|
PRECIOUS STONES. 243
though
now the solid material is not so often used as thin slices, which are
veneered on. It is largely used, too, for mosaics and in the
ornamentation of luxurious buildings such as the palaces of the Eussian
Czars. Formerly it was the sole source of the beautiful pigment
ultramarine, which was greatly esteemed on account of the purity of its
colour and permanence. Now, however, the pigment is made artificially,
though the artificial product does not command nearly the same price.
All the substances that Lapis Lazuli is likely to be mistaken for are
of a higher specific gravity. Stained Agate is also harder, and the
carbonate of copper, Azurite, is softer.
370. Garnet.
The
term Garnet includes a series of isomorphous compounds, all of which
have, besides a very closely related chemical composition, very similar
physical properties.
The
name seems to have been derived from " Grenat," which really referred
to Hyacinth, a variety of Zircon. It was known in ancient times, for
Theophrastus describes a mineral, that was almost certainly Garnet, as
being used for mirrors. The " feminine Carbunculus " of Pliny probably
included some of the Garnets, his Amethystizontes being probably
Almandine Garnets.
The
predominant colour of Garnet is some shade of red, but amongst the
various kinds of the mineral, yellow, green, purple and brown are seen,
and some are colourless and some are black ; blue is never seen. The
colours will be more particularly referred to when dealing with each
kind separately; the lustre varies from a brilliant vitreous lustre to
a resinous; transparent to opaque; normally singly
e 2
|
||
|
|
||