Sard

Sard is the uniformly colored red-brown or brownish-yellow variety of Chalcedony, which in turn is a microcrystalline variety of Quartz.

There is no strict separation between sard and cornelian/carnelian (red to reddish brown), because they are both chalcedonies found in the same deposits and were employed for the same objects.

The tints of a sard stone may be reddish or orange. Good-quality material is blood-red when light is passed through it, and blackish red in reflected light. The distinction between sard and cornelian is a matter of individual judgment, and one is taken for the other, but usually sard is a bit darker than cornelian. The colour of sard and cornelian is caused by the dispersion of very tiny particles of hematite, one kind of iron oxide.