BLACK ONYX SILVARIA COFFIN NECKLACE

Nearly all Black Onyx is chalcedony treated to an even black. The color is stable in normal wear, but avoid long soaking, harsh chemicals, and ultrasonic or steam cleaning. Not for elixirs or ingestion.

Onyx has been cut, carved and worn since antiquity, and the solid black form became the jeweler's standard once stonecutters learned to darken pale chalcedony evenly. Most of the rough worked today comes from the agate fields of Brazil and Uruguay, with further supply from India.

Black Onyx is chalcedony, a microcrystalline variety of quartz (silicon dioxide). In strict gemological terms onyx is chalcedony with straight parallel bands, classically black and white. Naturally solid black chalcedony is uncommon, so nearly all Black Onyx on the market is gray chalcedony or agate permanently darkened by a sugar-and-acid or heat treatment, a practice with roots in antiquity that became standard in the gem trade in the 19th century.

• The Greeks named the stone onyx, their word for a fingernail or claw. In one telling, Cupid trimmed the nails of the sleeping Venus and the clippings, too divine to perish, turned to stone where they fell.
• Old lore holds that onyx keeps the memory of whatever happens to the person wearing it, which made it a stone of secrets and a favorite for psychometry, the reading of an object's history by touch.
• Tradition said that onyx worn at the neck cooled desire and encouraged restraint, an early version of its lasting reputation as the stone of self-control.