Onyx

History and lore

The Greek onyx means "fingernail" or "claw", a name usually explained by the pale, curved band of some stones, like the half-moon at the base of a nail. Modern books often repeat a tale in which Eros trimmed the sleeping Aphrodite's nails and the gods turned the parings to stone, but an ancient source for that story is hard to find and it is probably later embroidery.

For Greek and Roman craftsmen, onyx meant chalcedony in straight, contrasting layers. A carver could cut through a white layer to leave a figure standing in relief on a dark ground, and onyx became the classic material of cameos, of which the first-century CE Gemma Augustea in Vienna, a two-layered onyx carved with the emperor Augustus among the gods, is among the most celebrated. Pliny the Elder notes that Arabian craftsmen boiled stones in honey to improve their colour, an early form of the technique still used to make black onyx.

In the traditions

In Exodus 28:9–12, two shoham stones were set on the shoulders of the High Priest's ephod, each engraved with the names of six of the twelve tribes of Israel; the King James Bible calls them onyx. Onyx is also the eleventh stone of the breastplate itself: "a beryl, and an onyx, and a jasper" (Exodus 28:20). Genesis 2:12 places "bdellium and the onyx stone" in the land of Havilah. As with other breastplate stones, the identification is debated: ancient translations render shoham in different ways, and carnelian, beryl and malachite have all been proposed. Revelation 21:20 names sardonyx, onyx layered with red sard, as the fifth foundation of the heavenly city.

Medieval lapidaries gave onyx a sombre reputation: worn at the neck it was said to bring melancholy, troubled dreams and quarrels, and Kunz notes that an Arabic name for it was associated with sadness. Renaissance magic followed the same line; Agrippa lists onyx first among the stones of Saturn, the planet of gravity and restraint. Victorian mourning jewellery used black onyx alongside jet. Some older month lists give onyx to July; modern lists prefer sardonyx for August.

Meaning and symbolism

Onyx stands for polarity, with black and white held together in one stone, and for steadiness, self-control and the serious virtues of Saturn. Because seals and signet rings were often cut in it, it also carries associations of identity, oath and authority, a meaning that echoes the names of the tribes engraved on the ephod. Modern crystal books describe it as protective and grounding; these are recent ideas, and scientific studies have not found that stones change mood or fortune.

The mineral

Onyx is chalcedony, a compact form of quartz made of microscopic fibres, distinguished from agate by its straight rather than curved banding, and from sardonyx by the absence of red-brown sard layers. Naturally uniform black chalcedony is very rare. Almost all black onyx on the market is grey chalcedony soaked in a sugar solution and then treated with acid, which carbonises the sugar in the stone's pores; the method has been practised industrially at Idar-Oberstein in Germany since the nineteenth century and gives a stable colour. Sources include Brazil, Uruguay, India and Madagascar.

Hardness is 6.5–7 and the stone is tough and takes a high polish. "Onyx marble" or "Mexican onyx" is a different material altogether: banded calcite or aragonite, much softer (about 3), easily scratched with a knife. Black glass, the commonest imitation, is warmer to the touch and may show bubbles. Clean onyx with warm soapy water and a soft cloth.

Sources and further reading

• Genesis 2; Exodus 28; Revelation 21 — King James Bible, 1611
• Natural History, Book 37 — Pliny the Elder, c. 77 CE
• De lapidibus — Marbode of Rennes, c. 1090
• Three Books of Occult Philosophy — Heinrich Cornelius Agrippa, 1533
• The Curious Lore of Precious Stones — George Frederick Kunz, 1913
• Gems: Their Sources, Descriptions and Identification (6th ed.) — Michael O'Donoghue (ed.), 2006