Geology 101 1st Edition Lecture 7 Outline of Last Lecture Measuring Plate Motion What Drives Plate Motions Importance of Plate Tectonics Animation of Hotspot and Volcanic Tracks Minerals Building Blocks Atoms Building Blocks of Minerals Chemical Bonds Isotopes and Radioactive Decay Formation of Minerals Outline of Current Lecture Structural Variations Physical Properties Mineral Classes Common Silicate Minerals Important Nonsilicate Minerals Magma Parent Material Of Igneous Rocks Igneous Processes Igneous Composition Current Lecture Structural Varation o Polymorphs Minerals with same composition but different crystalline structure Example o Diamond and Graphite carbon Covalent bonds in a 3D framework diamond Covalent bonds into sheets weak metallic between sheet graphite Phase change One polymorph changes into another one Different environments Physical Properties o Primary diagnostic properties Determined by observation or performing a simple test Luster o Appearance of a mineral in reflected light Metallic Nonmetallic Color Geology 101 1st Edition o Generally unreliable for identification o Often highly variable due to slight changes in mineral chemistry o Exotic colorations produce gemstones Streak o Color of mineral in its powdered form Hardness o Resistance of mineral to abrasion or scratching o All minerals are compared to a standard scale called the Mons Scale of Hardness Cleavage o Tendency to break along planes of weak bonding o Produces flat shiny surface Fracture o Absence of cleavage when a mineral is broken Specific Gravity o Weight of a mineral weight of an equal volume of water o Average value 2 7 Mineral Classes o Based on anions o Most abundant elements in crust Oxygen 47 Silicon 38 Other 6 o Silicates Most important mineral group Comprise most rock forming minerals Silicon oxygen tetrahedron Fundamental building block Four oxygen ions surrounding a much smaller silicon ion o Join silicate Structures Isolated tetrahedral Olivine Single and double chain Share Oxygen Sheet or layered structure Share 3 of the 4 Oxygen Muscovite 3 D structures Share all 4 Oxygen Common Silicate Minerals o Light silicates Lack iron magnesium Feldspar o Most common Quartz Geology 101 1st Edition o o Entirely oxygen and silicon Muscovite o Common member of Mica family Clay minerals o Originate from chemical weathering Dark silicates Contain iron magnesium Olivine o High temp Fe Mg silicates Pyroxene o Single chain structure Amphibole o Double chain structure Biotite o Iron rich member of the mica family o Sheet structure Garnet o Metamorphic Important Nonsilicate Minerals o Carbonates Primary constituents in limestone and dolostone Calcite CaCO3 and dolomite CaMgCO3 are two most important o Economic value Oxides Hematite o Magnetic for iron Halites Salt Sulfides Zinc ore Native copper Magma Parent Material of Igneous Rocks o Magma Melt below earth s surface Parent material of igneous rocks Forms from partial melting Normally contains volatiles H2O CO2 SO2 When cools it crystallizes and forms igneous rocks o Lava Melts at surface Igneous Processes o Intrusive Magma crystallizes at depth Black Hills o Extrusive Geology 101 1st Edition Lava solidifies at Earth s Surface Volcanic rocks Cascade Range Igneous Composition o Silicate minerals primarily o Dark silicates o Light silicates o Four compositional groups Silica SiO2 content for comparison o Two basic compositional groups Granite felsic Light colored High silica content Major constituent of continental crust Basaltic Dark Calcium rich Higher density Comprise of ocean floor and volcanic islands o Other 2 groups Intermediate Andesitic 25 of dark silicates Associated with explosive volcanic activity Ultramafic Rare at earth s surface Main constituent at mantle Composed entirely of ferromagnesian silicates