sulfur in thevulcanization of rubber.

SPARK PLUGSPorcelain(kaolin)

STEERINGWHEELSilicon coating

ENGINE JOINTSAsbestos

BODYWORKAluminum, titanium,magnesium, and steel

PER CUBIC INCHMAGNESIUM IS THELIGHTEST METAL USED FORINDUSTRIAL PURPOSES.

ENGINE BLOCKIt sustains theengine and is madeof magnetite, aniron ore.

ENGINEAluminumMagnesiumIronCobalt

MetalsThe body of a car is made of iron (present in bothsteel and magnetite), aluminum, and magnesium.

Other metals are used to produce parts that are resistantto torsion (vanadium, cadmium), temperature (cobalt),and corrosion (nickel and zinc). Barium and platinum areused in very specific parts, and other metals are used insmaller amounts in lubricants, fluids, or paints.

WIRING SYSTEMCopper

SPRINGSCadmium

SEAT

SPRINGSSteel

It is impossible to conceive of modern life without the constant use of objects andmaterials made of rocks and minerals, metallic or nonmetallic. To illustrate this,it is enough simply to consider the elements that make up a car, trace them

back to their origins, and consider the processes that shaped them. In some cases,the texture and characteristics of each material can be easily seen. Othermaterials, especially nonmetals such as coal and sulfur, are less noticeable, butthey are a part of the production process as well.This process tends to emphasize and improve thephysical, chemical, and electric characteristicsof each material.

BACK Glass fiber

CONTROL PANELIn smaller contact areas, more expensivemetals are used (gold is the best conductor).Chips and other electronic componentscontain silicon. Phosphorescent displayshave strontium paint.

DISPLAYSStrontium


From the decision to exploit an area where valuable minerals are suspected to exist to obtainingthese minerals in major amounts, large-scale mining operations require complex work that lastsfor years. For instance, the exploitation of Veladero, an open-air gold-and-silver mine located in

the province of San Juan in the Argentinean Andes and exploited by the Canadian companyBarrick Gold, required more than a decade of research and development before the firstingots were obtained in October 2005. To reach the deposits, roads and housing werebuilt for the workers. The potential environmental impact of the mine wasanalyzed since explosives had to be used and toxic substances, suchas cyanide, were needed for extracting and separating therock from other metals.

Mountains of Gold and Silver


PROSPECTING1 TO 3 YEARS COST: $10 MILLIONProspecting began in 1994. During this

phase, the possible existence of a deposit

covering a vast area was analyzed. It was

necessary to draw maps, conduct studies,

make satellite images, and undertake field

trips to analyze superficial rocks.

1.

2.

BLUEPRINT OF THE MINE2 TO 5 YEARS COST: $547 MILLIONOnce the reserves and costs wereanalyzed, it was necessary to open themineral deposit and evaluate theenvironmental impact of the operation.The infrastructure was then built; itincluded paths, houses, and riverdiversions.

3.

EXPLOITATION2 TO 5 YEARS COST: $90 MILLIONThe first phases are involved with field prospecting. During thisprocess, preliminary research is confirmed or revised. Once theexistence of the deposit is confirmed, the next step is toestablish its dimensions, reserves, yield, and extraction costs.

VELADERO,ARGENTINALatitude 29° S

Longitude 70° W

Total land area

Employed builders (peak)

Gold reserves (1st estimate)

Estimated life span

5,000

900 tons

17 years

1,158 square miles(3,000 sq km)

GRINDINGSYSTEM

MACHINERYWAREHOUSEWith capacity tostore big vehicles

Leaching Ground (Potrerillos Ravine)HERE GOLD IS SEPARATEDFROM THE ROCKS.

GOLD IS NOT FOUND INMETALLIC FORM BUTRATHER COMBINED WITHOTHER MINERALS.

OPEN CUT II(AMABLE EDGE)

OPEN CUT I(FEDERICO EDGE)

VELADEROHILL

VELADEROMINE

EXPLORATORYPERFORATION

VISUALANALYSISOF ROCKS

PROCESSINGPLANT

SAN JUAN

ABOVE SEA LEVEL The elevation of the mine

(4,000 m)

13,120feet

STRATA Based on these features,geologic maps of thearea are drawn. DIRECT OBSERVATION

Geologists visit the areaand take rock samples.

SUPERFICIAL ROCKSDuring prospecting, fieldsamples are collected foranalysis.

FEASIBLE AREAOpened by meansof perforations andexplosions

NONPRODUCTIVEAREA Areas that do notyield satisfactorymining results

MINERALCONCENTRATIONis evaluated bytaking samples fromdeep in the Earth.

PERFORATIONTOWERUsed to extract rockslocated deep withinthe Earth

ENCAMPMENTSturdy buildingsat 12,470 feet(3,800 m) abovesea level

164 FEET (50 M)

HUGE OPEN-AIR MINEVeladero—located in the Argentinean province of San Juan, as shown on the map—required 2,300tons of metallic structures and consumes 2,520tons of sodium cyanide per year for extracting gold.


There are many types of mines. Some are located in the depths ofthe Earth, and some show their contents at its surface. BinghamCanyon, a copper mine located in Utah, is not only one of the

most important open-air mines but also one of the largest excavationsin the world. It is so large that it can be seen from space. It has been inoperation since 1903, and it has been excavated in the form of terraces,like those used in agriculture. Its activity never stops, continuing even onweekends and holidays. The manner in which copper is extracted involvesnot only the use of machinery of extraordinary dimensions but also theuse of a hydro-metallurgic chemical process called lixiviation, or leaching.Thanks to this process it is possible to obtain 99.9 percent of copper in itspure state from a copper concentration of 0.02 ounce per pound (0.56 gramper kg) of raw material.


1

2

3

How the Metal Is Extracted

TERRACING OF THESURFACEThe mine acquires a steplikeshape because it is excavatedin spiral terraces. Themachines can move easilyover the terraces, collectingthe extracted material.

PATHSThe roads are well built, and they canwithstand loads of up to 1,765 cubicfeet (50 cu m) of rock on only one truck.

LOADERS/CHARGERS

TUNEL

RAW MATERIALThe material extractedfrom the pit is loadedon a mobile grinder.

