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254 A POPULAR TREATISE ON GEMS.
blowpipe into a clear greenish glass ; borax and acids do not affect it.
Essonite is found in the sand of rivers, and in the primi-tive rocks of Ceylon, in considerable masses; also in Scotland.
It
is treated like garnet, by being cut on a copper plate with emery, and
polished on a tin wheel with rotten-stone. It also receives the form of
other gems, and when set, it is mounted with a foil answering to its
color.
It
is used for rings and breastpins. Essonite' is distinguished from
zircon by inferior hardness, smaller specific gravity, diminished
lustre, and simple refraction of light. Garnet is heavier, and idocrase
is lighter than essonite.
TOURMALINE, RUBELLITE, SIBERITE.
This
mineral is as yet very little known among jewellers and the trade in
general, although it has been in commerce for a number of years past,
but under other names, such as red tourmaline, or siberite, brought
from Siberia, and sold in the trade as Oriental ruby.
Tourmaline
was first introduced as a gem by the Dutch, who imported it from
Ceylon. Tourmaline occurs in crystals and crystalline masses, and its
forms are six, nine, and twelve sided prisms, with various truncations
and terminations, which commonly differ in the number and size of the
faces at the two ends. The crystals are long, striated, and complete,
or aggregated into irregular masses ; the fracture is conchoidal and
uneven, semi-transparent to opaque. It has double refraction of light,
which, however, is only visible in small pieces ; it has a
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