1911 Encyclopædia Britannica/Carnelian

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. (See Agate.)