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Sillimanite
Sillimanite
is formed from aluminum silicate and is a transparent to translucent
mineral ranging from white to gray, brown and green. It is mostly
found as silky and fibrous masses with glassy luster. If it is not
fibrous, the best field indicators are its crystal habit, color,
brittleness and hardness.
Sillimanite is named after an American chemist and mineralogist,
Prof. Benjamin Silliman. For its fibrous inclusions, it is sometimes
also known as "fibrolite" in the jewelry world. Gem quality
sillimanite crystals are rare and is seen seldom at retail.
Blue variety of sillimanite is the most sought and is found only in
the ruby-rich Mogok areas of Burma. The gray to green variety is found
in Sri Lanka from the gem gravels. A third variety, usually used in
the creation of artifacts, is found in the Clearwater River Valley in
Idaho.
Sillimanite is basically used to manufacture mullite refactory
ceramics, spark plugs, and high temperature crucibles. For jewelry,
the chatoyant green and blue varieties are most suitable. The hardness
of the stone is 6 - 7 on Mohs scale and specific gravity, 3.23.
 
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Name |
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| Sillimanite |
6-7.5 |
3.25 |
e |
f |
g |
h |
i |
j |
k |
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