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Definition of a Mineral Minerals The Geologic Alphabet • • • • Natural Crystalline Solid Inorganic Chemical Compound Source: E. R. Degginger/Bruce Coleman Inc. Mineral Formation Form Igneous Rocks Primary 1. Crystallize out of a magma 2. Crystallize out of water Form Sedimentary Rocks Physical Properties of Minerals A. Mineral Shape Secondary 3. Chemical Weathering 4. Metamorphism Form Metamorphic Rocks Crystal Form Aka crystal habit Source: Jeffrey Scovil Fracture Quartz: Conchoidal Mineral Cleavage Mineral Cleavage Halite - 3 planes; angle 90° Muscovite - 1 plane; angle N/A Source: Ed Degginger/Bruce Coleman Inc. Source: Breck P. Kent Mineral Cleavage Fluorite: 4Fluorite planes; not 90° Physical Properties of Minerals B. Mineral Appearance Color Quartz Color Quartz Powder Streak (Powder Color) Luster Hematite Metallic Highly reflected and “metal colored” Nonmetallic Vitreous Varies Pearly Shines like glass Resinous Whitish iridescence (like a pearl) Dull shine (like wax) Earthy (Dull) Surface doesn’t reflect light Source: Breck P. Kent Metallic Luster Nonmetallic Luster - Vitreous Quartz Source: E. R. Degginger/Earth Scenes Nonmetallic Luster - Earthy Optical Properties 1. Opaque 2. Translucent 3. Transparent Source: Breck P. Kent Mohs Hardness Scale Physical Properties of Minerals C. Mineral Strength/Density Specific Gravity (Density) Magnetism (Magnetite) Reaction to HCl (Calcite) Physical Properties of Minerals D. Other Properties Taste (Halite) Striations & Banding Smell (Sulfur) Fluorescence - White light Source: Breck P. Kent Feel (Talc) Fluorescence - UV light Piezoelectricity Source: Breck P. Kent Petrologic Microscope (optical properties) Polarized Light - Calcite Biotite in white light Native Elements Mineral Families Oxides Hematite Pyrite Sulfides Gypsum Sulfates Carbonates Silicates: SiliconOxygen Tetrahedron Calcite Important Silicates Muscovite Feldspars Micas Mafic Minerals (rich in Fe & Mg—high temp) Orthoclase vs. Quartz Olivine Felsic Minerals rich in feldspar & silica—low temp