Similar to carnelian is a darker and harder stone called 'sard'. The two names are often used interchangeably. Both carnelian and sard are varieties of the silica mineral chalcedony coloured by impurities of iron oxide.
The gemstone has been used since prehistory.
- Websters New World College Dictionary. 4th ed. 2001.
- Duda, Rudolf and Rejl, Lubos 1990. Minerals of the World.
- Tallon F. (ed) Cornaline et pierres précieuses de Sumer à l’Islam. Musée du Louvre, Paris