Earth Science Unit 1.3Earth Science Unit 1.3Rocks & MineralsRocks & Minerals

ELEMENTSELEMENTS• EIGHT ELEMENTS MAKE UP MOST OF

ALL MINERALS ON THE EARTH– Elements combine to form Minerals

• LISTED IN ORDER OF ABUNDANCE– OXYGEN (O)– SILICON (Si)– ALUMINIUM (Al)– IRON (Fe)– CALCIUM (Ca)– POTASSIUM (K)– SODIUM (Na)– MAGNESIUM (Mg)

PERIODIC TABLE OF ELEMENTSPERIODIC TABLE OF ELEMENTS

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

– SILICATES – CONTAIN SILICON & OXYGEN MOLECULES (SiO)

– NON-SILICATES (NO SiO)

NON-SILICATE MINERALSNON-SILICATE MINERALS

• Make up 5% of Earth’s crust

• Native metals: gold, silver, copper

• Carbonates: calcite (used in cement)

• Oxides: hematite (iron ores)

• Sulfides: galena (lead ores)

• Sulfates: gypsum (used in plaster)

SILICATE MINERALSSILICATE MINERALS

• Make up 90-95% of the Earth’s Crust

• Dominant component of most rocks, include:– QUARTZ (SiO2)

– FELDSPARS

– MICAS

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:

– TEXTURE: • Size, shape and manner of growth of

individual crystals

– MINERAL COMPOSITION• Based on SiO content

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 ROCKSCLASSIFYING SEDIMENTARY ROCKSTHREE 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

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 water converts 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

Time for a break…Time for a break…

GEOLOGIC TIME AND DATINGGEOLOGIC TIME AND DATING

• Four basic principles– Principle of Original Horizontality

– Beds of sediment deposited in water formed as horizontal or nearly horizontal layers.

– Principle of Superposition– Within a sequence of undisturbed sedimentary or volcanic

rocks, the layers get younger going from bottom to top.

– Lateral Continuity– An original sedimentary layer extends laterally until it tapers or

thins at its edges

– Cross-cutting Relationships– A disrupted pattern is older than the cause of the disruption.

DATING - RELATIVEDATING - RELATIVE• Physical Continuity

– Physically tracing the course of a rock unit to correlate rocks between two different places

• Similarity of Rock Types– Correlation of two regions by assumption that similar rock types in two regions

formed at same time, under same circumstances

• Correlation by Fossils– Plants and animals that lived at the time rock formed were buried by

sediment

– fossil remains preserved in the layers of sedimentary rock -fossils nearer the bottom (in older rock) are more unlike -those near the top

– Observations formalized into Principle of Faunal Succession – fossil

species succeed one another in a definite and recognizable order.

– Index Fossil – a fossil from a short-lived, geographically widespread species known to exist during a specific period of geologic time.

ABSOLUTE DATING - ABSOLUTE DATING - DENDROCHRONOLGYDENDROCHRONOLGY

• Using annual growth rings of trees

• Dates for trees now extending back more than 9,000 years.

• Bristlecone Pine, White Mountains, CA (pinus longaeva) provides a continuous time scale for last 9,000 years (to 7000 B.C)

• Provides calibration of radiocarbon dates over most of the last 10,000 years (Holocene epoch)

DENDROCHRONOLOGYDENDROCHRONOLOGY

ABSOLUTE DATINGABSOLUTE DATINGVARVE CHRONOLOGYVARVE CHRONOLOGY

• Varves are parallel strata deposited in deep ocean floors or lake floors

• A pair of sedimentary layers are deposited during seasonal cycle of a single year– Laminae (similar to annual growth rings in trees)

record climatic conditions in a lake or large water body from year to year

• Cores extracted from sea floor or lake floor are used to date back several million years to 200 million years

VARVE CHRONOLOGYVARVE CHRONOLOGY

DATING - ABSOLUTEDATING - ABSOLUTE

• Radiometric dating – based on radioactive decay of ‘isotopes’

• Decay rate can be quantified because it occurs at a constant rate for each known isotope – “half-life” from parent isotope to stable ‘daughter’ isotope

• Measuring ratio of parent to daughter isotopes determines absolute ages of some rocks.

ABSOLUTE DATING ISOTOPESABSOLUTE DATING ISOTOPES• URANIUM–LEAD (U238–Pb206)

– Half-life: 4.5 billion years

– Dating range: 10 million – 4.6 billion years

• URANIUM–LEAD (U235-Pb207)– Half-life: 713 million years

– Dating Range: 10 million – 4.6 billion years

• POTASSIUM-ARGON (K40-Ar40)– Half-life: 1.3 billion years

– Dating Range: 100,000 – 4.6 billion years

• CARBON-14 (C14-N14)– Half-life: 5730 years

– Dating Range: 100 – 100,000 years