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Chapter 5 1. 2. 3. 4. Inorganic Occurs naturally Crystalline solid Consistent chemical composition Gypsum Fluorite Ice? Salt? Sugar? Charcoal? Rock? Scientists have identified 3,000 minerals Of those minerals, there are 20 common rock-forming minerals All minerals are divided into 2 main groups: Silicate and Nonsilicate Minerals Silicates Nonsilicates Must have Silicon and Oxygen Usually has additional elements like Ca, Na, K, Fe, or Mg 96% of Earth’s crust Quartz and feldspar make up more than 50% of the crust Do not contain silicon and oxygen Make up 4% of Earth’s crust There are 6 major classes Mineralogists identify minerals based on a number of specific physical properties: Color Streak Luster Cleavage and Fracture Hardness Crystal Shape Density Easy to observe Unreliable Trace amounts of elements can change color Weathering can change color The same mineral can come in different colors. Rubies are cut from corundum with traces of Chromium (Cr) Sapphires are cut from corundum with traces of Cobalt (Co) Color of the mineral in the powder form More reliable than color Use a streak plate Minerals that are harder than the streak plate will leave no streak because it is too hard to rub off on the plate Light reflected from the mineral’s surface Metallic luster Nonmetallic luster: waxy, pearly, glassy, dull/earthy, or vitrious/brilliant Cleavage is the tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces Cleavage in three directions. Example: CALCITE Fracture is when the mineral does not split along cleavage planes Fracture can be irregular, fibrous, or conchoidal A measure of the ability of a mineral to resist scratching Hardness relates to the strength of bonds between the minerals atoms (Ex: Diamond vs. Graphite) To determine an unknown mineral’s hardness, you need to scratch it against a mineral of known hardness TETRAGONAL, ORTHORHOMBIC, HEXAGONAL, TRICLINIC, MONOCLINIC, ISOMETRIC Ratio of mass to volume of a substance Density = mass/volume Lead Most minerals have a density between 2 and 3 g/cc Density = 11.35 g/cc Galena Density = 7.6 g/cc Fluorescence – ability to glow under UV light Double Refraction – light is bent to produce a double image Magnetism Radioactivity