Black Onyx Earring: A Beautiful Gemstone Onyx, the gem's beauty, is a form of chalcedony that occurs naturally with banded parallel layers. Pliny the Elder first recorded it in 77 A.D. and called it after the Greek term for "claw" or "fingernail" owing to its likeness. Some of the intriguing black onyx jewelry has attractive chunks of black onyx, providing the wearer with a fascinating look.