TRANSMISSION PULLEYS

SPRINKLERS

COLECTOR

SEWER ACID SOLUTION

26 FEET(8 M)

2.5 MILES (4 KM)

0.4 MILE(0.7 KM)

ELECTROLYTIC POOL

COPPER

SHEETS

BOTTOM OF THE MINE

TERRACES

MAXIMUM PHREATIC LEVEL

BINGHAMCANYONUNITEDSTATESLatitude 40° 32´ N

Longitude 112° 9´ W

Diameter of the pit

Depth of the pit

Opening year

Closing year

Number of employees

2.5 miles (4 km)

2,300 feet (700 m)

1903

2013

1,700

HOW MATERIALIS OBTAINEDThe process begins with rock perforationand blasting. The rock is removed from thepit and loaded by large shovels onto trucks.Then it is unloaded onto a mobile grinder.The ground rock is removed from the mineon conveyor belts and then sprayed with asolution of water and sulfuric acid.

ARRANGEMENT OFTHE STACKWhen on the conveyor belts, the materialis taken to a place where it will form alixiviation pile or stack, and a trickleirrigation system is installed on top of thispile. Sprinklers cover the entire exposedarea. The material will spend 45 days here.

COPPER RECOVERYThe resulting copper solution is collected in conduitsand then undergoes a process of electrolytic refining.During this process, electricity passes between twocopper plates suspended in the solution; copper fromthe solution adheres to the sheets as it is separatedthrough electrolysis.6 ounces/

gallon (45 g/l)OF COPPER IN THE SOLUTIONAT THE END OF THELIXIVIATION PROCESS

COPPER CONCENTRATIONIN THE RAW MATERIAL

0.56 %

99.9 %COPPER IN A PURE STATE

FORMATION OF THE MINESurface mines take the shape of large terracedpits, which grow ever deeper and wider. Viewedfrom above, an enormous spiraling hollow can beseen. This is a relatively inexpensive and simplemethod to extract high-purity materials.

LIXIVIATIONThe hydro-metallurgic process that makesit possible to obtain copper from theoxidized minerals by applying a solution ofsulfuric acid and water. Oxidized mineralsare sensitive to attack by acid solutions.

Thousands of pounds of explosives, trucks and shovels aslarge as a house, and massive grinding machines that can

reduce hard rocks to dust are involved in the extraction process,and rock temperatures are raised to 4,500° F (2,500° C). In thisway, copper is extracted from one of the largest open-air mineson the planet. The raw material excavated from the terraces inthe mine contains oxidized copper minerals. This material is

transported to grinders, which produce rock fragments 1.5 inches(4 cm) in diameter. These materials are placed in a pile that istreated with a solution of water and sulfuric acid. This process iscalled lixiviation, or leaching. Lixiviation is a hydro-metallurgictreatment that makes it possible to obtain copper present in theoxidized minerals. The treated material begins the process ofsulfatation of copper contained in the oxidized minerals.

WATER BASINThe phreatic layer, theclosest aquifer to thesurface below the watertable, emerges at thebottom and forms a waterbasin with a peculiar colorbecause of the copper saltsin the deposit.

An Open-Air Mine


Blinded by Brilliance


UNITEDSTATESCalifornia

Sacramento River

11848On the morning of January 24, whileJames Marshall was building a sawmillfor his employer John Sutter, hediscovered gold on the banks of theSacramento River. This irrevocablychanged the history of California.

2 31850California became the 31st state of the Union. Slavery wasabolished because of the large influx of immigrants and thefear that it would reduce workers' salaries. However, theFugitive Slave Act was sanctioned by the state. Accordingto this law, every fugitive slave that entered California hadto be returned to his or her owner.

1852When the surface gold was exhausted, morecomplex technology was required to extractit from the ground. Hydraulic mining, whichused water jets, was a technique used forthis purpose. Miners then becameemployees, enduring long workdays.

PARTICLESBEING WASHED

WASHEDPARTICLES

DRAGGINGMules dragged large stones, usedto break other quartz stones,thus releasing the gold within.

SLOPEThe water flowedand depositedgold at theserrated bottom.

SLUICE BOXWater flowed through the artificialcanal, where riffles (barriers) alongthe bottom of the sluice box caughtthe gold and let the other materialpass through.

THEYSHOVELEDTHE GRAVEL.

CHINESEChinese immigrants,attracted by theprospect of wealth,constituted most ofthe labor force.

PANThe swirling movement ofthe pan allowed for theseparation of sediments, andthe gold could be identifiedby a difference in weight. DRY RIVER

In 1853, $3 million wasinvested to change thecourse of the Yuba River,which merged with theSacramento River. Thewater of the new canalwas used to wash the gold.

GOLD IN THE SOILGold could be found indry riverbeds as dust,as nuggets, or as smallrock fragments.

HOPPERThe gravel was placed in thehopper and the depositedmaterial was moved with alever. When water wasadded, the dirt could becarried away, leaving thegold at the barrier since thedensity of gold is greaterthan that of water.

RETURN TO THE RIVEROnce the water had beenused to pan for gold, it waschanneled back into theriver from which it came.

ARTIFICIALCANAL

BY HANDResources and tools werescarce. Almost everything wasdone by hand.

ENCAMPMENTSBad living conditionsled to the death ofmany workers;many were alsokilled by epidemicsand illnesses.

DRYRIVERBED

CHANNELEDRIVER

DRYRIVERBED

FLOW OFIMMIGRANTSIn 1848, California had apopulation of 14,000.However, within four yearsand with the gold fever atits peak, the populationrose to 223,856.

RÍO SACRAMENTO

100SLUICE BOXES COULD BEUSED IN THE CONSTRUCTIONOF JUST ONE WASHER.

$500MILLION IN GOLD WASEXCHANGED DURINGTHE ENTIRE DECADE.

$16WAS THE PRICE OF A PLOTOF LAND; 18 MONTHS LATER,IT WAS PRICED AT $45,000.

GOLDSELECTOR

ORIGINALRIVERBED

By Boat40,000*

Through Mexico15,000

From the United States30,000

Key *Number ofimmigrants whoarrived in 1849

WASHINGCONTAINERS

The discovery of gold in the Sacramento River in California in the mid-19th century started one ofthe largest migrations of its time. Fortune hunters came from the Americas as well as from Asia,but few were able to achieve their goal of striking it rich. Each year, obtaining gold required a

larger investment of time and equipment, and equipment supplierswere the ones who ultimately earned the highest profits. Goldwas the key force in settling California, now thewealthiest state in the United States. At its peak,immigration overwhelmed the state's social andmunicipal services as up to 30 houses werebeing built each day.

OF EXPLOITATION ISCARRIED OUT UNDERGROUND.

