Rewa Kantha produces camelian and agate. Camelian is also obtained from Rajpipla.
Madras.—Godavary river, near Rajahm'undry—agate, jasper and camelian pebbles.
Onyx.—Occurs in Bombay in Nawanagar in bedded lavas.
Industry and marketing, etc.—The
most important and well-known place where agate and camelian are cut
and prepared for market is Cambay, in the Bombay Presidency. Other
centres for agate cutting are at Jubbulpore, C.P., Banda in the U.P.
and at a few minor places within the range of the Deccan trap. Cambay
also supplies most of the agate supplied in Europe. Large quantities
are also exported to China.
The
crystalline varieties, rock crystal, amethyst, etc., find their use in
jewellery in several parts of India, as for instance in Tanjore '
Vallam diamonds', near Kalabagh and Mari—'Mari diamonds', and also in
Kashmir. In N.W. India, rock crystals are also cut into cups, trinkets,
ornamental objects and sacred objects like lingams, etc.
Opal.—The
opal was regarded as a very precious stone by the ancients, and it was
next in rank to emerald. It was not popular for some time, but is now
getting popular. The finer varieties are very highly valued. It is
amorphous and has no crystal form. It consists of silica like quartz
but contains water in addition. It is a dried up silica jelly. It forms
compact and irregular masses in veins and cavities. Fracture
conchoidal. Hardness = 5-1/2 to 6-1/2 and is comparatively soft.
Specific gravity = 1-95 to 2-30. It wears quickly but could be
repolished. Lustre: Vitreous, dull or greasy, and transparent to
opaque. Colour varies greatly, being white, yellow, brown, red, pink,
green, grey or black. Precious varieties have a play of colours due to
the interference of light. (See Spencer, pp. 202-203.) It is formed
from gelatinous silica, and is deposited in cracks and cavities.
Refractive index = 1-44.
145
IO
