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MINERALS AND ROCKS MINERALS AND ROCKS IN THE EARTHIN THE EARTH’’S CRUSTS CRUSTIgneous, Sedimentary, Metamorphic Rocks Igneous, Sedimentary, Metamorphic Rocks
and Environmentsand Environments
ELEMENTSELEMENTS
• Chemical elements are the fundamental materials of which all matter is composed.– From the modern viewpoint:
• a substance that cannot be broken down or reduced further
ELEMENTSELEMENTS• ALMOST ALL THE MINERALS FOUND IN THE
EARTH ARE FORMED FROM THE BONDING OF 8 ELEMENTS
• LISTED IN ORDER OF ABUNDANCE– OXYGEN (O)– SILICON (Si)– ALUMINIUM (Al)– IRON (Fe)– CALCIUM (Ca)– POTASSIUM (K)– SODIUM (Na)– MAGNESIUM (Mg)
MINERALSMINERALS
• BUILDING BLOCKS FOR ROCKS• DEFINITION:
– NATURALLY OCCURRING, – INORGANIC SOLIDS, – CONSISTING OF SPECIFIC CHEMICAL
ELEMENTS, AND – A DEFINITE ATOMIC ARRAY
• CRYSTALLINE STRUCTURE – ‘CRYSTAL’
MINERALSMINERALS
• MINERALS: • TWO CATEGORIES BASED ON SILICA
CONTENT (SiO – silicon-oxygen molecule)– SILICATES – CONTAIN SILICON - OXYGEN
MOLECULE (SiO)– NON-SILICATES (NO SiO)
NONNON--SILICATE MINERALSSILICATE MINERALS
• Non-silicate minerals are very rare• Make up 5% of Earth’s continental crust
– Considered valuable commercially as building materials, gemstones, iron ores for steel, ceramics, and more.
• Native metals: gold, silver, copper• Carbonates: calcite (used in cement)• Oxides: hematite (iron ores)• Sulfides: galena (lead ores)• Sulfates: gypsum (used in plaster, dry wall)
SILICATE MINERALSSILICATE MINERALS
• THE MOST ABUNDANT OF ALL MINERALS– MAKE UP 90-95% OF WEIGHT OF EARTH’S
CRUST– CONTAIN VARYING AMOUNTS OF SILICA (SiO)
• DOMINANT COMPONENT OF MOST ROCKS: – IGNEOUS– SEDIMENTARY – METAMORPHIC
SILICATE MINERALS SILICATE MINERALS • LISTED BELOW IN DECREASING % OF SILICA ARE
MOST COMMON SILICATE MINERALS
• QUARTZ (SiO2) (“High” Silica content ~100%)
• FELDSPARS (PLAGIOCLASE - (Na,Ca)(Si,Al)4O8 )
• MICAS (MUSCOVITE -KAl2(AlSi3O10)(F, OH)2 and BIOTITE - K (Fe, Mg)3 AlSi3 O10 (F, OH)2 )
• AMPHIBOLES (Hornblende -Ca2(Fe,Mg)5Si8O22(OH2)
• PYROXENES (Augite – {Mg,Fe}SiO3)• OLIVINE - (Mg, Fe)2SiO4, (“Low” Silica content ~40%)
FELSIC SILICATE MINERALS FELSIC SILICATE MINERALS
• MINERALS WITH HIGH CONCENTRATION OF SILICON, OXYGEN, ALUMINIUM AND POTASSIUM
• FELSIC SILICATES – HIGH % SiO– QUARTZ (100% SiO2)– FELDSPARS (Plagioclase, Orthoclase)– MUSCOVITE MICA
MAFIC SILICATE MINERALSMAFIC SILICATE MINERALS
• MINERALS WITH HIGH CONCENTRATION OF MAGNESIUM AND IRON, PLUS CALCIUM AND SODIUM, AND LOWER AMOUNTS OF SILICON AND OXYGEN