60%Black as Coal

86 USE OF ROCKS AND MINERALS ROCKS AND MINERALS 87

In gallery or subterranean mines people must enter the bowels of the Earth to be able to extractthe planet's mineral wealth. Some mines for extracting coal—the legendary driving force of theIndustrial Revolution—are a clear example of this type of exploitation. Although these mines

imply higher costs and labor risks, they have a lower environmental impact.

2. EXTRACTIONThe method that is widelyused is that of continuousmining. A machine extractsthe coal mechanically.

3. TRANSPORTATIONThe extracted coal is placed onthe conveyor belts that take itto the main shaft, and fromthere it is taken to the surface.

4. ELEVATIONFrom the main shaft,the coal istransferred to cargoelevators thattransport it to thesurface.

6. DISTRIBUTIONMine trains transport the coal from themine to the point of consumption.

5. WASHING AND CLASSIFICATIONCoal that leaves the mine is mixed with mudand rocks. It must be washed and classifiedaccording to quality and size.

How Coal Is Extracted

1.8 tonsIS THE AMOUNT OF

COAL THE PERFORATOR

EXTRACTS IN AN HOUR.

5,000 feet(1.52 km)THE SHAFTS CAN REACH

THIS DEPTH.

Year 2003. In millions of tons.MAIN PRODUCERS

1. PERFORATIONA vertical shaft isperforated,allowing access tothe coal vein.

GALLERYTunnel that is used forcommunication in the mine

FRESH-AIRENTRANCE

EXIT FORCONTAMINATED AIR

CARGOELEVATOR

MAIN SHAFT

SECONDARYSHAFT

16 TO 23 FEET(5 TO 7 M)

EXTRACTIONTOWER

1,6351,070

503294264

Year 2003. In millions of tons.MAIN CONSUMERS

China

United States

India

Germany

South Africa

1,5311,094

430273264

VENTILATIONWithout goodventilation, methane,an explosive gas,condenses in thegalleries and createsthe risk of explosions.

MINER'STRANSPORT

MOVEMENT INTHE GALLERIESThe miners travelon foot or by trainto the coal vein.

TRANSPORTERBELT

Coal Vein

Coal is separatedfrom other materialsthrough decantation.

MobileArm

Coal withimpurities

Coal

Coaldust

Coalpellets

Coal gravel

Water

Impurities

WASHING ANDCLASSIFICATIONBUILDING

China

United States

India

Russia

South Africa

How Petroleum Is Obtained

1.SEARCHIndirect methods are usedto detect the presence ofhydrocarbons. However, theinformation obtained is notconclusive.

2.EXPLORATIONOnce a deposit is detected,the soil is drilled to verifythat there is petroleumwith economic potential.

3. EXTRACTIONIf the well is productive,the drilling towers areremoved and extractionsystems are installed.

4. TRANSPORTATIONTankers transportcrude oil to therefinery, wherevarious products canbe derived from it.

GAS

LUTITE

PETROLEUM

SEISMIC TRUCKThese machines are locatedat different points withinthe research area.

MiddleEast

Pool forRecovering DrillMud

Electric Motors

1 DRILLINGPowerful motorsmake the drillingstring turn.

2 DRILL BITIt advances throughthe rock formationsthat lie between thesurface and thehydrocarbons below.

3 CAUTIONOnce oil is detected,the drilling proceedsmore slowly, andvalves are closed toprevent the oil fromgushing to the surfaceunder high pressure.

SeismicWavespenetrate thelayers of theEarth's crustand bounceback to thesurface whenthe type ofrock they passthroughchanges.

VibratingSheet

GEOPHONE

Bounced WavesGeophonesregister thesewaves. Aseismic sectionis generatedbased on thedata obtained.

Pipe forDelivering Drill Mud

PUMP ENGINE

Pumping systemsIf oil does not flownaturally, it is extractedwith a pumping system.

WATER

TANKER

Because of its economic importance as a source of energy, petroleum, oroil, is called black gold. Searching for it requires large amounts of moneyand years of investigation and exploration, all with no guarantees. Once

discovered, petroleum extraction entails the use of expensive machinery, whichincludes everything from oil pumps to refineries that convert oil into manyderivative products. The oil trade is one of the most lucrative businessesworldwide, and a change in its price can affect national economies and putwhole countries on guard. Petroleum is a nonrenewable source of energy.

5. REFINING The components ofcrude oil areseparated, makinguse of the fact thateach componentboils at a differenttemperature.Refining is carriedout by means of twomain processes:fractional distillationand cracking.

1 INJECTIONOF GAS ORWATERis carried outunder highpressure; thenaturalvolume isincreased.

2 RISINGPETROLEUMThe injectedmaterialpushes up thepetroleumand makes itrise faster.

29.6%

Europe and Eurasia22.1%

NorthAmerica 18.2 %

Africa10.8%

Pacific-Asia 10.2%

Centraland SouthAmerica9.2%

NorthAmerica

MAIN CONSUMERSYear: 2004

30.1%

Pacific-Asia28.8%

EuropeandEurasia25.9%

Central and South America6.0%

Middle East5.9%

Africa3.3%

FRACTIONALDISTILLATION

CrudeOil

LightMolecules

Molecules ofIntermediateWeight

HydrocarbonMolecules

CRACKINGBig molecules are brokendown to create smaller ones.

DistillationColumn

Heat

PRODUCTS OFDISTILLATION

Gas

Gasoline

Kerosene

Diesel Oil

Fuel Oil

Residue

ApproximateBoiling Point

212º F(100º C)

392º F(200º C)

572º F(300º C)

REFINERY

FractioningColumns

CatalyticCrackingPlant

Crude-OilDeposit

DrillingColumn orString This pipe willbe lowered intothe ground.

MachineryRoom

Cargo space dividedinto compartments

25%of the world'smerchant fleet was used totransport oil. Therewere 11,356 tankers.

By January 2005

NATURAL WAYS TOPUMP PETROLEUM

The drivingforce is thegas dissolvedin a petroleumdeposit.

The gasaccumulatedin the depositpushes thepetroleumoutward.

Later as wateris pumped in,it accumulatesunderneaththe petroleumand pushes itupward.

Oil Pump

SEA

CONTINENTALCRUST

IMPROVEMENTIN OIL RECOVERY

CONTINENTALCRUST

SOLIDROCK

North America and Pacific-Asia account for 90 percent of the increase in petroleumconsumption over the last 10 years.

SmallerMolecules

Detail ofthe Drill Bit DRILL MUD

flows downthrough thepipe and exitsthrough thedrill orifices.

