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Download Ch 2.2 Notes - North Mac Schools
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Minerals Aluminum Silicate minerals Iron pyrite Calcium carbonate 2.2 What is a Mineral? Mineral – a natural, inorganic, solid found in Earth’s crust Characteristics of Minerals: • Naturally occurring (a diamond made in the lab is not considered a mineral!) • Solid • Inorganic – NOT made up or produced by living organisms or their remains • Definite chemical composition – Example: Halite is always NaCl • Definite crystal structure (Note: obsidian is melted basalt) Crystal – a natural shape of specific geometric arrangement NaCl = Halite How Minerals Form 4 Major Processes… Crystallization from magma 1st minerals to crystallize from magma; rich in iron, calcium, and Mg Precipitation limestone dissolved minerals precipitate out of solution Changes in pressure and temperature exposed to high pressure and extreme temperatures mica Formation from hydrothermal solutions dissolved minerals in extremely hot (100-300°) Bornite, sulfur Mineral Groups Silicate Minerals All minerals are classified as either Silicate or Non-silicate. Silicate minerals make up 96% of the Earth’s crust! All silicates have both silicon (Si) and oxygen (O). Quartz: SiO2 Most silicate minerals contain other types of atoms. Feldspars are the most common silicate minerals. The feldspar that forms depends on which metal combines with the SiO2 Orthoclase – K (potassium) Plagioclase – Na, Ca (sodium &/or calcium) Kinds of Minerals • Scientists have identified over 3000 different minerals. • The most common are called “Rock-forming” minerals There are 20 “Rock-forming” minerals. 10 of these make up 90% of the Earth’s crust... quartz calcite orthoclase dolomite plagioclase halite muscovite gypsum biotite ferromagnesian minerals Feldspar and Quartz alone make up >50% of the Earth’s crust. Ferromagnesian minerals are rich in Fe and Mg... Including: hornblende olivine muscovite biotite Crystalline Structure Crystal – A natural solid with a definite shape Silicates form in chains, sheets, and networks Silicon-oxygen tetrahedron Nonsilicate Minerals 4% of the Earth’s crust 6 major groups, based on chemical composition (page 158-159) Carbonates CO3 Halides Oxides O (w/o Si) Sulfates Na, K, or Ca with Cl or F SO4 Native elements Sulfides Element combined w/S Video on Minerals http://www.youtube.com/watch?v=8a7p1NFn64s (~10 min) 9.2 Identifying Minerals Characteristics of Minerals Mineralogists conduct tests to identify minerals. Color Some minerals have a distinct color, Sulfur Azurite Cinnabar Serpentine ...but generally, color is unreliable in identification. All corundum Luster - Light reflected from the surface of a mineral Metallic luster – reflect light Nonmetallic luster – glassy, waxy, pearly, brilliant Earthy - dull Streak – color of mineral in powdered form Rub mineral against an unglazed tile Cleavage and Fracture Cleavage – tendency to split along a plane Fracture – does not break along cleavage planes Moh’s Scale of Hardness Measure of the ability of a mineral to resist scratching Scratch Test: Fingernail, Copper, Steel, Glass, Quartz See scale on p. 165 Crystal Shape There are 6 basic crystal systems: Isometric or Cubic pyrite Triclinic turquoise Hexagonal , quartz Monoclinic, mica Orthorhombic topaz Tetragonal, zircon Density – ratio of the mass to volume Find mass: use an electronic scale Unit – g Find volume: measure with a ruler, or by Unit – cm3 Density Unit is g/cm3 Special Properties Magnetism Double refraction loadstone Fluorescence Glows under UV Phosphorescence Absorb UV then reemits Radioactivity
