Minerals are classified according to: Hardness, Specific Gravity (how it compares with the density of water), Color, Luster, Streak, Cleavage and Crystal Form.

The following minerals are categorized according to Hardness. The following chart indicates how you might test a rock for hardness according to Friedrich Moh's scale. 10 is the hardest, and 1 is the softest mineral. (Links are to photographs of the minerals.)

The number at the left indicates the "hardness" of the crystal. The next column has the hardness item that will scratch the Representative Mineral (found as a link at the right). (Use your browser's back button to return to Sci-ber Text.)

1	Fingernail	Talc
2	Fingernail	Gypsum
3	Penny	Calcite
4	Penny	Fluorite
5	Glass, Knife blade, or Nail	Apatite
6	Streak Plate	Feldspar
7	File	Quartz (massive type) Quartz crystal
8	File	Topaz
9	File/Diamond	Corundum
10		Diamond