GEMS AND PRECIOUS STONES. 73
Malachite
is
a hydrous carbonate of copper, having a green colour, and belongs to a
different class of minerals that have been used for ornamental
purposes, both in ancient and modern times. It is mostly found massive
or incrusting, and with a smooth mammilatcd or botryoidal surface. The
different green colours arc usually distributed in a banded concentric
manner; these bands showing successive deposits of the mineral, and
have in most cases resulted from the percolation of water through
copper-bearing rocks, and the subsequent deposition of the dissolved
carbonate of copper.
Although
it has been very largely used for decorative work and small ornamental
articles, it is too soft to be of much value for jewellery, having a
hardness of 35—4, a specific gravity, 3'7—4, and crystallizing in the
mono-clinic system when thus found. It dissolves with effervescence in
acids (presence of carbonic acid), and when heated on charcoal is
reduced to metallic copper.
Theophrastus
states that a species of stone comes from the copper-mines, and is
called false emerald. This most probably refers to our malachite. The molochites of
Pliny, obtained from Arabia, having a deep green colour, and nearly
opaque, is also probably our malachite. The name malachite is from moloche or malache, meaning marsh-mallow, and refers to its green colour.
The
finest specimens come from Nijni-Tagilsk in Siberia, from mines
belonging to the late Prince Demidoff. One block from this locality was
obtained measuring 16 feet long, 7-1/2 feet wide, and 3-1/2 feet
thick, of very good quality. The exhibit from this locality at the
London Exhibition of 1851, consisting of doors and vases, created quite
a sensation, and directed public attention to this material for
decorative work. In Russia, furniture and household fittings are often
covered with veneer made of malachite, and in the collection at St.
Petersburg there is a mass of 3-1/2 feet square, of a fine
emerald green colour, weighing 90 lb., and stated to be worth £82,000.
At Versailles there is a room, the furniture and ornaments of which are
of malachite. There are many other ornamental works of historic
interest made of this material, but it is not likely that its use will
become general.
Besides
the Russian localities, some fine specimens have been obtained at the
Burra Burra mines of South Australia, and it is common in many other
countries. Some very delicate specimens of this mineral have been
obtained at the Cobar mines of this Colony, but not fit for ornamental
purposes.
Iron Pyrites
"Was
largely used for jewellery during the eighteenth century, and although
taking a fine polish, is of very little value. It was used by the
ancient Mexicans with turquoise and obsidian for decorative purposes.
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