in the natural history of the ancients, the name of a black marble, called also the lapis obsidianus. It is very hard, and of a fine black; and, beside the many uses which the ancients put it to, is well known among our goldsmiths by the name of the touchstone; most of them being furnished with nothing better for this purpose than a piece of this: though the basaltes, which might be had plentifully enough, is greatly preferable for those uses; any black marble, however, that is tolerably hard, will do. There is a very fine and elegantly smooth marble, of a compact texture, and fine glossy black, but showing no glittering particles when fresh broken, as most of the black marbles do. It is extremely hard, and cuts with difficulty, but is capable of the highest polish of any marble. The ancients had it from Ethiopia and the island of Chios; we have it from Italy.