Carnelian

Carnelian is a variety of chalcedony, silica made of tiny crystals, colored orange, red or reddish brown by iron oxides. Its darker, harder cousin is called sard.

It is one of the oldest stones in jewelry making. The Indus Valley Civilization made etched carnelian beads as early as the 3rd millennium BCE, and the Egyptians, Assyrians and Greeks valued it highly. The Romans liked to carve it into seals for signet rings, because hot wax does not stick to carnelian. A stone with serious office skills.

The name comes from the Medieval Latin corneolus, after the cornel cherry, whose translucent red looks similar. The spelling carnelian is a 16th-century corruption of the older cornelian.

Worth knowing: much of what is sold as carnelian is actually ordinary agate that has been heated or stained. Heating turns the iron impurities in the stone a bright orange-red. That doesn't make the stone fake, but it does make it less natural than it looks.

Known sources include Peru and Sri Lanka, with other deposits in Indonesia, Brazil, India, Iran, Siberia and Germany. With a hardness of about 7 on the Mohs scale, it takes a good polish and is used for beads, tumbled stones and carvings.