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Minerals
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Minerals Natural, usually inorganic solid that has a characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties.
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Is it a Mineral? Is it organic? Does it occur naturally?
Is it a crystalline solid? Consistent chemical composition? Must answer yes to all 4 questions for it to be a mineral
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10 Most common minerals Quartz Calcite Orthoclase Dolomite
Plagioclase Halite Muscovite Gypsum Biotite Ferromagnesian Calcite Minerals These make up 90% of Earth’s mass
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Mineral Groups Silicates 96% of Earth’s crust Contains Si and O
Can have other elements also Feldspar – Orthoclase if K, Plagioclase if Na or Ca Ferromagnesian minerals – rich in Fe
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Mineral Groups Nonsilicate Minerals Do not contain Si and O Six groups
Can contain one or the other, but not both Six groups Carbonates Native elements Halides Oxides Sulfates Sulfides
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Crystalline Structure
Crystal – atoms, ions, or molecules are arranged in a regular, repeating pattern Silicate crystal structure Silicon – oxygen tetrahedron 1 Si with 4 O’s around it Basic building block of silicates Can be connected 6 different ways
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Crystalline Structure
Nonsilicate crystals Diverse chemical composition leads to variety of crystal structures Cubes, hexagonal prisms… Crystal structure influences physical properties Native elements are dense due to compact crystal structure
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Silicate Tetrahedron
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Physical Properties of Minerals
Mineralogist Examine, analyze, and classify minerals Result from chemical composition and crystal structure Can be useful in identifying minerals
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Physical Properties Color Not reliable for ID purposes
Small amount of impurities can affect color Weathered surfaces may hide color Only look at fresh surfaces
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Color
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Physical Properties Streak Color of mineral in powder form
Streak plate – unglazed ceramic tile Streak color may differ from mineral color Metallic minerals – darker streak Nonmetallic minerals – lighter streak
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Streak
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Physical Properties Luster Light reflected from mineral’s surface
Metallic luster – shiny surface Nonmetallic luster Glassy Waxy Pearly Brilliant Dull / Earthy
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Metallic Luster
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Glassy Luster Quartz
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Waxy Luster Variscite
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Pearly Luster Talc
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Brilliant Luster Diamond
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Dull / Earthy Luster Psilomelane
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Physical Properties Cleavage / Fracture Cleavage Fracture
splitting along specific lines of weakness Forms smooth, flat surfaces Fracture Break unevenly into pieces Forms curved, irregular surfaces Conchoidal fractures – curved surface
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Cleavage - Calcite
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Fracture Conchoidal
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Fracture Irregular
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Physical Properties Hardness Ability to resist scratching
Mohs Hardness Scale Scale of 1 to 10 1 = Talc 10 = Diamond Glass is about a 5
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Mohs Hardness Scale
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Physical Properties Crystal Shape Density 6 Basic shapes
Certain minerals always form crystals with the same shape Density Ratio of mass to volume Can help identify minerals
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Crystal Shapes
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Physical Properties Fluorescence and phosphorescence
Chatoyancy and asterism Double refraction Magnetism Radioactivity
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Double Refraction
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