Onyx is chalcedony at midnight: dense, even black that takes a superb polish — the graphic backbone of signet rings, beads and Art Deco design. Hardness about 7 keeps it crisp in daily wear.Our onyx is natural chalcedony, certified by GEMIC Institute’s laboratory in Siem Reap and photographed piece by piece. Each stone is unique; tracked worldwide delivery and a 30-day return period.