Both these kinds are highly esteemed by lapidaries, for the formation of vases, snuff boxes, and trinkets of various kinds. Of sardonyx the ancients made those beautiful cameos, many of which still ornament our cabinets. The ingenuity they have shown, in the accommodation of the natural veins and marks of the stone to the figures engraven upon them, is such as to excite, in many instances, the greatest admiration.
It is said that we are entirely ignorant of the country whence the ancient artists obtained the large specimens of sardonyx which are now found in some cabinets.
Onyx is imported from the East Indies, Siberia, Germany, and Portugal.
93. CARNELIAN is another kind of calcedony usually of a red or flesh colour, though sometimes white, orange, or yellow.
On several of the British shores carnelians are found with other pebbles: but the most beautiful and valuable kinds are imported from the East Indies. These are sometimes so large as to measure nearly three inches in diameter. The kinds principally in request are those of pure white, and bright red colour; and jewellers have the art of changing the colour of the yellow varieties to red, by heat.
No stone is so much in request for seals as carnelian. It is likewise cut into beads for necklaces, and stones for ear-rings; into crosses, bracelets, and other trinkets, which, in India, form a considerable branch of traffic. The amount of the sale value of different kinds of carnelian goods vended by the East India Company in 1807, was 11,187l.: but, in other years, it has not usually been so much as half that sum.
Formerly carnelians were exported from Japan to Holland; and thence were carried to Oberstein, in France, to be exchanged for the agates of that country, which were exported to China.
The carnelian was much esteemed by the ancients; and many fine engraved carnelians are preserved in different collections.
94. CHRYSOPRASE, an extremely hard kind of stone, of clear and delicate apple-green colour, is considered to be a kind of calcedony.
This beautiful mineral has hitherto been found only in the vicinity of Kosemitz, and in a few other parts of Lower Silesia. It is susceptible of a high polish, and is much prized by jewellers when its colour is deep and pure. Its colour, however, is so fugitive, that, if kept in a warm and dry situation, it loses the greatest part of it; and if exposed to moisture it becomes much altered. Lapidaries assert, that great care ought to be taken in the polishing of it;—pretending that if, from want of sufficient moisture, or by the too rapid motion of the wheel, it be over-heated, it will become whitish or turbid.