As the mudrises, it carriesrock thatreveals whichstrata havebeen perforated.

EXPLORATORYWELL

SolidRock

RollerwithTeeth

77%

MAIN EXTRACTORSYear: 2004

OF ALL PETROLEUMPRODUCED ISEXTRACTED FROMUNDERGROUNDDEPOSITS.

Black Gold



Uranium and plutonium were used for the first time—for militarypurposes—in the 1940s. Once World War II ended, nuclearreactors and their fuels began to be used as sources of energy. To

process these minerals, nuclear plants are necessary. They must be builtfollowing many safety guidelines, since nuclear energy is considered to bevery risky. Accidents like the one in Chernobyl and, more recently, inTokaimura, Japan, are clear examples of what can happen when control ofthis form of energy is lost. These images show the structure and heart ofa nuclear reactor, the way uranium is processed, and the peaceful uses ofthis type of energy.

FUEL RODS IN EACH GROUP

264

THE NUCLEUS OF THE REACTORis in the lower part of the safety vessel, in whichthere are about 200 groups of fuel sheaths sized 0.4inch (1 cm) in diameter and 13 feet (4 m) in height.

USE OF URANIUM IN MEDICINEThe application of nuclear energy helps with thediagnosis and treatment of diseases such as cancer.It can detect alterations long before symptomsdevelop clinically, which allows for more effectiveearly treatment.

REACTOR BUILDINGThis special building is made of reinforcedconcrete and steel. It is 210 feet (64 m) highand 148 feet (45 m) wide. It houses andshelters the components of the reactor. It alsocontains the pressure vessel, four steamgenerators, a pump (which circulates coolingwater around the core), and a compressor(which keeps the water under pressure).

URANIUM HANDLINGUranium 235 is the only isotope that is found in a naturalstate, easily fissionable. For this reason, it is the main fuelused in nuclear power plants. Even though it is rare to findit in the Earth's crust, it can be found in enriching depositsin watercourse beds.

Radioactive Minerals

PROTECTIONGLOVES

RAWURANIUM

GROUPS OF FUEL RODS THATGENERATE THENUCLEAR REACTION

CONTROLRODS

HumanScale

WATERDEPOSIT

WATERURANIUMPELLETS FORUSE IN AFUEL ROD

Pressure Vessel The nuclear reactor is inserted into a vessel formed bysteel that is approximately 1.6 feet (0.5 m) thick. The fuel,

which is encapsulated in zirconium alloy sheaths, is located insidethe hollow space of the vessel. This design helps to meet one ofthe first goals in nuclear safety: to prevent radioactive productsfrom leaking into the surrounding environment.

Carbon 14is a method for dating organic fossilsamples based on the exponential decay

law of radioactive isotopes. After a livingorganism has been dead for 5,730 years, theamount of 14C present in its body hasdecreased by half. Thus, when the amount oflatent 14C is measured in organic materials, itis possible to calculate the amount remainingin the material and, therefore, to calculatewhen the organism died.

PIPINGTUNNEL

CONTAINER FORTHE FUEL RODS

COOLING-FLUID PUMP

CRANEBRIDGE

CRANE FORTHE FUEL RODS

HOOKS TO LIFTOR LOWER THECONTROL RODS

MACHINERYROOM

PIPINGTUNNEL

STEAMGENERATOR

STEELSTRUCTURE

THYROID TAKES IN 99MTC-PERTECNETATE.

MAMMOTHCUB

THYROIDSCINTILLOGRAPHYUSING POSITRONEMISSION TOMOGRAPHY

THE TEMPERATURE OFTHE WATER PELLET

572º F (300º C)

REINFORCEDCONCRETEWALL

REINFORCEDCONCRETEWALL

SAFETY SUITTo handle radioactive material, such as spent fuelbars, workers must wear a special suit becauseof the high levels of radiation.

THE HANDS MUST BEPROTECTED WITHINSULATING GLOVES.

THE WORKER CARRIESAN OXYGEN TANK. AHOSE IS CONNECTED TO THE TANK SO THEWORKER CAN BREATHE.

THE SUIT IS HERMETIC. ITMUST ISOLATE THE WORKERFROM THE OUTSIDE.

50,000 years

UR

AN

IUM

RO

DS

REACTORCORE

92 GLOSSARY ROCKS AND MINERALS 93

Glossary

AlkalinesMinerals that have a high content of potassium,sodium, lithium, rubidium, and calcium.

AmorphousMineral with fractured surfaces instead ofcrystalline faces. Noncrystalline.

AnticlineA fold of sedimentary strata sloping upwardslike an arch.

AsthenosphereLayer inside the Earth, below the lithosphere. Itis part of the upper mantle and is composed ofeasily deformable rock.

AtomThe smallest unit of matter.

BacteriaMicroscopic and unicellular life-form found inair, water, plants, animals, and on the Earth'scrust.

BatholithGreat mass (larger than 60 square miles [100sq km] of surface) of intrusive igneous rocks.

Bravais LatticesThree-dimensional crystal systems, based oncertain mathematical principles, that representthe 14 types of cell units.

ButteHill with a flat top and sloping sides, found inareas that have undergone intense erosion.

CanyonDeep, narrow valley formed by fluvial erosion.

CaratUnit of weight used in jewelry, variable in timeand place, equivalent to 0.007 ounce (0.2 g).

CaveSubterranean cavity formed through thechemical action of water on soluble, generallycalcareous, ground.

CementationProcess by which sediment both loses porosityand is lithified through the chemicalprecipitation of material in the spaces betweenthe grains.

Cementation ZonePlace where lithification occurs. Waterinfiltrates the area, fills up the spaces betweenthe grains of sediment, and transforms loosesediment into a solid mass.

Chasm, or RiftWide valley formed as a consequence of theextension of the crust at the boundaries ofdiverging tectonic plates.

Chemical CompoundSubstance formed by more than one element.

Chemical ElementSubstance that contains only one type of atom.

ClayFine-grained sediments formed by the chemicaldecomposition of some rocks. It is malleablewhen wet and hardens as it dries.

CoalCombustible black rock of organic origin. It isproduced through the decomposition of plantmaterials that accumulate in swamps orshallow marine waters.

deposit is called primary. Otherwise, it is calledsecondary.

DiatomiteLight, porous rock. It has a light color, and it isconsolidated. Composed exclusively (or almost)of diatoms.

DolostoneCarbonated sedimentary rock that contains atleast 50 percent or more carbonate, of which atleast half appears as dolomite.

