Sard

Sard is a reddish-brown chalcedony, SiO₂, much used by the ancients as a gemstone. Pliny the Elder states that it was named from Sardis, in Lydia, where it was first discovered; but the name probably came with the stone from Persia (Pers. sered, yellowish-red). 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 carnelian or red jasper. Some kinds of sard closely resemble carnelian, but are usually rather harder and tougher, with a duller and more hackly fracture. Mineralogically the two stones pass into each other, and indeed they have often been regarded as identical, both being chalcedonic silica colored with iron oxide. The range of colors in sard is very great, some stones being orange-red, or hyacinthine, and others even golden, while some present so dark a brown color as to appear almost black by reflected light. The hyacinthine sard, resembling certain garnets, was the most valued variety among the ancients for cameos and intaglios. Dark-brown sard is sometimes called sardoine, or sardine, while certain sards of yellowish color were at one time known to collectors of engraved gems as beryl.

References

*1911
*http://www.mindat.org/min-7607.html