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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)