ROCK-CRYSTAL.
Shwin-tsing, Shwi, CHIN. Koreh, . . . . Shih-ying, . . . „ Balur, HIND.
Rock-crystal is the common name for the trans parent crystals of quartz, of which it is the purest form, being composed of 99.34 per cent. of silica, with a trace of alumina. The crystal alluded to in Genesis xxxi. 40 as frost, and in Job vi. 16 as ice, and the Persian word Balur, seem to be applied indifferently to ice and rock-crystal. Rock-crystal occurs abundantly in many parts of India, and that of the south of the Peninsula is known as Vellum stone, from the place of its occurrence. Near Tanjore the mines are of great value, and the stone is cut into a great variety of ornamental objects.
The districts in British India richest in quartzose minerals are those of Dowlatabad, along the banks of the Seena river, and the neighbourhood of Rajpipla. It is found at Madagoolah.
The village of Aurangpur is situated in a small valley surrounded by hills, and the roads leading to it from all sides are, for a distance of three miles at least frorn the village, impassable to any but foot passengers and cattle, from their rocky and precipitous character. Its mines of rock crystal are situated about two or three miles to the south-west of the village, and can only be approached by paths like those just described.
The deposit of crystal occurs in a small valley or basin among these hills, about two or three miles to the south-west of the village of Aurangpur. The valley is about 500 yards long and from 50 to 100 yards broad, and dips towards the north. The only part of the deposit which has been worked is the south end. If made red-hot, and plunged re peatedly into the tincture of cochineal, it assumes a ruby colour ; if into a tincture of r6d sandal, it takes a deep red tint ; into tincture of saffron or a tincture of turnesol, a yellow like the topaz ; into juice of nerprum, it takes a deep violet like the amethyst ; and into a mixture of tincture of turnesol and saffron, it becomes an imitation of the emerald. Steeping the crystal in oil of turpentine saturated with verdigris or spirits of wine, holding dragon's blood or other coloured resins in solution, depth of tints are produced proportioned to the time of steeping. Crystals can be coloured if heated in a, crucible with orpiment and arsenic. Crystal coloured red, as false rubies, are known in France as rubaces.— King, p. 178. See Precious Stones.