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AXINITE.
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AXINITE.
Although almost a curiosity among gem-stones, yet fine crys­tals of axinite have been cut for ornamental use. It belongs to the triclinic system. The hardness of axinite approaches that of rock crystal, but the brittleness of this substance almost precludes its being cut. It looks well en cabochon, and incurs in that form less liability to fracture. The specific gravity of transparent flaw­less axinite is 3-29 ; its colour ranges between a pale puce, a plum, and clove brown ; it is generally strongly pleochroic, showing a white or straw yellow, an olive, and a violet or purple image in different directions. The best specimens are found at St. Christophe in Oisans, Isere. The presence of boron in axinite is remarkable : tourmaline is the only other gem-stone in which the element occurs. The percentage composition of axinite approaches—
Sphene.
This mineral, when it occurs in sufficiently large crystals and is perfectly transparent, is occasionally cut as a gem-stone. Some beautiful specimens, chiefly of a honey-yellow or greenish-yellow colour, have been obtained from various localities in Tirol, the United States and Canada. Sphene or titanite is calcium silico-tungstate and is remarkable, not only for its dichroism, but also for its strong dispersive power ; a brilliant-cut stone is full of " fire." The specific gravity of sphene is about 3*5, but its hardness is low, just under 5-5. Sphene contains in 100 parts about :
Cassiterite, Rutii.e, and Anatase. These are binoxides, cassiterite or tinstone being that of tin, the two others being distinct forms of titanium binoxide. .Cassiterite