CARNELIAN  , a red variety of

chalcedony, much used as an ornamental stone, especially for seals . The old name was cornelian, said to have been given in reference either to the horny appearance of the stone (Lat. cornu, " horn ") or to its resemblance in colour to the berry of the cornel; but the original word was corrupted to carnelian, probably in allusion to its reddish colour (carneus, " flesh-coloured ") . Some carnelian, however, is brown, yellow or even white . Certain kinds of brown and bright red chalcedony, much resembling carnelian, pass under the name of sard (q.v.) . The Hebrew odem was probably a red stone, either carnelian, sard or jasper . All carnelian is translucent and is thus distinguished from jasper of similar colour, which is always opaque . The red colour of typical carnelian is due to the presence of ferric oxide . This is often developed artificially by exposure to sunshine, or to artificial heat, whereby any ferric hydrate in the stone becomes more or less dehydrated; or the stone is treated with a solution of an iron salt, like ferrous sulphate, and then heated, when ferric oxide is formed in the pores of the stone . An opaque white surface is sometimes produced artificially on a red carnelian: this is said to be done by coating the stone with carbonate of soda and then placing it on a red-hot iron; or by using a mixture of potash, white lead and certain vegetable juices, and heating it on charcoal . Inscriptions and figures in white on red carnelian (" burnt carnelian ") are well known from the East . Much carnelian comes from India, being mostly derived from agate-gravels, resulting from the disintegration of the Deccan traps, in the neighbourhood of Ratanpur, near Broach . A good deal of the carnelian now sold, however, is Brazilian agate, artificially stained .