Minerals of the Earth

What is a mineral? What objects in this classroom are considered minerals? Mineral: naturally occurring, inorganic solid with a specific chemical composition and a definite crystalline structure. Minerals occur naturally and all minerals are inorganic (never alive) All minerals are solids (definite shape and volume) The chemical composition of a mineral is specific to that type of mineral Atoms arranged in geometric pattern that repeat; gives the crystalline structure of the mineral 6 major crystal systems: Table 4-1 Well defined crystals= formed in open space Density and hardness make each mineral unique

Minerals from Magma Magma: molten material found beneath the Earth’s surface Magma forced upward (density differences) where the magma cools; compounds interact chemically to form minerals Type and amount of elements found determine which minerals will form Rate of cooling determines the size of mineral crystals Magma cools slow: large crystals Magma cools quickly: small crystals form

Minerals from Solution Water in a solution can dissolve only so much of a solid before the water becomes saturated. If solution becomes supersaturated (overfilled) with another substance, mineral crystals begin to form Can also form when elements dissolve in supersaturated solution Ex: Gypsum deposits form from evaporated water

Mineral Groups Silicates: minerals that contain silicon and oxygen, and usually one or more other elements; 96% of minerals found in Earth’s crust EX: feldspar and quartz (most common minerals); unique structure accounts for the diversity of silicates Carbonates: minerals composed of one or more metallic elements with the carbonate compound EX: calcite, dolomite, and rhodochrosite; primary minerals found in rocks such as limestone and marble; distinct colorations Oxides: compounds of oxygen and a metal; hematite and magnetite are iron oxides (good source of iron); uraninite valuable for source of uranium (generates nuclear power)

Mineral Identification Hardness: most useful test; measure of how easily a mineral can be scratched. Measured using Mohs scale of hardness; determined by the arrangement of a mineral’s atoms. Cleavage & Fracture: determined by atomic arrangement; cleavage: mineral that splits relatively easily along one or more planes fracture: minerals that break with rough or jagged edges Density & Specific Gravity: reflects the atomic weight and structure of a mineral; useful identification tool; sometimes too small to tell differences; Color: caused by trace elements or compounds; least reliable clues to a minerals identity Luster: way a mineral reflects light from its surface; either metallic (shiny surfaces) or nonmetallic (do not shine like metals); caused by differences in chemical composition Texture: how feels to touch; often used in combination with other tests; smooth, rough, ragged, greasy, soapy or glassy. Streak: the color of a mineral when it is broken up and powdered; not always the same as the mineral color. Rarely changes; cant be used to identify all minerals (if harder than a porcelain plate)

Table 4-1

Special Properties Double refraction: refraction of a single ray of light into two rays creating two images (due to arrangement of atoms) Chemical composition: calcite fizzes when in contact with HCl; releases CO2 in form of bubbling gas Special properties of specific minerals aid in identification

Mineral Uses Ores: contains a useful substance that can be mined at a profit EX: hematite is useful ore that contains element iron ANY ITEMS MADE OF IRON IN THIS ROOM? ALUMINUM? Mines: ores located deep within Earth’s crust removed by underground mining. Necessary to get rid of the waste material before the ore can be used This process can be very costly and harmful to the environment

Gems These are valuable minerals that are prized for their rarity and beauty Rubies, emeralds, and diamonds (rubies & emeralds more valuable) Used for jewelry