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Specific gravity
Conductivity
Crystal systems
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| THE PHYSICAL PROPERTIES of
gemstones, their hardness, their specific gravity or density and they way
they break, depend on chemical bonding and the atomic structure within the
stone. For
example, diamond is the hardest natural material known, and graphite is one
of the softest, yet both are made of the same element, carbon. It is the way
in which the carbon atoms are bonded together in diamond that gives it a
greater hardness and resilience |
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HARDNESS
Gemstones are often tested by
using the Mohs’ hardness scale to determine just how hard they are. The
harder minerals are more durable in that they do not scratch easily and will
hold up better in jewelry. Talc is the softest mineral with a hardness of 1
and can be easily scratched with a fingernail. The gemstones with a rating
of 7 or over are relatively hard. Quartz gemstones (citrine, amethyst, etc.)
range in the 7's, topaz rates 8, and corundum (sapphires and rubies) are a 9
on the Mohs' hardness scale. Diamond registers a 10 and is the hardest known
naturally occurring material on earth, more than ten times the hardness of
corundum at 9. There is more of a spread between the gems and minerals found
between 2 and 3 and between 5 and 6, however corundum is only about 10 per
cent harder than topaz.
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SCALES OF HARDNESS Knoop scale
This scale shows the indentation caused by a diamond point when it meets
the surface of a mineral. The 10 stages correspond to Mohs' point
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| Mohs' scale of hardness
The Mohs' scale was devised by the German mineralogist Friedrich Mohs as
a means of classifying the relative hardness of minerals. He took ten common
minerals and put them in order of "scratchability ": each one will scratch
those below it on the scale, but will be scratched by those above it.
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Natural Gemstones |
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