Loose Gemstones
Some Gem Stones Are Better Than Others: Which Gemstone is Best For Your
Project?
Rock and Mineral Hardness
Hardness is the resistance of minerals to scratching or abrasion. It is
one of the easiest properties to study and it is a very useful diagnostic
tool for the classification of unknown minerals. In 1812 a German
mineralogist, Frederich Mohs, devised a hardness scale of rocks by
selecting ten common minerals.
This scale, commonly known as the Mohs
scale, is now regarded as standard for the classification of rock
hardness. The table below lists the set of minerals selected by Mohs and
their hardness.
It is important to note that this is not a linear scale,
so for example, Corundum with a designated hardness number of 8 is twice
as hard as Topaz (hardness 7), but four times as soft as Diamond. There
are easily obtainable hardness sets to measure the hardness of unknown
specimens. If you have a reasonable number of rocks you can probably
assemble the scale from your own collection.
If you do not want to buy anything commercially to check hardness, you
can still get a long way in finding out the hardness of
your specimen if you know that:
• the hardness of 1 feels greasy and is very soft and powdery
• a fingernail has a hardness of about 2.5
• steel knife will scratch anything below 5.5
• any rocks and minerals of hardness 6 and above will scratch glass.
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