CHAPTER XV.
VARIOUS PRECIOUS STONES —continued
Zircon.
Zircon appears
to have been first discovered by Klaproth in 1789, in the form of an
earth, and six years later he found that the stone hyacinth contained a
similar substance, both having the formula, ZrSiO4, and
both having as their colouring agent ferric oxide. There are several
methods of obtaining the metallic element, zirconium : it is however
with the silicate of zirconium that we have to deal at the moment. This
is called zircon, ZrSiO4, or hyacinth when transparent or
red. but when smoke-coloured, or colourless, it is the jargoon. or
jarcon, and is found in silt and alluvial soils, limestone, gneiss, and
various forms of schist, in India, Australia, the Urals, and certain
parts of America. It is often combined with and found in juxtaposition
to gold and certain varieties of precious stones. The lines of cleavage
are parallel to the sides of the prism, and the crystals have an
adamantine, or diamond lustre, varying from the completely opaque to
the transparent. In some varieties the oxide of uranium is also present
in traces. It crystallises in the 3rd (tetragonal) system, with indis-
