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549. APATITE—JET.
Apatite occurs
in a variety of colours that may give it, when cut, an appearance
similar to several other minerals used as gems. The usual colour is a
pale green, but blue, violet, red, yellow, and brown are sometimes seen
in this species. It is transparent to opaque, but the transparent kinds
are the only ones used for cutting. The lustre is vitreous, and the
mineral shows weak double refraction, the indices for yellow light
being 1.646 and 1.642 ; it shows pleochroism in the more deeply
coloured specimens. Sometimes a chatoyant reflection is seen on the
basal plane. The specific gravity is 3"16 to 3'22 ; the mineral is
brittle, shows a conchoidal fracture, and has two imperfect cleavages,
one parallel to the basal plane, and the other a prismatic cleavage. It
occurs in crystals, often highly modified, belonging to the hexagonal
system. It is a calcium phosphate, with fluorine or chlorine,
It is found in good specimens at Ehrenfriedersdorf in Saxony ; pale,
yellow and pale green crystals occur in the Zillerthal, and in Mosedale
in Cumberland ; the deep green variety is found at Arendal in Norway,
in Siberia, and in Canada. Canada also yields a rose red type at St.
Eoch ; and red and green crystals are found at Auburn in Maine in the
United States. Its specific gravity and softness distinguish it from
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