• MAFIC SILICATES - LESS SiO– BIOTITE MICA– AMPHIBOLE (Hornblende)– PYROXENE (Pyroxene)
ULTRAMAFIC SILICATESULTRAMAFIC SILICATES• MINERALS WITH GREATER
CONCENTRATION IN MAGNESIUM AND IRON. VERY RARE AT EARTH’S SURFACE
• ULTRA MAFIC SILICATES - VERY LOW % SiO
• VERY RARE AT SURFACE– OLIVINE
ROCKSROCKS
• AGGREGATIONS OF 2 OR MORE MINERALS– Same or different minerals combine together
• THREE CATEGORIES– IGNEOUS– SEDIMENTARY– METAMORPHIC
IGNEOUS ROCKSIGNEOUS ROCKS
• FORMED FROM COOLED, SOLIDIFIED MOLTEN MATERIAL AT, OR BELOW, THE SURFACE
• PLUTONIC (INTRUSIVE) - COOLED BELOW SURFACE AT GREAT DEPTHS
• VOLCANIC (EXTRUSIVE) - COOLED AT OR NEAR THE SURFACE THROUGH VOLCANIC ERUPTIONS
IDENTIFICATION OF IGNEOUS IDENTIFICATION OF IGNEOUS ROCKSROCKS
• IDENTIFICATION PROCESSES FOR PLUTONIC OR VOLCANIC IGNEOUS ROCKS:– TEXTURE:
• Size, shape and manner of growth of individual crystals
– MINERAL COMPOSITION• Based on SiO content
– Felsic, Intermediate, Mafic
TEXTURE IDENTIFICATIONTEXTURE IDENTIFICATION• SIZE, SHAPE OF CRYSTALS AND MANNER
OF GROWTH• APHANITIC TEXTURE:
– FINE-GRAINED – VERY TINY, MINERAL CRYSTALS VISIBLE ONLY WITH MAGNIFICATION
– INDICATES FAST COOLING AT SURFACE
• PHANERITIC TEXTURE: – COARSE-GRAINED – LARGE, EASILY-VISIBLE
MINERAL CRYSTALS– INDICATES SLOW COOLING AT DEPTH
MINERAL COMPOSITIONMINERAL COMPOSITION
• CLASSIFIED BY SILICA (SiO) CONTENT
• FELSIC – MORE THAN 85% SILICA
• INTERMEDIATE – 60-85% SILICA
• MAFIC – LESS THAN 60% SILICA
COMMON IGNEOUS ROCKSCOMMON IGNEOUS ROCKS• GRANITE: PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE; FELSIC
MINERAL COMPOSITION
• RHYOLITE: VOLCANIC-EXTRUSIVE; APHANETIC TEXTURE; FELSIC MINERAL COMPOSITION
• DIORITE: PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE; INTERMEDIATE MINERAL COMPOSITION
• ANDESITE: VOLCANIC-EXTRUSIVE; APHANETIC TEXTURE; INTERMEDIATE MINERAL COMPOSITION
• GABBRO: PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE; MAFIC MINERAL COMPSITION
• BASALT: VOLCANIC-EXTRUSIVE; APHANETIC TEXTURE; MAFIC MINERAL COMPOSITION
OTHER IGNEOUS ROCKSOTHER IGNEOUS ROCKS• VOLCANIC GLASS:
– OBSIDIAN: VOLCANIC-EXTRUSIVE; NO CRYSTALS FORM; SILICA-RICH, COOLED INSTANEOUSLY
– PUMICE: VOLCANIC-EXTRUSIVE; NO CRYSTALS FORM; SILICA-RICH; SOLIDIFIED FROM ‘GASSY’ LAVA
• PYROCLASTIC ROCKS– TUFF: VOLCANIC-EXTRUSIVE;
SOLIDIFIED ‘WELDED’ ASH
SEDIMENTARY ROCKSSEDIMENTARY ROCKS
• WEATHERING PROCESSES BREAK ROCK INTO PIECES, SEDIMENT, READY FOR TRANSPORTATION DEPOSITION BURIAL LITHIFICATION INTO NEW ROCKS.
