Hardness of Minerals

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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 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 help 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 Windows, drinking glasses. Not lead glass.		Tempered File H = 6.5 Quartz and above not scratched.

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