Carnelian (also spelled cornelian) is a reddish-brown mineral which is
commonly used as a semi-precious gemstone. Similar to carnelian is sard,
which is generally harder and darker. (The difference is not rigidly
defined, and the two names are often used interchangeably.) Both
carnelian and sard are varieties of the silica mineral chalcedony
colored by impurities of iron oxide. The color can vary greatly,
ranging from pale orange to an intense almost-black coloration.
Carnelian was recovered from Bronze Age Minoan layers at Knossos
on Crete in a form that demonstrated its use in decorative arts;
this use dates to approximately 1800 BC. Carnelian was used widely
during Roman times 2000 years before the present era to make signet
or seal rings for imprinting a seal with wax on correspondence or
other important documents. Hot wax does not stick to Carnelian.
Sard was used for Assyrian cylinder seals, Egyptian and Phoenician
scarabs, and early Greek and Etruscan gems. The Hebrew odem
(translated sardius), the first stone in the High Priest's
breastplate, was a red stone, probably sard but perhaps red jasper.