EarthquakeThe sudden and violent release of energy andvibrations in the Earth that generally occursalong the edges of tectonic plates.

ElasticityTendency of a mineral to recover its shape afterbeing subjected to flexion or torsion.

EraDivision of time in the Earth's history. Geologistsdivide eras into periods.

ErosionRemoval and transport of sediment through theaction of water, ice, and wind.

EvaporationProcess through which a liquid becomes gaswithout boiling.

ExfoliationThe tendency for certain minerals to fracturealong regular planes within their crystallinestructure.

FaultFracture involving the shifting of one rock masswith respect to another.

FlexibilityAbility of minerals to bend without fracturing.

FluorescenceProperty of some minerals that enables them toemit a certain level of light when exposed toultraviolet rays. The fluorescent propertiespresent in a metal can make it look as if it weretruly fluorescent.

FoldBending and deformation of rock strata due tothe compression caused by the movements oftectonic plates.

FossilAny trace of an old life-form. It can be thepetrified remains of an organism or animpression of an organism left in rock.

Fossil FuelFuel formed from the partially decomposedremains of deceased organisms. Thesemixtures of organic compounds are extractedfrom the subsoil with the goal of producingenergy through combustion. They are coal, oil,and natural gas.

FractureBreak of a mineral along an irregular surface. Itcan be conchoidal, hooked, smooth, or earthy.

GemMineral or other natural material that is valuedfor its beauty and rarity. It can be polished andcut to produce jewels.

GeodeSpherical, rocky cavity covered with well-formed crystals.

GeologyStudy of the Earth, its shape, and its composition.

Rocks, minerals, and fossils offer information thathelps us reconstruct the history of the planet.

GlacierA large mass of ice formed through theaccumulation of recrystallized and compactedsnow occurring either on a mountain or over alarge area on a landmass. Ice moves slowly andboth excavates rock and carries debris.

GraniteIntrusive igneous rock composed mainly of quartzand feldspar. It can be polished and used indecoration.

HabitExternal aspect of a crystal that reflects itspredominant shape.

HardnessResistance offered by a mineral to scratchingand abrasion. One mineral is said to be harderthan another if the former can scratch thelatter.

Hot SpotPlace within a tectonic plate where activevolcanoes form.

HydrothermalProcess involving the physical and chemicaltransformations suffered by rocks or mineralsthrough the action of hot fluids (water andgases) associated with a magma body.

Igneous RocksRocks formed directly from the cooling ofmagma. If they solidify inside the crust, they aresaid to be plutonic (or intrusive); if they solidifyon the surface, they are said to be volcanic (orextrusive).

Impermeable RockRock through which liquids cannot be filtered.

ConcretionHard mass of mineral material that usually holdsa fossil inside.

Contact MetamorphismLarge-scale transformation of a rock intoanother type of rock. This happens mostly as aconsequence of a sudden temperature increase.

Convection CurrentsMoving pathways of material that occur insidethe mantle as a consequence of the transfer ofheat coming from the Earth's core. The hottestzones of the mantle rise, and the coldest onessink. These movements are probably responsiblefor the movement of tectonic plates.

CrackFissure or cavity in the rock that results fromtension. It can be completely or partially filledwith minerals.

CrustExternal layer of the Earth. There are two typesof crust: continental crust forms large terrestrialmasses, and oceanic crust forms the bottoms ofthe oceans.

CrystalOrganized, regular, and periodically repeatedarrangement of atoms.

Crystalline SystemIt includes all crystals that can be related to thesame set of symmetric elements.

DensityAmount of mass of a mineral per unit of volume.

DepositA natural accumulation of a rock or mineral. If itis located at the site where it formed, the

94 GLOSSARY ROCKS AND MINERALS 95

IntrusionA large mass of rock that forms in emptyspaces underground when magma infiltratesstrata, cools, and solidifies.

JadeWhite or green metamorphic rock formed by acompact and tenacious filter of very fine needlesof tremolite. It is a rare rock used in art objects.

Karst CycleFormation cycle of caves that lasts a total ofabout one million years.

KimberliteType of rock usually associated with diamondsand other minerals coming from the depths ofthe Earth.

LavaMagma expelled on the surface of the Earth.

LimestoneRock containing at least 50% calcite. It can alsohave dolomite, aragonite, and siderite.

LithosphereExterior, rigid layer of the Earth formed by thecrust and upper mantle.

LodeSub-superficial rock intrusion of tabular-shapedrock.

LusterLevel of light reflection on the surface of acrystal.

MagmaHot, rocky material from the crust and uppermantle in liquid state that forms crystals as itcools. When magma is expelled at the Earth'ssurface, it is called lava.

Magmatic RockRock that forms when magma cools off andsolidifies. Magmatic intrusive rocks solidifyunderground, while the extrusive ones solidifyon the surface.

MagnetismProperty of some minerals that allows them tobe attracted by a magnet and to change thedirection of a compass needle.

MalleabilityMechanical property of a mineral that makes itpossible for the mineral to be molded andformed into a sheet through repeated blowswithout breaking.

MantleThe layer between the crust and external core.It includes the upper mantle and lower mantle.

MarbleMetamorphosed limestone rock composed ofcompacted calcite and dolomite. It can bepolished.

MassiveOne of the possible habits of a consistentmineral that refers to the tendency for certaincrystals to intertwine and form a solid massrather than independent crystals.

MetalAny element that shines, conducts electricity,and is malleable.

Metamorphic RockType of rock resulting from the application ofhigh pressure and temperature on igneous andsedimentary rocks.

MineralInorganic solid of natural origin that has anorganized atomic structure.

PlacerMineral concentrations as deposits of placerduring time lapses that vary from a few decadesup to millions of years.

PyroelectricProperty that some nonconductor minerals haveto create difference in power transmissionsfrom differences in temperature.

QuartziteMetamorphic rock formed by the consolidationof quartz sandstone. It is extremely hard.Quartzite can also be a sedimentary rock, whichis sandstone with a very high content of quartz;it is very hard and it has light color.

Regional MetamorphismMetamorphism occurring in rock over largeareas.

RockNatural aggregate of one or more minerals(sometimes including noncrystalline substances)that constitute an independent geologic unit.

Sedimentary RockRock that forms through accumulation ofsediments that, when subjected to physical andchemical processes, result in a compacted andconsolidated material. Sediment can form onriver banks, at the bottom of precipices, invalleys, lakes, and seas. Sedimentary rockaccumulates in successive layers, or strata.

SedimentsRock fragments or remains of plants or animalsdeposited at the bottom of rivers, lakes, oroceans by water, wind, or ice.

