Unit 5:

 Minerals are:  Solid  Formed in nature  Inorganic  Of a definite composition  Composed of a particular crystal structure

 Minerals are formed by natural processes  Minerals are Inorganic  Inorganic – not formed from living matter  Minerals are not living and never were living  Salt is a mineral, coal and sugar are not

 All minerals are solid – definite shape, definite volume  Most are compounds, some are elements  Contain same elements in same ratio  Ex: SiO 2

 Crystals are solids with repeating patterns  More space = better crystal formation

 Minerals can form from Magma  Magma – molten material found beneath Earth’s surface  If magma cools slowly in Earth’s heated interior, large crystals can form  If magma cools at Earth’s surface, or comes into contact with air or water, smaller crystals form

 Minerals can also form from a solution  Supersaturated solutions will cause crystals to precipitate  If the liquid of a solution evaporates, the remaining elements form crystals

 Silicates – Silicon + Oxygen + Metal(s)  Ex: Olivine - Mg 2 SiO 4

 Carbonates – CO 3 and Metal(s)  Ex: Calcite - CaCO 3

 Oxides – Oxygen and Metal(s)  Ex: Hematite– Fe2O3  Sulfates – SO4 and Metal(s)  Anhydrite CaSO4  Sulfides – Sulfur and Metal(s)  Pyrite – FeS2  Halides – Halogen (Cl or F) and Metal(s)  Halite - NaCl

 Minerals can be identified through several simple tests

 Color can be caused by trace compounds in a mineral  Color is one of the least reliable tests: Why?

 The way a mineral reflects light from its surface is called luster  Luster can be classified as either metallic or nonmetallic

 Texture describes how a mineral feels to the touch  Can be described as smooth, rough, ragged, greasy, soapy, or glassy

 Minerals rubbed on an unglazed porcelain plate may leave a colored, powdered streak on the plate  Streak is the color of a mineral when it is broken up and powdered  Streak may not match a mineral’s external color  Streak rarely changes, even after weathering  Minerals must be softer than a porcelain plate

 Hardness measures how easily a mineral can be scratched  Measured on the Mohs Hardness Scale  A mineral will scratch all elements with a softer hardness on the scale

 A mineral that breaks along one or more flat planes is said to have cleavage  Minerals that break with rough or jagged edges are said to have fracture

 The ratio of the weight of a substance to that of water is specific gravity  Density does nor depend on the amount of the substance, so it is very useful for identification

 Ores contain useful substances that can be mined for a profit  Ex: Bauxite – aluminum  Gems are prized for their rarity and beauty  Ex: Rubies