minerals and rocks - west valley college
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Robert Lopez, West Valley Community College
Minerals and RocksOcean 10
Minerals• A mineral is (four-part definition):
– 1.– 2.– 3.– 4.
• Consistent and recognizable physicaland chemical properties
Silicate Structures
• The Silicon-Oxygen tetrahedron– (SiO4)-4
• Sharing of O atoms in tetrahedra orbalanced by cations
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Non-silicate Minerals• Carbonates
– (e.g., calcite - CaCO3)• Sulfates
– (e.g., gypsum - CaSO4. 2H2O)
• Sulfides– (e.g., pyrite - FeS2)
• Oxides– Contain O, not bonded to Si, C or S (e.g., hematite - Fe2O3)
• Native elements– (e.g., diamond - C; gold - Au)
Mineral Properties• Color
– Best for mafic vs. felsicminerals
• Streak– Color left behind when mineral
is scraped on unglazed porcelain• Luster
– Metallic or Non-metallic• Hardness
– Mohs hardness• Crystal form
– Characteristic Habit
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Crystal Habit
Mineral Properties
• Cleavage– Breakage along flat planes
• Fracture– Irregular breakage
• Specific gravity– Density relative to that of water
• Magnetism– Attracted to magnet
• Chemical reaction– Calcite fizzes in dilute HCl
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The Rock CycleA rock is composed of one or
more mineralsThe rock cycle shows
transformation in nature
Igneous Rocks
• Magma is• Igneous rocks share one common
characteristic _____________!!– Intrusive
• Granite is a common example– Extrusive (lava or tephra)
• Basalt/tuff is a common example
Granite
Basalt
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Igneous Rock Textures• Texture and Composition =• Texture controlled by cooling rate• Extrusive rocks cool quickly• Intrusive rocks cool slowly
Coarse-grained igneous rock, granite
Fine-grained igneous rock, tuff
Special Igneous Textures• Pegmatite Texture
• Glassy texture
• Porphyritic texturePegmatitic igneous rock
Porphyritic igneous rock
Igneous Rock Chemistry• Rock chemistry, particularly silica (SiO2) content,
determines mineral content and general color of igneousrocks
– Mafic rocks– Intermediate rocks– Felsic (silicic) rocks– Ultramafic rocks
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Igneous Activity andPlate Tectonics
• Mafic igneous rocks arecommonly formed atdivergent boundaries
• Intermediate igneousrocks are commonlyformed at convergentboundaries
Igneous Activity andPlate Tectonics
• Felsic igneousrocks arecommonlyformed adjacentto convergentboundaries
• Intraplatevolcanism
– Hot Spots– Hawaii,
Yellowstone
Types of Sedimentary Rocks
• Clastic sedimentary rocks– Lithification
• Chemical sedimentary rocks
• Organic sedimentary rocks– Accumulate from remains of organisms
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Clastic Sedimentary Rocks• Breccia and Conglomerate
• Sandstone– Types determined by composition
• Quartz sandstone -• Arkose -• Graywacke -
Clastic Sedimentary Rocks• Shale
– Splits into thin layers (fissile)
• Siltstone– Lacks fissility
• Claystone– Predominantly clay-sized grains; non-fissile
• Mudstone
Chemical Sedimentary Rocks• Carbonates
– Limestone is composed mainly of calcite• Most are biochemical, but can be inorganic• Often contain easily recognizable fossils• Dolomite
• Chert
• Evaporites
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Organics in Sedimentary Rocks
• Coal
• Oil and natural gas
Metamorphic Rock Classification• Metamorphism
• Classification based on rock texture– Foliated (layered) vs. non-foliated (non-layered)
Types of Metamorphism• Contact metamorphism
– High temperature is dominant factor– Produces non-foliated rocks– aureole– (e.g., hornfels)– (e.g., marble)– (e.g., quartzite)
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Types of Metamorphism• Regional metamorphism
– High pressure is dominant factor– Results in rocks with foliated textures– metamorphic grade– Prograde metamorphism of shale produces:
• slate• phyllite• schist• gneiss
Hydrothermal Processes
Hydrothermal processes:– Metamorphism
• Water transmits ions between grains– Formation of hydrothermal rocks
• Serpentinite• Metallic ore deposits often form this way (veins)