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164
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PRECIOUS STONES
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ZIRCON
A colorless variety
of this stone, with a smoky tinge, is called jargoon, and that name has
of late been given also to the deeper shades of brown. The true
hyacinth is the zircon of a decided red color, and the jacinth is
another shade. These names have been used commercially of late, to
designate certain colors of the essonite tribe of garnets, which are
now known commonly as hyacinths and jacinths. It is found in Ceylon,
Germany, France, Bohemia, America, India, Arabia, and Australia.
Crystallization dimetric; in quadrilateral prisms, terminating in a pyramid at both ends.
Hardness, 7.5; specific gravity, 4.1 to 4.9.
Lustre vitreous to adamantine; transparent to opaque.
Cleavage imperfect; fracture conchoidal, brilliant.
Double
refraction (index, 1.97 and 1.92) to a high degree ; dichroism very
weak, weaker than any other; positively electric when polished;
phosphorescent when heated.
Composition: Zirconia, 66 to 76; silica and oxide of iron, 24 to 34.
Melts
with borax to glass; sulphuric acid affects it at length after
maceration; infusible before the blow-pipe, but loses color.
Color, brown of all shades, red, violet, yellow, and green; streak uncolored.
Cut brilliant and step, mostly brilliant in this country.
Under
the microscope the zircon has a watery appearance, which is called in
Europe " ratine." It approaches the diamond in appearance more closely
than any other stone.
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