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Properties of Minerals

Quartz
Courtesy of Gregory D. Holland

Pyroxene
Amethyst Galleries, Inc.

Hematite
Wayne State University
Several properties allow us to determine which mineral we have collected. The color may vary because of slight impurities. A less variable property is hardness. The resistance of a mineral to scratching is rated on the Mohs hardness scale from 1 (very soft) to 10 (very hard). Another property is how the surface of the mineral reflects light, or its luster. The density of a mineral lets you know if it feels heavy or light for its size. Density is the mass of a rock divided by its volume (grams per cubic centimeter).

Measuring Hardness

You can use the following items to estimate the hardness of a mineral:
your fingernail: hardness of 2.5
a penny: hardness of 3.0
a knife blade: hardness of 5.5

How to Perform the Hardness Test

Select a fresh mineral surface.
Try to scratch the mineral with the point of an object of known hardness.
Press the object firmly but lightly against the unknown mineral. If the object is harder than the mineral, you should see and feel a definite scratch. Inspect the mineral for a new line etched into the mineral surface.
Repeat with a softer object to see if it also will scratch the mineral.
Keep testing until you have an object that scratches the mineral and an object that doesn't scratch. Start at the higher (harder) end of the scale and work down. The hardness of your mineral is between the hardnesses of the two known objects.
For example, a mineral can be scratched by a knife (5.5) but not by a penny (3). Therefore, the mineral has a hardness of about 4.

A mineral of a given hardness will scratch a mineral of less hardness.

Mohs Hardness Scale

Minerals that have a specific hardness are given below, from 1 (softest) to 10 (hardest):


1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond

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