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very unfrequently larger, and is almost always of a regularly semicircular form,being convex at the top, and flat at the bottom, it is naturally of a smooth and po-lite surface, and is usually worn with its native polish. It has only two colours, a palebrown and a white; the brown seeming naturally the ground, and the white playingabout in it, and seeming deeply sunk in the bottom of the Stone, as the fire colour inthe Opal. This whiteness shifts about in it in the fame manner also as the red in theOpal j and as the Stone is mov’d about in various directions, seems a lucid speck ; or asthe antients have call’d it, a small star moving about to all parts of it: this is the cafewith those which have less of the white in them, but such specimens as have more of it,appear always whiter on one whole side than on the other; and in some lights one mayfee a sort of white line, dividing the Gem as it were into two parts: The brown andwhite are its only natural colours, but is liable, like most other Stones, to some acci-dental tinges; and there are pieces of it met with, which are greenish, blueifh, andyellowish, but they are all the worse for these variegations, never shewing the includedlight so well. It is considerably hard, but greatly less so than the oriental Gems, andwill take a fine polish, though its natural one is so good that it is seldom wrought.

It is found in the East and West Indies, and in Europe : the island of Borneo affordssome very fine ones, but they are usually small; they are very common in New Spain,in the sands of rivers, and in Bohemia are found very frequently immers’d in the famemasses of Jasper with the Opal. Of this I can speak with some degree of certainty,having seen a piece of the Jasper, with a large Asteria and two small Opals bedded in it,and with a cavity, out of which the person who posiess’d it assur’d me, that he hadtaken a large Opal, which he fold for six guineas.

The reader will not expect to find the history of pearls here, they belonging to thethird volume which treats of the animal kingdom. The Turquoise also, tho’ esteem’da native Gem by many, is of two kinds, the one a copper ore, to be seen in its properplace; the other an animal substance, ting’d by cupreous matter, which will therefore befound among the extraneous Fossils.

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