CLASSIFYING SEDIMENTARY CLASSIFYING SEDIMENTARY ROCKSROCKS
• THREE SOURCES• Detrital (or clastic) sediment is composed of
transported solid fragments (or detritus) of pre-existing igneous, sedimentary or metamorphic rocks
• Chemical sediment forms from previously dissolved minerals that either precipitated from solution in water , or were extracted from water by living organisms
• Organic sedimentary rock consisting mainly of plant remains
CLASTIC SEDIMENTARY ROCKSCLASTIC SEDIMENTARY ROCKS• CLASSIFIED ON GRAIN OR PARTICLE
SIZE• Shales: finest-grained• Sandstones: medium-grained• Conglomerates – Breccias: coarse-grained
SHALESSHALES
• SHALES: finest-grained – composed of very small particles (from <0.004-0.063 mm)– 50% of all sedimentary rocks are Shales– Consist largely of Clay minerals – Subcategories: Claystones; Siltstones;
Mudstones– Economic value: building material; china
and ceramics; spark plug housings
SANDSTONESSANDSTONES• SANDSTONES: medium-grained; particle-
size (0.063-2 mm)• 25% of all sedimentary rocks fall into this
category • Economic value: glass; natural reservoirs
for oil, gas, and groundwater
CONGLOMERATES CONGLOMERATES -- BRECCIASBRECCIAS
• CONGLOMERATES AND BRECCIAS:• The coarsest of all the detrital sedimentary
rocks • Composed of particles >2 mm in diameter
– Conglomerate - the particles are rounded – Breccia - the particles are angular
CHEMICAL SEDIMENTARY CHEMICAL SEDIMENTARY ROCKSROCKS
• TWO CATEGORIES:
– INORGANIC CHEMICAL SEDIMENTARY
– ORGANIC CHEMICAL SEDIMENTARY
INORGANIC CHEMICAL INORGANIC CHEMICAL SEDIMENTARY ROCKSSEDIMENTARY ROCKS
• Formed when dissolved products of chemical weathering precipitate from solution
• Most common types:– Inorganic limestones and cherts: precipitates
directly from seawater and fresh water– Evaporites: precipitates when ion-rich water
evaporates – Dolostones: Origin is still in debate
INORGANIC INORGANIC -- LIMESTONESLIMESTONES
• Limestones - account for 10% - 15% of all sedimentary rocks formed from Calcite or Calcium Carbonate (CaCO3).
• Formed as pure carbonate muds accumulate on the sea floor
• Also formed on land:– Tufa - a soft spongy inorganic limestone that forms where underground
water surfaces
– Travertine - forms in caves when droplets of carbonate-rich water on the ceiling, walls and floors precipitate a carbonate rock
ORGANIC LIMESTONESORGANIC LIMESTONES• Formed with calcite from marine environment: CaCO3
shells and internal/external skeletons of marine animals
• Coquina - “crushed” shell fragments cemented with CaCO3• Chalk - made from billions of microscopic carbonate-secreting
organisms • Coral Reefs - Formed from the skeletons of millions of tiny
invertebrate animals who secrete a calcite-rich material. Live “condo” style while algae acts as the cement to create the large structures called “reefs”.
• Organic Chert - formed when silica-secreting microscopic marine• organisms die (radiolaria {single-celled animals} and
diatoms {skeletons of singled-celled plants})• Flint - an example of an Organic Chert
ORGANIC SEDIMENTARY ORGANIC SEDIMENTARY ROCKSROCKS
• Coal - Organic sedimentary rock consisting mainly of plant remains • Formation:
– Burial of decaying vegetation;
– Increasing pressure from the overlying layers expels water, CO2 and other gases;
– Carbon accumulates.• STAGES:• Peat - formed early in the process, when the original plant structure• can still be distinguished. • Lignite - a more hardened form of Peat• Bituminous - more pressure and more heat produce this moderately• hard coal. • Anthracite - the hardest coal - formed from metamorphic processes• under extreme heat and pressure - Hard - Shiny - the most• desired as an energy resource.
SEDIMENTARY ENVIRONMENTSSEDIMENTARY ENVIRONMENTS
• Lakes• Lagoons• Rivers• Ocean bottoms
• Estuaries• Salt Flats• Playas• Glacial environments
SEDIMENTARY PROCESSESSEDIMENTARY PROCESSES
• LITHIFICATION:• As sediment is buried several kilometers beneath the surface, heated from
below, pressure from overlying layers and chemically-active waterconverts the loose sediment into solid sedimentary rock
• Compaction - volume of a sediment is reduced by application of pressure
• Cementation - sediment grains are bound to each other by materials originally dissolved during chemical weathering of preexisting rocks – typical chemicals include silica and calcium carbonate.
