CHRYSOLITE FAMILY.
137. CHRYSOLITE, or PERIDOT, is a soft gem, usually of yellowish green colour, though sometimes it is grass-green, or bluish green, but with a tinge of brown.
It is generally found in fragments and rounded pieces, and rarely crystallized. In the latter case its regular form is an eight, ten, or twelve-sided prism.
Though scarcely harder than glass, and consequently inferior to most other gems in lustre, these stones are not unfrequently used in jewellery, particularly for necklaces and ornaments for the hair; and, when well matched in colour, and properly polished, their effect is very good. They are, however, too soft for ring stones; for, by wearing, they soon become dull on the surface. But it is said that their lustre may, in some degree, be restored by immersing them in olive oil.
To give the greatest brilliancy to this stone, we are informed by Mr. Mawe, that a copper wheel is used, on which a little sulphuric acid, or spirit of vitriol ([24]), is dropped; and that, during the process, an highly suffocating odour is given out. But he is of opinion that the most advantageous way of working it would be that in which glass is cut.
Chrysolite is imported from the Levant, and is said to be found in Upper Egypt, and on the shores of the Red Sea.
BASALT FAMILY.
138. BASALT is a greyish black and coarse grained stone, which is usually found either in globular distinct pieces or in groups of large columns, each of which has from three to eight sides, and is divided horizontally into numerous stones, that very exactly lie upon, or fit into each other.
The most remarkable assemblages of basaltic columns that are known are those called the Giants’ Causeway, on the coast of Antrim, in Ireland, and the Cave of Fingal, in the island of Staffa, one of the Hebrides, or Western Islands of Scotland.
The former, which is believed by the common people to have been an artificial production, the vast labour of giants who formerly inhabited the country, consists of an irregular group of many thousand jointed pillars. Most of these are of considerable height; are in general five-sided, fifteen or sixteen inches in diameter, and each perfectly distinct from top to bottom, though so closely and compactly arranged that it is scarcely possible to introduce any thing betwixt them. This assemblage of columns extends into the sea to a distance unknown, and along a tract of the sea coast of nearly six miles.