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MINERALS
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What is a mineral? Naturally occurring, inorganic solid with an orderly crystalline structure and chemical composition 1. Naturally occurring = by natural geologic processes (ex: cooling of feldspars in magma) not man made; cubic zirconium) 2. Solid 3. Orderly, repetitive structure (in terms of arrangement of atoms; Opal or glass are not minerals for this reason). 4. Definite chemical composition (represented by chemical formulas like SiO2 ) 5. Generally inorganic (not produced from living things; CaCO3 = calcium carbonate or Calcite is an exception; makes up shells of marine animals).
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Mineral Formation 1. Crystallization from magma - Iron, magnesium, and calcium minerals 1st; then sodium, potassium, quartz minerals 2. Precipitation of solid mineral when water evaporates out. 3. Pressure and temperature - cause metamorphism = changes in pressure and temperature that allow minerals to migrate and react with each other in new ways --> form new minerals. 4. Hydrothermal Solutions - Hot mixture of dissolved substances
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Physical Properties of Minerals
- depends on chemical composition and crystal composition Color Streak Luster Crystal Form Cleavage/Fracture Density Hardness
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Color: Helpful, but not nec
Color: Helpful, but not nec. diagnostic; some minerals have a colored varieties Corundum’s structure is the same. Trace amounts of different element produce a variety of colors. Red = Ruby; Blue = Sapphire
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Streak: color of mineral in powdered form
Tested by… Streak plate – rub mineral across white tile. hematite Streak not nec. Same as color. only useful for metallic minerals
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Luster = How mineral’s surface reflects light
Metallic Luster (= like metal) Galena Pyrite Non-Metallic Luster: (Vitreous = like glass) Halite & Quartz
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Crystal Form: How atoms are arranged internally
Platy minerals = flat like sheets (ex. Muscovite) Hexagonal = quartz Calcite = rhomboid Galina = cubes Diamond (C) Graphite (C)
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Hardness: Resistance to being scratched
Can be scratched by glass, but not penny = Moh’s hardness of 4-6
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Cleavage & Fracture: tendency of a mineral to break along flat, even surfaces
Cleavage: Minerals break along the planes of their weak bonds. Perfect Cleavage = Micas (muscovite & biotite) = cleave along 1 plane. Results = sheets Halite = 2 cleavage planes Fracture: uneven breaking of mineral surface; conchoidal - no cleavage pattern
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Cleavage
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- will fizz in calcium minerals.
Reaction w/ acid - will fizz in calcium minerals. Calcite (CaCO3) = vigorous reaction on all surfaces Dolomite (Ca,Mg)CO3= mild reaction on powder; scratch then add acid
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Density = mass/volume (gm/cm3; typical range 2 to 8 gm/cm3)
Magnetism (magnetite) – Contains iron Flourescence = Minerals give off wavelengths in U.V.
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