Chapter 2bMineral and RocksMinerals• A mineral is a naturally occurring,homogeneous solid of definite chemicalcomposition and ordered atomic arrangementthat is usually formed by inorganic processes.• A Natural Crystalline PhaseMinerals• A mineral must occur naturally.• It must be chemically homogeneous down to theatomic level• It must have a chemical formula (eg SiO2, FeS2)• It must have a defined crystal structure.• It must be inorganic (not the result of biologicalprocesses alone).Some Familiar Minerals• Quartz (SiO2)• Pyrite (FeS2)• Calcite (CaCO3)• Gold (Au)• Silver (Ag)• Copper (Cu)• Diamond (C)• Graphite (C)• K-feldspar (KAlSi3O8)• Na-feldspar (NaAlSi3O8)• Olivine (Mg2SiO4)• Garnet (Mg3Al2Si3O12)• Gypsum (CaSO4H2H2O)• Apatite (Ca5 ( PO4) 3OH)•Ice (H2O)Some Non-Mineral Solids• Obsidian (Glass)• Opal (Amorphous)• Coal (Amorphous)• Wood (Organic)• Amber (Organic)Polymorphs• Same composition - different structure– Graphite - Diamond (C)– Quartz - Tridymite - Cristobalite - Coesite– Calcite - Aragonite (CaCO3)– Pyrite - Marcasite (FeS2)Isomorphs• Same Structure - Different Composition– Olivine (Mg2SiO4) (Fe2SiO4)– Calcite - Rhodochrosite (CaCO3) (MnCO3)– Apatite (Ca5 ( PO4) 3OH) - (Ca5 ( PO4) 3F)Mineral Properties• Hardness (Mohs Scale)•Luster•Color• ShapeA Rock is an Aggregate of Minerals• Igneous -– Crystallized from melts– Surface - Volcanic; Subsurface - Intrusive• Sedimentary -– Deposited from air and water on the surface• Metamorphic– Recrystallized from pre-existing igneous orsedimentary
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