Physical Properties of Minerals In addition to the “characteristics” of minerals which are required for a substance to be a mineral, there are “physical properties” that help us determine which mineral is which. (Review: What are the fives characteristics of minerals?)

1. Hardness How easily the surface of a mineral can be scratched Harder minerals can scratch softer ones Can use Moh’s Hardness Scale (1 to 10) 1 = talc 10 = diamond

2. Color, Transparency, Luster Color cannot positively identify a mineral. The same mineral may have many different colors Both of these are the mineral flourite

Transparency Transparent: when you can see clearly through it Translucent: light comes through it but you cannot see clearly through it Opaque: no light comes through

Luster: how a mineral looks or reflects light Examples: glassy, metallic, pearly, waxy, earthy

3. Streak Many minerals will leave a colored powder when they are rubbed against an unglazed ceramic tile (streak plate) – called the streak

4. Cleavage and Fracture Cleavage: if a mineral breaks or splits apart with smooth surfaces in certain directions Fracture: if a mineral breaks with a rough or jagged surface

5. Specific Gravity Each mineral has a unique specific gravity which is a measure of density

Other Properties Reaction to HCl Double Refraction – makes double image Magnetism Angle between crystal faces

Some minerals are ORES A mineral is an ore if it contains a useful substance that can be mined at a profit. For example, hematite contains iron Bauxite contains aluminum (used in our foils, etc.) YouTube video on the history of aluminum mining: http://www.youtube.com/watch?v=qAKK4UIQryg

Gems Gems are valuable minerals prized for rarity and beauty Examples?