Calcite (CaCO3) and dolomite Many non-silicate minerals have economic value Hematite = oxide mined for iron ore Halite = halide mined for salt Grow in a cubic shape Sphalerite = sulfide mined for zinc ore Native copper = native element mined for copper Structure of minerals
Chapter 3: Matter and Minerals 15:40 Polymorphs Minerals with the same composition but different crystalline structures Diamond and graphite Phase change = when one polymorph changes into another (temperature or pressure) Physical properties of minerals Primary diagnostic properties Determined by observation or performing a simple test Several physical properties are used to identify hand samples of minerals Crystal form External expression of a mineral’s internal structure Often interrupted die to competition for space and rapid loss of heat Well-developed crystal faces do not always form in nature. Growth of many crystals inhibits development of crystal faces. Luster Appearance of a mineral in reflected light Two basic categories Metallic Pyrite Nonmetallic Other descriptive terms: vitreous, silky, earthy Quartz (vitreous, glassy) Color
Chapter 3: Matter and Minerals 15:40 Generally unreliable for mineral identification Often highly variable due to slight changes in mineral chemistry Exotic colorations of certain minerals produce gemstones Streak Color of a mineral it its powdered form Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness Cleavage Tendency to break along planes of weak bonding Produces flat, shiny surfaces Described by resulting geometric shapes Number of planes Angles between adjacent planes Amphiboles have two cleavages that intersect at 60 degrees Pyroxenes have two cleavages that intersect at 90 degrees Fracture: absence of cleavage Specific gravity (density) Weight of a mineral/weight of an equal volume of water Average value = 2.7 Reflects the packing of atoms and the average atomic weight of the constituent atoms Magnetism (magnetite) Reaction to hydrochloric acid (calcite) Malleability Double refraction Taste Smell Elasticity
Chapter 4: Igneous Rocks 15:40 Igneous rocks form by solidification of magma or molten (liquid) rock
Chapter 4: Igneous Rocks 15:40 In the crust 95% igneous rock 5% sedimentary rock On the surface 75% sedimentary rock 25% igneous rock The earth is mostly solid. Therefore, magma forms within the earth through melting. Molten (melted) rock is called magma Temperatures high enough to promote melting to produce magma occur in the mantle Magmas ascend because silicate liquids are less dense than equivalent solid rocks General characteristics of magma Rocks formed from lava are extrusive, or volcanic rocks Some magma reaches the surface and is extruded
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