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 VII. Important rock properties Environmental Significance 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 Volcanic glass Amber Opal Definition of a rock Naturally occurring Solid Cohesive aggregate of one or more minerals or mineral materials* plus/minus organic compounds Tar Bitumen
3 Major Classes Based on processes of formation Cooling of Magma Lithification (turning to rock) (molten igneous rock) of sediments Recrystallization under pressure and/or heat Igneous Sedimentary Metamorphic The Rock Cycle
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 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 Secondary Classification Processes of formation - Sedimentary Compaction and cementation of clasts (lithification) Biotic or abiotic precipitation of minerals from water Clastic sedimentary rocks e.g. sandstone Coquina limestone Evaporite Chemical sedimentary rocks
Secondary Classification Processes of formation - Metamorphic Heat from a local, adjacent source Heat and pressure at depth in the crust Contact metamorphism (reddish zone around granite) Regional metamorphism (entire subducting plate) Additional Classification - Igneous Texture - reflects cooling rate Slow Fast pegmatite Mixed rates obsidian porphyry tuff
Major Mineral Groups Silicates (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 Additional Classification - Igneous Mineralogic composition Rhyolite Andesite Basalt Felsic Mafic
Additional Classification - Clastic Sedimentary Grain size Conglomerate Sandstone Shale Coarse 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) Carbonates (Limestone, Dolomite) Evaporites Additional Classification - Metamorphic Texture - reflects metamorphic grade Low Medium High Slate Schist Gneiss
Additional Classification - Metamorphic Mineralogic composition - reflects parent rock Sandstone Limestone Shale Quartzite Marble Slate Mechanical Properties: response to stress Important Properties Folding of rocks occurs when they behave plastically Faulting (rupture of brittle rocks)
Important Properties (continued) Resistance to physical weathering Columnar basalt breaks along cracks that developed when lava cooled Weakly cemented sandstone is easily eroded by waves Important Properties (continued) Resistance to chemical weathering by exposure to water Cave formation resulting from carbonate dissolution
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