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PRECIOUS STONES
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ANDALUSITE
Was named from the district in Spain where it was first discovered.
Chiastolite and made are varieties of this mineral. It is found in Spain, Brazil, and Ceylon.
Crystallization trimetric, in right rhombic prisms.
Hardness, 7 to 7.5; specific gravity, 3.1 to 3.32.
Lustre, when clear enough to cut for jewels, vitreous; translucent to opaque; tough.
Cleavage lateral, distinct.
Dichroic,
sometimes trichroic; twin colors, Green : green, red, yellow; brown:
reddish brown and greenish yellow. The colors are similar but not. as
strong as in the alexandrite.
Composition: silica, 36.9; alumina, 63.1.
Infusible before blow-pipe, but with borax melts with extreme difficulty.
Gems show mixed colors of green, brown, and yellow; opaque variety is gray to flesh-red.
But
little is found sufficiently transparent to cut for gems. Many stones
sold as andalusite are brown tourmalines cut from twin-colored
crystals. They are much more magnetic by friction than the andalusite,
readily lifting small pieces of tissue paper, cotton, and the like,
after being rubbed on a woollen sleeve.
Usually cut step.
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