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Minerals
Definition: Minerals are . . . .
1. Formed in nature (not man-made)
2. Inorganic (not made of living matter)
3. Solid
4. Have definite chemical compositions. For example, the chemical
formula for quartz is always SiO2 .
5. Have particular crystalline structures (although they are often
microscopic).
There are over 3000 minerals known to exist in the earth’s crust.
About 100 of these are considered to be “common.”
Most rocks are made out of more than one mineral, although a rock
may be made out of just one mineral.
Mineral Formation
Minerals may be formed by either of 2 processes:
1. Cooling of magma
 As magma cools, atoms combine with each other to form minerals
 The chemical make up of the magma and pressure determine
which minerals will form.
 Cooling rate determines size of crystals.
slow cooling - larger crystals
fast cooling - smaller crystals
2. Precipitation
 Elements in liquid form are mixed in solutions, such as
underground water, or the ocean.
 When the liquid part evaporates, the elements left over crystallize.
 We say that the minerals precipitate from solution.