Scientists identify minerals according to the following criteria:

  • Hardness
  • Density
  • Specific Gravity
    • how its density compares with the density of water
    • The density of water is 1.0g/cm3 (1 gram per cubic centimeter of water)
  • Color
  • Luster
  • Streak
  • Cleavage/Fracture
  • Crystal Shape.

Hardness is the ability of a mineral to resist being scratched. To determine a mineral's hardness, rub the mineral against another known mineral or object to see if it will become scratched.
The following chart indicates how you might test a mineral for hardness using a combination of Friedrich Moh's and field hardness scales. 1 represents the softest mineral while 10 is used for the hardest mineral. A mineral is able to scratch a mineral with a lower number and can, therefore be scratched by a mineral with a higher number.
(The links are to photographs of samples of the minerals. Place your mouse over each image link to view it in a separate window. Close the window to return to this page and continue.

HARDNESS SCALE (Moh's and Field Hardness Scales)
Hardness Item(s) That Will Scratch Mineral Mineral
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

A mineral's density is the amount of matter in a given space (mass/volume). Each mineral has a characteristic density (density does not vary with the size of the mineral). Specific gravity is the ratio of the density of a mineral compared to the density of water. It is a more specific way to compare the densities of minerals.

Color is easily observed, but not always a reliable characteristic for the identification of minerals. A number of different minerals have the same color.
A mineral may come in a variety of colors or may even change color due to the environment.

A mineral's luster describes the way light is reflected from its surface. Examples of luster include - metallic, nonmetallic, brilliant, glassy, greasy, pearly, or silky.

The streak of a mineral is the color of the powder left behind when the mineral is rubbed against a hard, rough surface (e.g. streak plate). A mineral's streak color may differ from the color of the mineral itself. This characteristic is most useful for minerals that are relatively soft (have a hardness less than 7) and which have a characteristic streak color.

These two characteristics describes the way a mineral breaks -
*cleavage - means to break along a smooth, definite line
*fracture - refers to rough, uneven breakage

rystal shape results from the pattern formed by the atoms of a mineral when it is forming. Most minerals have a characteristic geometric shape.

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Updated July 25, 2000 by: Glen Westbroek
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