Ch. 4 Minerals Define a Mineral A solid with a specific chemical composition and a definite crystalline structure. There are over 3000 minerals Minerals occur naturally. What does this mean? They weren’t made synthetically. Most minerals are in the form of a compound. Can you list some that are not compounds? Cu, Ag, S, Pb, Sn, Au. The ratio of elements in a certain mineral may vary. There are 6 major crystal systems . Table 4-1 (pg. 78)

Some minerals form from magma – molten material below the Earth’s surface. The rate at which it cools determines its size. Minerals can form from supersaturated solutions, also. Of the 3000 minerals in the Earth’s crust, there are only 30 that are commonly found. Silicates = SiO2 (sand) Forms from silicon and oxygen Fig. 4-5(pg. 81) – various types Carbonates = a metallic element forms with CO3. Limestone, coquina, and marble. Oxides = compounds with a metal and oxygen. Hematite, magnetite

Identifying Minerals 1. Color- not always reliable for mineral identity. 2. Luster – its ability to reflect light. Metallic or nonmetallic Ex. Metallic – silver, copper, galena Ex. Nonmetallic – quartz, sulfur, calcite, gypsum 3. Texture – smooth, rough, ragged, greasy, soapy, glassy. 4. Streak – residue left after scrapping across a porcelain plate. Fig. 4-10 (pg. 85) 5. Hardness – how easily it can be scratched. Table 4-3 (pg. 86)

6. Cleavage & Fracture – if a mineral splits easily and evenly along one or more planes then it has cleavage. Minerals that break with rough or jagged edges have fracture. Fig. 4-11 (pg. 87) 7. Density & Specific Gravity – the difference in mass in a given volume is the minerals density (D=m/v). Specific gravity uses a ration of the minerals weight to the weight of an equal volume of water (buoyancy). 8. Special Properties Ex. Calcite bends light as it passes through – Fig. 4-12 (pg.88) Ex. Magnetite is naturally magnetic – Fig. 4-13

Mineral Uses Ores – minerals that contain a useful substance that is mined for a profit. Hematite  mined for iron Bauxite  mined for aluminum Mines – underground or strip mining above ground. Gems – valuable minerals that are known for their rarity and beauty. They are usually cut and polished and sold as jewelry. Ex. Diamonds, emeralds, rubies Fig. 4-16 (pg.91)