Rocks Environmental Significance. Rocks Reading this week: Ch. 2 and App. C Reading for next week: Ch. 3. Rocks Definition of a rock

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1 Reading this week: Ch. 2 and App. C Reading for next week: Ch. 3 Environmental Significance I. Environmental significance II. Definition III. 3 major classes IV. The Rock Cycle V. Secondary classification VI. Additional sub-classes VII. Important rock properties shelter tools foundations construction materials hazards Definition of a rock Naturally occurring Solid Cohesive aggregate of one or more minerals or mineral materials* * mineral materials include non-crystalline solids Definition of a rock Naturally occurring Solid Cohesive aggregate of one or more minerals or mineral materials* plus/minus organic compounds Tar Bitumen Volcanic glass Amber Opal

3 Major Classes Based on processes of formation The

to rock) (molten igneous rock) of sediments

Igneous Sedimentary Metamorphic Secondary

Cooling of magma at depth Cooling of lava (magma

fragments and ash erupted from volcano Secondary

minerals from water Plutonic (from Pluto, god of

granite Volcanic (from a volcano) e.g. basalt

2 3 Major Classes Based on processes of formation The Rock Cycle Cooling of Magma Lithification (turning to rock) (molten igneous rock) of sediments Recrystallization under pressure and/or heat Igneous Sedimentary Metamorphic Secondary Classification Processes of formation - Igneous Cooling of magma at depth Cooling of lava (magma that erupts) at the surface Fusing of rock fragments and ash erupted from volcano Secondary Classification Processes of formation - Sedimentary Compaction and cementation of clasts (lithification) Biotic or abiotic precipitation of minerals from water Plutonic (from Pluto, god of the underworld) e.g. granite Volcanic (from a volcano) e.g. basalt Pyroclastic (pyr = fire, clast = fragment) e.g. tuff Clastic sedimentary rocks e.g. sandstone Coquina limestone Evaporite Chemical sedimentary rocks

3 Secondary Classification Processes of formation - Metamorphic Heat from a local, adjacent source Heat and pressure at depth in the crust Additional Classification - Igneous Texture - reflects cooling rate Slow Fast pegmatite Mixed rates obsidian Contact metamorphism (reddish zone around granite) Regional metamorphism (entire subducting plate) porphyry tuff Major Mineral Groups Silicates (all with Si and O) Additional Classification - Igneous Aluminosilicates (felsic minerals) Al + Ca, Na, K Example: feldspar Ferromagnesian silicates (mafic minerals) Fe, Mg Example: olivine Mineralogic composition Rhyolite Andesite Basalt Major minerals (with quartz) of continental crust Major minerals of oceanic crust Felsic Mafic

Additional Classification - Clastic Sedimentary Grain

Elements Sulfides, S + metal Sulfates, SO 4 Oxides, O

Nonsilicates Rockforming minerals Carbonates, CO 3

Halite, fluorite, silvite Cl, F, or I salts Accessory

Magnetite, hematite Gibbsite (Al), goethite (Fe)

[CaCO 3 ] or Dolomite [CaMg(CO 3 ) 2 ] Sulfates

Classification - Metamorphic Texture - reflects

4 Additional Classification - Clastic Sedimentary Grain size Conglomerate Coarse Sandstone Shale Fine Native Elements Sulfides, S + metal Sulfates, SO 4 Oxides, O + metal Hydroxides, OH + metal Major Mineral Groups Nonsilicates Rockforming minerals Carbonates, CO 3 Calcite, dolomite (limestone) Halides (evaporites) Halite, fluorite, silvite Cl, F, or I salts Accessory minerals Gold, copper, graphite Pyrite, galena Gypsum Magnetite, hematite Gibbsite (Al), goethite (Fe) Additional Classification - Chemical Sediments Calcite [CaCO 3 ] or Dolomite [CaMg(CO 3 ) 2 ] Sulfates (gypsum) and Halides (halite,silvite) Additional Classification - Metamorphic Texture - reflects metamorphic grade Low Medium High Carbonates (Limestone, Dolomite) Evaporites Slate Schist Gneiss

5 Additional Classification - Metamorphic Mineralogic composition - reflects parent rock Sandstone Limestone Shale Mechanical Properties: response to stress Important Properties Folding of rocks occurs when they behave plastically Quartzite Marble Slate Faulting (rupture of brittle rocks) Important Properties (continued) Resistance to physical weathering Important Properties (continued) Resistance to chemical weathering by exposure to water Columnar basalt breaks along cracks that developed when lava cooled Weakly cemented sandstone is easily eroded by waves Cave formation resulting from carbonate dissolution

Important Properties (continued) Capacity

carbonates Virtually no pores in granite

6 Important 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

Rocks Reading this week: Ch. 2 and App. C Reading for next week: Ch. 3

Rocks Reading this week: Ch. 2 and App. C Reading for next week: Ch. 3 Reading this week: Ch. 2 and App. C Reading for next week: Ch. 3 I. Environmental significance II. Definition III. 3 major classes IV. The Rock Cycle V. Secondary classification VI. Additional sub-classes