Seismic WavesElastic waves that travel through the Earthafter an earthquake. They can also be producedartificially through explosions.

SilicatesThey make up about 95 percent of the Earth'scrust. Their tetrahedral structure, with onesilicon and four oxygen ions, creates differenttypes of configurations through the union of theions. According to their composition, membersof this mineral group are differentiated intolight and dark.

SlateBluish black, fine-grained metamorphic rock. Itcan be easily divided into sheets.

SolutionMixture of two or more chemical substances. Itcan be liquid, solid, or gaseous.

StalactiteInternal structure of a cave. It is conical andhangs from the cave ceiling.

StalagmiteInternal structure of a cave. It is conical andrises from the cave floor.

StreakCharacteristic color of the fine dust obtainedfrom a mineral by rubbing it over an unglazedporcelain plate.

Streak TestA test that involves rubbing a mineral againstan unglazed white porcelain sheet to obtaindust. The color of the dust left on the tile canhelp identify the mineral.

Symmetry AxesSymmetry element that enables the repetitionof crystalline faces to form different shapes.

SynclineConcave fold of sedimentary rock strata. Theyounger rocks are located at the center of theconcave.

Talus SlopeAccumulation of fragments resulting from themechanical weathering of rocks. The sedimentdeposit forms more or less in situ as the resultof the transport of materials through gravityover a small distance.

Tectonic ElevationRising of rocks as a consequence of themovements of tectonic plates.

Tectonic PlatesRigid fragments of the lithosphere that move onthe asthenosphere.

TenacityThe level of toughness that a mineral offers tofracture, deformation, crushing, bending, orpulverization.

TransparentIt is said that a mineral is clear when light goesthrough it without weakening. When only somelight passes through, the mineral is calledtranslucent. If no light passes through, it iscalled opaque.

VeinFracture that cuts through rocks and is filled bysome mineral.

Volcanic Outcropping Isolated pile of hard magmatic rocks thatremain after the disappearance of the rest ofthe volcano due to erosion.

WeatheringThe breaking down of a material by sustainedphysical or chemical processes.

Mohs ScaleA tool designed to test the hardness of a givenmineral by comparing it to 10 known minerals,from the softest to the hardest. Each mineralcan be scratched by those following it.

MoleculeChemical compound formed when one or severaltypes of atoms are joined together.

Native ElementAn element that occurs in nature that is notcombined with other elements. Sulfur and goldare examples of native elements.

Oceanic TrenchNarrow and deep submarine depression formedwhen the oceanic crust of one tectonic platemoves beneath another.

Ornamental StoneIt is not a precious stone, but it can be used injewelry or for other ornamental purposes.

OutcropPart of a rock formation devoid of vegetation orsoil that stands out from the Earth's surface.

Oxidation ZoneDeposit of minerals with oxidizing properties,formed through the effect of meteorization orweathering.

PetrifactionCell-by-cell replacement of organic matter, suchas bones or wood, with minerals of thesurrounding solutions.

PiezoelectricProperty that some minerals have to produce adifference in potential when subjected tocompression, traction, or torsion.

96 INDEX ROCKS AND MINERALS 97

Index

Aabrasion platform, 49agate, 23

crystallizing pattern, 43Alexander the Great, Valley of Diamonds, 35allochromatic mineral, 22Allosaurus, 10alloy, 39Alps, formation, 10aluminum, 79amethyst, 22

color, 33ammonia, covalent bond, 28ammonite, extinction, 10Andes mountain range, formation, 11angiosperm, 10anhydrite, 39anion, 28anthracite, 71apatite, 38

hardness, 24Appalachian Mountains, formation, 9aragonite, chemical crystallization, 21Argentina, Veladero mine, 80-81arkose (sandstone), 69ash cone, 43Asscher, Joseph, 35asthenosphere (Earth's mantle), 11atom, crystalline structures, 28, 29augite, 36aureole, 55Australia, Uluru-Kata Tjuta National Park,

58-59automobile: See carAyers, Henry, 59Ayers Rock (Australia): See Uluru-Kata Tjuta

National Park

BBaltica, Ural Mountains formation, 9

barytine, 39basalt, 43

eruptions, 9formation, 12, 65

batholith, 16, 42, 43Yosemite National Park, 44

bauxite, 38beach, formation, 49bedrock, 57Bering Strait, modern humans, 11Bingham Canyon (Utah, United States), 82-83biotite, 37birefringent mineral, 23bismuth, 20Black Stone of the Ka'bah (Mecca, Saudi

Arabia), 59blackboard chalk, 68Borena (ethnic group), 27Bowen's reaction series, 43Bravais, Auguste, 30Bravais lattices, 30brazilianite, crystalline system, 30breccia, 69Bridal Veil Falls (Yosemite National Park,

United States), 45Burkhardt, Jean L., 74

Ccalcite, 66

chemical crystallization, 21hardness, 24

calcium sulfate, 39caldera, 43Caledonian range, 9California (United States), gold rush, 84-85Cambrian explosion, 9Cambrian Period, 9Cango Caves (South Africa), 50-51canyon

Bingham Canyon, 82-83formation, 46, 51

conglomerate (sedimentary rock), 69contact metamorphism, 55

See also metamorphismcopper, 38

mining, 82-83coquina, 66coral reef, 66-67Corkscrew Canyon (Arizona, United States),

6-7, 14-15corundum, hardness, 25covalent bond, 28Cretaceous Period, 10crystal

atomic model, 29Bravais lattices, 30characterization, 30crystallographic axes, 31crystallographic chemistry, 28formation, 63internal network, 29precious stones, 32

crystalline network, categorization, 30crystalline system, 30-31crystallization system, 21crystallographic axis, 31crystallographic chemistry, 28crystallography, 28cubic crystalline system, 30Cullinan diamond, 35

DDallol volcano (Ethiopia), 18-19, 26-27deflation, geologic processes, 46delta, formation, 48dendrite, 38density (mineral), 25desert, 46desertic soil, 56detrital rock, 68-69Devonian Period, 9diamond, 19, 32-33

cuts, 33hardness, 21, 25history, 34-35structure, 21, 30, 33

dike, 42, 43, 65dinosaur, mass extinctions, 10dolomite, 66dune, erosion, 46dynamic metamorphism, 54

See also metamorphism

EEarth

history, 4-5, 8-9layers, 11

earthquake, causes, 13Earth's core, 9, 11, 42Earth's crust, 8, 11, 42Earth's mantle, 11, 42earthworm, humus production, 57Ediacaran fauna, 8effusive rock, formation, 12Egyptian iconography, 75El Capitan (Yosemite National Park, United

