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RocksReading this week: Ch. 2 and App. C

Reading for next week: Ch. 3

I. Environmental significanceII. DefinitionIII. 3 major classesIV. The Rock CycleV. Secondary classificationVI. Additional sub-classesVII. Important rock properties

RocksEnvironmental Significance

sheltertools

foundations

construction materials hazards

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RocksDefinition of a rock

• Naturally occurring• Solid• Cohesive aggregate of one or more– minerals or– mineral materials*

* mineral materials include non-crystalline solids

Amber OpalVolcanic glass

RocksDefinition of a rock

• Naturally occurring• Solid• Cohesive aggregate of one or more– minerals or– mineral materials*– plus/minus organic compounds

Tar Bitumen

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Rocks3 Major Classes

Based on processes of formation

Cooling of Magma (molten igneous rock)

Igneous

Lithification (turning to rock)of sediments

Sedimentary

Recrystallization under pressure and/or heat

Metamorphic

RocksThe Rock Cycle

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RocksSecondary Classification

Processes of formation - IgneousCooling of

magma at depth

Plutonic(from Pluto, god of

the underworld)e.g. granite

Cooling of lava (magma that erupts) at the surface

Volcanic(from a volcano)

e.g. basalt

Fusing of rock fragments and ash

erupted from volcano

Pyroclastic(pyr = fire,

clast = fragment)e.g. tuff

RocksSecondary Classification

Processes of formation - SedimentaryCompaction and

cementation of clasts(lithification)

Clastic sedimentary rockse.g. sandstone

Biotic or abiotic precipitation of minerals from water

Coquina limestone EvaporiteChemical sedimentary rocks

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RocksSecondary Classification

Processes of formation - MetamorphicHeat from a local, adjacent source

Contact metamorphism(reddish zone around granite)

Heat and pressure at depth in the crust

Regional metamorphism(entire subducting plate)

RocksAdditional Classification - Igneous

Texture - reflects cooling rateSlow Fast

Mixed rates

tuffporphyry

pegmatite obsidian

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Major Mineral GroupsSilicates (all with Si and O)

Aluminosilicates(felsic minerals)

• Al + Ca, Na, K• Example: feldspar

Ferromagnesian silicates(mafic minerals)

• Fe, Mg• Example: olivine

Major minerals (with quartz) of continental crust

Major minerals of oceanic crust

RocksAdditional Classification - Igneous

Mineralogic composition

Felsic Mafic

Rhyolite BasaltAndesite

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RocksAdditional Classification -

Clastic Sedimentary RocksGrain size

SandstoneConglomerate Shale

Coarse Fine

Major Mineral GroupsNonsilicates

• Carbonates, CO3(limestone)

• Halides (evaporites)Cl, F, or I salts

• Native Elements• Sulfides, S + metal• Sulfates, SO4• Oxides, O + metal• Hydroxides, OH +

metal

• Calcite, dolomite

• Halite, fluorite, silvite

• Gold, copper, graphite• Pyrite, galena• Gypsum• Magnetite, hematite• Gibbsite (Al), goethite (Fe)

Rockforming minerals

Accessory minerals

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RocksAdditional Classification -

Chemical SedimentsCalcite [CaCO3] or

Dolomite [CaMg(CO3)2]

Carbonates (Limestone, Dolomite)

Sulfates (gypsum) and Halides (halite,silvite)

Evaporites

RocksAdditional Classification - Metamorphic

Texture - reflects “metamorphic grade”Low

Slate

Medium

Schist

High

Gneiss

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RocksAdditional Classification - Metamorphic

Mineralogic composition - reflects “parent” rock

Quartzite

Sandstone Limestone

Marble

Shale

Slate

RocksImportant Properties

Mechanical Properties: response to stress

Folding of rocks occurs when they behave “plastically”

Faulting (rupture of brittle rocks)

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RocksImportant Properties (continued)

Resistance to physical weathering

Columnar basalt breaks along cracks that developed when lava cooled

Weakly cemented sandstone is easily eroded by waves

RocksImportant Properties (continued)

Resistance to chemical weathering by exposure to water

Cave formation resulting from carbonate dissolution

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RocksImportant Properties (continued)

Capacity to store and transmit fluids (water, oil, gas) depends on size and abundance of pores (open spaces)

Micropores in sandstones and carbonates Virtually no pores in granite

Macropores in limestone, basalt, crystalline rocks