Translucent, semiprecious variety of the silica mineral chalcedony that owes its red to reddish brown colour to the incorporation of small amounts of iron oxide. A closely related variety of chalcedony, sard, differs only in the shade of red. Carnelian was highly valued and used in rings and signets by the Greeks and Romans, some of whose intaglios have retained their high polish better than those made from harder stones. Carnelian is mined principally in India, Brazil, and Australia. Its physical properties are those of quartz.