States), 44electric current, 25element, chemical, 8, 16, 20emerald, color, 32Eocene Epoch, 10eolian process (erosion), 14erosion, 14, 46

rock formation: See sedimentary rocksoil formation, 57

erratics, glaciers, 47estuary, 49Ethiopia

Borena ethnic group, 27Dallol volcano, 18-19, 26-27volcanic cave house, 4-5

exfoliation, 24, 63exotic mineral, quartz color, 22

extended cave system, 50Externsteine rock formation (Germany), 58extinction: See mass extinctionextrusive rock (volcanic rock), 65

formation, 12, 42, 43rock cycle, 57

Ffault (rock fracture), 13feldspar, 17fissure, granite rock, 45flowering plant, Cretaceous Period, 10fluorite, 39

hardness, 24foliation, 72fool's gold: See pyritefossil

Cambrian explosion, 9dating, 53, 91formation, 53hominid, 11succession, 52, 53

fractional distillation, 89fracture, 13, 24, 63

temperature effects, 15Fugitive Slave Law, 84fusion (rock), 55

Ggabbro (rock), 64galena, structure, 21garnet, color, 33garnetiferous schist, 72-73gas: See petroleumgem (precious stone), 18-19, 32-33geode, 60, 61geologic process: See erosion; weathering

Grand Canyon, 52-53, 66car, elements, 78-79carbon, mineral structure, 21carbon-14 dating, 53, 91carbonate, 39Carboniferous Period, 9carbonization, 70cascades, 45cataclasite, formation, 54Cathedral Rocks (Yosemite National Park,

United States), 45cation, 28cave, 50-51

Australian Aborigine paintings, 59formation, 49Neversink Pit, 40-41

cementation (sedimentary rock), 49, 69Cenozoic Era, 10-11Central Rocky Mountains (United States),formation, 10chalcopyrite, 38chalk, 68chemical element, 8, 16, 20chemical weathering process, 15Chicxulub (Mexico), meteor impact, 10Chile, Torres del Paine National Park, 16-17citrine, 22clast, detrital rocks, 68clay

kaoline, 68lutite, 68structure, 36

cliff, formation, 49coal

deposits, 71, 77formation, 70-71mining, 76-77, 86-87

coastal drift, 4coastal plain, 49color

mineral, 22: See also streak colorrock, 63

column (cave structure), 50compaction (sedimentary rock), 49compound mineral, 20


geologic time scale, 8-11rock layers, 53

geology, branches, 16Germany, Externsteine rock formation, 58Giant's Causeway (Northern Ireland), 65glacial cirque, 47glaciation

Precambrian Period, 8Quaternary Period, 11

glacier, 44, 47, 56glass, atomic model, 29gneiss, 72

formation, 9, 55metamorphism, 73

goldgold rush, 84-85metals, 20mining, 80-81

Gondwana (continent), 9grain (rock), 63Grand Canyon (United States), 52-53, 66granite, 12, 17, 42, 44, 45, 64granodiorite, 64graphite

chemical crystallization, 21hardness, 21use, 19Yosemite National Park, 44-45

graywacke, 69Great Koh-I-Noor diamond, 34Great Star of Africa diamond, 35Greece, ancient, architecture in Petra, 75gypsum, 39

hardness, 24use, 19

HHadean Era, 8Half Dome (Yosemite National Park, United

States), 45halide, 39

halite: See salthardness (mineral)

diamond, 21graphite, 21Mohs scale, 21, 24quartzite, 73

hematite, 23hexagonal crystalline system, 30Himalayas (Asia), formation, 10Holocene Epoch, 11Hope Diamond, 35hopper (mining equipment), 85hornblende schist, 72hornito (salt formation), 26, 27human being, emergence, 11humus, 57hydraulic mining, 85hydrocarbon, 78hydrologic process, erosion, 14hydroxide, 38

Iidiochromatic mineral, 22igneous rock, 64-65

formation, 42-43rock cycle, 57

immigrant labor, gold mining, 84India, diamond history, 34, 35inselberg, 46internal geodynamics, 12intrusive rock (plutonic rock), 64

formation, 12, 42rock cycle, 57

ionic bond, 28iron, 79isomorphism, 21

Mmagma, rock formation, 42, 43

See also igneous rock; volcanic rockmagmatism, 12magnesite, structure, 21magnesium, 78, 79magnetite, 38malachite, 22, 39mammal, Cenozoic Era, 10-11mammoth, 11, 91marble, 73

colors, 63marcasite, chemical crystallization, 21mass extinction

Cretaceous Period, 10Permian Period, 9

Mauna Loa volcano (Hawaii, United States), 12-13

McLean, Evelyn Walsh, 35Mecca (Saudi Arabia), Black Stone of the

Ka'bah, 59mechanical weathering process, 15Mesozoic Era, 10metal

car parts, 78-79luster, 23native minerals, 21, 22

metamorphic rock, 12classification, 72rock cycle, 57

metamorphism, 12, 54-55meteor, Yucatán Peninsula, 10Mexico, Yucatán Peninsula meteor, 10mica, 17micaceous schist, 72mineral, 18-39

chemical perspective, 17classification, 20-23optical property, 22-23physical properties, 24-25radioactive, 90-91sources, 5structure, 21

mineralization process, Dallol volcano, 26mining

coal, 76-77, 86-87copper, 82-83gold, 80-81, 84-85hydraulic, 85open-air mine, 82-83silver, 80-81types, 82

Miocene Epoch, 11Mohs, Friedrich, 24Mohs scale of hardness, 24-25

diamonds, 21graphite, 21

monoclinic crystalline system, 30monorefringent mineral, 23moraine, 47mother-of-pearl, 67mountain

formation, 9, 10, 11, 13See also specific names, for example Sierra

Nevada rangeMountain of Light (diamond): See Great

Koh-I-Noor diamondmylonite, formation, 54

NNabataean people, Petra, 74-75native mineral, 20Neversink Pit (Alabama, United States), 40-41nonmetal mineral, 20, 38

car parts, 79luster, 23

nonsilicate mineral, 38-39Northern Ireland, Giant's Causeway, 65nuclear energy, 77, 90-91nuclear reactor, 90-91

