CARNELIAN or CORNELIAN, a variety of chalcedony (q.v.), is most generally of a blood-red colour, though included under this name are specimens of a reddish tint varying in colour from yellow to brown. The colouring matter is probably iron oxide in various stages of hydration, though the particles are so small that only in thin sections under the microscope can they be dis tinguished from the colourless silica in which they are embedded. Though carnelians are recognized in all shades of red, it is con venient to distinguish three varieties; (I) that coloured flesh-red or burnt-brick—the typical carnelian, (2) the honey coloured and (3) that usually called the sard, which is brown by reflected and deep red by transmitted light and was formerly the most valued, because of its greater transparency and depth of colour.
Among the Greeks and Romans the carnelian was one of the most treasured stones and used especially for intaglios of all kinds, examples of which have retained their high polish to a greater extent than many harder stones. The carnelian was also widely used for signets because, as Pliny says (Nat. Hist., xxxvii ; trans. P. Holland, 1634), "it signeth very faire without any of the wax sticking to it." Carnelians are embellished by various processes, notably burn ing and dyeing with salts of iron, and for trade purposes the natural colour is of little importance.
The chief localities are Ratanpur, India; Campo de Maia, Bra zil; Dutch Guiana; Siberia; Warwick, Queensland; Tampa Bay, Fla., U.S.A., and Chesil Bank, South Dorset. (W. A. W.)