Minerals A mineral is a naturally occurring inorganic

Minerals • A mineral is a naturally occurring, inorganic, crystalline substance with a specific chemical composition • Elements Minerals Rocks • Over 4, 000 different minerals

• Minerals form by the process of crystallization. Microscopic crystals are the first to form and then may grow larger, maintaining their crystal faces if allowed to • Crystallization of minerals may occur by lowering the temperature of a liquid, precipitation, or by reheating causing rearrangement of atoms/ions

• Two factors control the type of mineral that forms: 1) Chemical composition 2) Pressure-Temperature – Polymorphs are minerals that have the same chemical composition, but different crystal structure Density Hardness Elec. Prop. Visual Prop. Crystal Struc. Graphite 2. 1 g/cm 3 Soft Conductor Opaque Hexagonal Diamond 3. 5 g/cm 3 Very Hard Insulator Transparent Cubic

• Physical properties of minerals are used for identification. 1) Cleavage – Planes of easy breaking, which are based on weaknesses in the atomic structure. Minerals can have 1, 2, 3, 4, or 6 planes of cleavage

2) Hardness – Ability of the mineral to resist scratching. Tested using known minerals and common items

3) Luster – The way a mineral reflects light. Can be either metallic or nonmetallic Examples: Metallic Aluminum foil Gold ring Steel nail Nonmetallic Plastic Glass Ceramics

4) Streak – Color of the mineral powder. Tested using streak plates

5) Reaction to HCl – Used to distinguish calcite from other minerals

6) Taste – The mineral halite exhibits a characteristic salty taste 7) Color – Unreliable for some minerals (quartz), diagnostic for others (olivine) 8) Specific Gravity – A unitless number representing an approximate density. Metallic minerals usually have a higher specific gravity than nonmetallic minerals