Oobsidian, 43, 65ocean

first, 8marine sediments, 66-67

Oligocene Epoch, 11olivine, 36opal, 32open-air mine, 82-83optical property (mineral), 22-23Ordovician Period, 9organic rock, 61, 70original horizontality principle, 53orogeny, 9orthoclase, hardness, 25oxide, 38

P-QPaleocene Epoch, 10Paleozoic Era, 9

calcareous formations, 66Pangea (continent), 9Panotia (supercontinent), 9Patagonia, formation, 11pearl, formation, 67peat bog, coal formation, 70pegmatite, 65peridotite, 64permafrost, 56Permian Period, 9Petra (Jordan), 74-75petrographic microscope, 22petroleum (gas)

combustion, 78formation and reserves, 70-71production process, 88-89

phosphate, 38phraetic layer, mining, 83phyllite, formation, 54, 72

J-Kjoint (rock fracture), 13Jordan, Petra, 74-75Jurassic Period, 10kaoline, 68

See also claykaolinite, 36karst cycle, 50Kilauea Crater (Hawaii, United States), 12-13Kimberley mine, 32Koh-I-Noor diamond, Great, 34

Llabradorite, 31laccolith, 43laterite soil, 56lava, 43leaching (lixiviation), 82lignite, 71limestone, 68

Externsteine formation, 58formation, 66karst cycle, 50Neversink Pit, 40-41stalactite formation, 51

limolite: See limestonelimonite, 38lithosphere, 11lixiviation (leaching), 82luminescence, 23luster, 23

pearl, 67lutite, 68


piezoelectricity, 25Pleistocene Epoch, 11Pliocene Epoch, 11plutonic rock (intrusive rock), 64

formation, 12, 42rock cycle, 57

polymorphism, 21porphyritic rock, 65positron emission tomography, 91Precambrian Period, 8precious stone, colors, 32-33

See also specific types, for example diamondpressure, effect on rock structure, 55prism, 30

Giant's Causeway, 65Proterozoic Era, 8pumice, 65pyrite (fool's gold)

chemical crystallization, 21structure, 39

pyroclastic material: See volcanic ashpyroelectricity, 25Quaternary Period, 11quartz

agate, 23color, 22composition, 17hardness, 25structure, 37

quartzite, 73

Rradioactive mineral, 90-91ranker (soil type), 56rapids, 48refining, petroleum, 89refraction, 23regional metamorphism, 55

See also metamorphism

reptileCretaceous Period extinction, 10Mesozoic Era, 10

rhodochrosite, 31rhombic crystalline system, 31river, sediment transportation, 48-49rock, 60-75

color, 62formation, 16-17, 62identification, 62-63mineralogical composition, 62shape, 62transformation: See metamorphismSee also specific types, for example granite

rock crystal, 22rock cycle, 6-7, 57Rocky Mountains (North America),

formation, 10Rodinia (early supercontinent), 8rose quartz, 22ruby, color, 32

Ssafety measure, radioactive material, 90, 91salt (halite), 19, 20

extraction, 27ionic bond, 28structure, 21, 28-29

salt deposit, hornito formation, 27sandstone

classification, 69Petra, 74-75Uluru, 58-59

sapphire, color, 33Saudi Arabia, Black Stone of the Ka'bah, 59scheelite, 31schist, 55

types, 72-73Scotland, gneiss formation, 9, 54-55sediment

soil formation, 56

stripe (rock), 72subsoil, 57sulfate, 39sulfide, 39sulfur, 19, 20, 22supercontinent, 8, 9

Ttalc, 37

hardness, 24Taylor, Elizabeth, 35Taylor-Burton diamond, 35temperature, degree of metamorphism, 55terminal moraine, 47Tertiary Period, 10-11tetragonal crystalline system, 31texture (rock), 63thyroid, scintillography, 91till, glaciers, 47topaz, 31

color, 33hardness, 25

Torres del Paine National Park (Chile), 16-17tourmaline, 24-25transportation, eroded materials, 15Triassic Period, 10triclinic crystalline system, 31trigonal crystalline system, 31trilobite, 9, 52tropics, laterite soil, 56tuff, detrital rocks, 68tunnel, formation, 51turquoise, color, 33

UUluru-Kata Tjuta National Park (Australia),

58-59unconformity, rock layers, 53United Kingdom

Giant's Causeway, 65royal family's diamond ownership, 34, 35

United States of AmericaBingham Canyon, 82-83Corkscrew Canyon, 6-7, 14-15gold mining, 84-85Grand Canyon, 52-53, 66Mauna Loa volcano, 12-13Neversink Pit, 40-41Yosemite National Park, 44-45

Ural Mountains (Eurasia), formation, 9uranium, 77

handling, 90medical uses, 91

VValley of Diamonds (legend), 35vanadinite, 30Veladero mine (Argentina), 80-81Victoria, Queen, Great Koh-I-Noor diamond, 34volcanic ash, 68

ash cone, 43volcanic rock (extrusive rock), 65

formation, 12, 42, 43rock cycle, 57

volcanocaldera, 43Dallol, 18-19, 26-27Mauna Loa 12-13rock formation, 42, 65

Wwater

cave formation, 50-51erosion, 14hornitos, 26, 27sediment transportation, 48-49weathering, 15

waterfallformation, 48Yosemite National Park, 45

weathering, 14, 15wind

deserts, 46erosion, 14sediment transportation, 47

Winston, Harry, 35

X-ZX-ray diffraction, 22

crystal structure identification, 28Yosemite National Park (United States), 44-45Yucatán Peninsula (Mexico), meteor, 10zooxanthellae, coral reefs, 67

fdf dsdfsdaf

water transportation, 48-49wind transportation, 47

sedimentary rockdetrital rock, 68-69formation, 46-49, 57marine organic remains, 66-67See also stalactite; stalagmite

sedimentation, 15, 48semimetal mineral, 20semiprecious stone

color, 33See also precious stone

Serapis (Egyptian god), 75Siberia, Ural Mountains formation, 9siderite, structure, 21Sierra Nevada range (United States), 44-45silicate, structures, 29, 36-37silicon, 79sill (rock formation), 42, 65Silurian Period, 9silver

crystal dendrite, 20mining, 80-81

sinkhole, 50slate, 39, 72

formation, 9micrography, 72phyllite formation, 54, 72

sluice box, 85Smithsonian Institution, Hope Diamond, 35smoky quartz, 22soil

formation, 56humus, 57profile, 57types, 56

South AfricaCango Caves, 50-51diamonds, 35

stalactite, 50formation, 51

stalagmite, 50stock (rock formation), 43streak color, 23

See also color

Rocks and Minerals

Education

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