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The Hardness of Minerals

In 1822 Frederick Mohs devised a scale for the hardness (actually scratchability) of minerals from 1 (softest) to 10 (hardest). A stone with a higher hardness will scratch one with a lower hardness. While not strictly scientific it is so clever that it is still widely used. Medium numbers (½, ¼) are also used.

talc

Talc

H = 1

The softest stone.

Gypsum

H = 2

Used for Plaster of Paris.

Calcite

H = 3

Along one plane.

Fluorite

H = 4

Many colors.

Apatite

H = 5

From the Greek "to deceive" due to its many colors.

Orthoclase Feldspar

H = 6

Feldspar is the basis of clay.

Quartz

H = 7

The most common mineral.

Topaz

H = 8

Precious.

Corundum

H = 9

Red is ruby; blue and other colors are sapphire.

Diamond

H = 10

The hardest mineral.

You can easily build a set of these minerals.
You can also keep in mind the following common items that will sort out many minerals.

Fingernail

H = 2.5

Fingernail courtesy of Henry Francis, my nephew.

Copper

H = 3.0

Coins, tubing, wire.

Glass

H = 5.5

Window and drinking glasses. Not lead glass.

Tempered File

H = 6.5

Quartz and above not scratched.

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