CHALCEDONY, in mineralogy, a spe cies of the flint genus ; of which there are, according to Werner, two subspecies, viz. the common chalcedony and the came Ilan : the colour of the former is grey in all its shades. It is commonly semi-trans parent, harder than flint, brittle, diffi cultly frangible ; and the specific gravity, according to Kirwan, is about 2.6. Infu sible before the blow-pipe. It is found mostly in balls, in amygdaloid, also in angular pieces and veins, in porphyry and amygdaloid. The cubic variety occurs in Transylvania, and the other varieties in Iceland, the Feroe Islands, Silecia, Sax ony, Siberia, Cornwall, Scotland, &c. It is susceptible of a fine polish, and is em ployed as an article of jewelry. It de rives its name from Chalcedon, in Asia, where it was first found. Onyx is con sidered as the most valuable variety of this species, and, on account of its be ing capable of receiving a high polish, is very much prized. It is principally cut in bas relief work, and the finest specimens for that purpose are brought ,from the East Indies. The dendruic
variety is named mocha stone, being brought, originally, as was supposed, from Mocha, on the Red Sea ; but it is now generally understood that the word mocha is a corruption from the German word mocks, which signifies moss; and it is affirmed that no stone of the kind is found near Mocha.
The principal colour of the carnelian is blood red, of all degrees of intensity ; from this it passes into milk-white, and also into a kind of yellow. Semi-transpa rent ; and in many other of its characters it agrees with the common chalcedony. It is found accompanying agate, and, in general, has the same geognostic situa tion as chalcedony. The fine oriental va rieties occur in rolled pieces. The most beautiful carnelian is brought from Arabia and Ilindostan ; it is also found in different parts of Europe, and is used for seals, bracelets, crosses, and other or naments.