Post on 04-Jun-2020
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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