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258 PRECIOUS STONES.
Mussa
Alp in the Ala Valley, the exact spot being called Testa Ciarva, a
locality already mentioned in conÂnection with Hessonite and Diopside.
When used as a gem, Idocrase is either step cut or table cut. There are
several minerals with which Idocrase may be confounded ; of these
Zircon and Demantoid Garnet are distinctly heavier, both are harder,
and Garnet is singly refracting.
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Quartz
(Cairngorm), Tourmaline and Diopside are lighter, Quartz and Tourmaline
being harder and Diopside softer than Idocrase. Axinite is slightly
less dense, slightly harder, and, more important, it shows violet,
brown and green colours in different directions. Olivine is rather more
yellow in colour, and is very feebly dichroic. Epi-dote is slightly
denser than Idocrase, slightly softer and strongly pleochroic, showing
green, yellow, and brown tints in different directions.
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