METAMORPHIC ROCKSMETAMORPHIC ROCKS
• METAMORPHISM : process by which conditions within the Earth alter the mineral content and structure of any rock, igneous, sedimentary or metamorphic, without melting it.
• Metamorphism occurs when heat and pressure exceed certain levels, destabilizing the minerals in rocks...but not enough to cause melting
• Ion-rich fluids circulating in and around rocks also influences metamorphism
METAMORPHIC PROCESSESMETAMORPHIC PROCESSES• HEAT: Temperatures needed to
metamorphose rock (2000 C or 4000 F) reached near 10 km (6 miles) beneath the surface.
• PRESSURE: Requires pressure > 1 bar or 1000 mb, which is generally found ~ 3 km (2 miles) beneath the Earth’s surface
• FLUIDS: Water is the usual fluid and comes from various sources
• TEMPERATURE/PRESSURE – For every 3 kilometers depth in
the Earth, pressure increases by about 1 kb.
– Average temperature gradient in the Earth increases 30° C per km
CHANGES IN METAMORPHIC CHANGES IN METAMORPHIC ROCKSROCKS
• Metamorphic processes cause many changes in rocks – increased density– growth of larger crystals– reorientation of the mineral grains into layers
or banded texture • FOLIATION
– transformation of low-temperature minerals into high-temperature minerals
CLASSIFYING METAMORPHIC CLASSIFYING METAMORPHIC ROCKSROCKS
• TEXTURE: the size, shape and distribution of particles in a rock– texture is determined by grade of
metamorphism • Low grade: (less than 6000C and 4 kilobars pressure)
• Intermediate grade: occurs at a variety of temperatures and pressures.
• High grade: (greater than 6000C and 4 kilobars pressure)
FOLIATED TEXTURESFOLIATED TEXTURES
• Foliated texture: more pressure and mineral grains realign themselves and grow into larger crystals
• Three types of foliated texture: – Rock or Slaty Texture– Schistosity– Gneissic Texture
ROCK ROCK –– SLATY TEXTURE SLATY TEXTURE --SLATESLATE
• Shale metamorphosed to Slate: – clay minerals (stable at surface temperatures
and pressures) become unstable and recrystallize into mica crystals
– Slate is formed under Low-Grade Metamorphism
SCHISTOCITY SCHISTOCITY -- SCHISTSCHIST• More extreme pressures and temperatures: mica
crystals grow even larger - ~ 1 cm in diameter. – rock has “scaly” appearance - schistosity, – referred to as a Schist.
• Schists formed under Intermediate-Grade Metamorphism
• Schists named for the mineral constituents in the parent rock: – mica schist– talc schist– garnet schist
GNEISSIC TEXTURE GNEISSIC TEXTURE -- GNEISSGNEISS
• Light and dark silicate minerals separate and re-align themselves into bands
• Rocks with this texture are called Gneiss• Gneiss forms from High Grade Metamorphism• Typical ‘parent’ rocks for Gneiss
– granite – diorite– gabbro– shale.
NONNON--FOLIATED TEXTURESFOLIATED TEXTURES
• Rocks with only one mineral metamorphose without a visibly foliated texture
• Limestone metamorphoses into Marbleas the interlocking calcite crystals grow larger
• Quartz Sandstone metamorphoses into Quartzite
METAMORPHIC ENVIRONMENTSMETAMORPHIC ENVIRONMENTS• CONTACT METAMORPHISM
– Metamorphism of a rock touched by the intense heat of migrating magma.
• REGIONAL METAMORPHISM– Burial metamorphism - occurs when rocks are overlain by more than 6
miles of rock or sediment– Dynamothermal metamorphism - occurs when rocks are caught
between two convergent plates during mountain building • OTHER METAMORPHIC ENVIRONMENTS
– Hydrothermal metamorphism - chemical alteration of preexisting rocks by hot seawater near seafloor spreading or subduction zones
– Fault metamorphism - occurs as rocks grinding past one another create a form of directed pressure, as well as considerable frictional heat
– Shock metamorphism - occurs when a meterorite strikes the Earth surface, resulting in tremendous pressures and temperatures at the impact sites. The “shocked” minerals do not fracture, but rather recrystallize