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Onyx is the mystical birthstone for the month of December. 

Onyx is the striped semi-precious variety of Agate with white and black alternating bands. Relatively uncommon in nature, it can be produced artificially through dyeing pale, layered agate. The name comes from the Greek onux, meaning "nail" or "claw", referring to the mineral's color, and it was used by the Romans for a variety of stones including alabaster, chalcedony, and what is now called onyx marble. In its correct usage, the name refers to a (usually) black and white banded variety of Agate, or sometimes a monochromatic agate with dark and light parallel bands (brown and white for example) - but traditionally the name was reserved for black and white banded agate, and brown varieties named Sardonyx.

In recent times the name has become confused with other banded materials, in particular banded calcite formed in cave systems such as the material found in Mexico and Pakistan and often carved, in fact, the majority of carved material (such as book-ends, chess-sets, etc) that are available today are made from this carbonate rock. This is a carbonate material and is not true Onyx. Other names have been used over time for this material, such as "Mexican Onyx" and "onyx-marble". Careless use of these names has resulted in the term 'Onyx' being incorrectly applied to a variety of banded materials that although are beautiful in their own right, are not covered by the original definition of the name.


As with the other chalcedonies, onyx forms through deposition of silica at low-temperatures from silica-rich waters percolating through cracks and fissures in other rocks. (Formula: SiO2)Natural onyx comes from India and South America. Onyx is popular for carved cameos and intaglios because its layers can be cut to show color contrast. 

One story states that Cupid trimmed Venus‘s fingernails with an arrowhead and the Fates turned them to stone so that no part of Her divine body should decay. However, the black-and-white layered variety of chalcedony has acquired a somewhat sinister reputation. In fact, onyx symbolism is replete with connections to bad luck. In Arabic, black onyx is known as el jaza, which means “sadness.” A manuscript from 1875 notes that in China, slaves and menial servants mined onyx. Nobody would willingly touch or own this gem for fear of bad dreams, misfortune, and loss of energy. Although merchants couldn’t sell onyx in China, they brought it west and sold it to the unwary there. (Of course, this profitable trade suggests it wasn’t all that detrimental to business).

Wiser mystics and alchemists knew this reputation resided not so much in the stone itself as in the user’s mind. They had no doubt onyx had depressing qualities. But what did it depress? In 1560, noted mathematician and astrologer Girolamo Cardano wrote that, in India, onyx was used to cool love’s ardor. That’s a form of depression, for sure.

Other writers on gems and mysticism have also noted this purported quality of onyx. Scott Cunningham describes onyx as useful for temporarily dampening the sex drive or containing the energy of any kind. This “energy” could even include a spirit. Onyx stones have long been associated with captured demons or imps. (Almost like a genie trapped in a bottle? Hmmmmm). Cunningham notes that the diamond’s sexy sparkle makes the perfect foil for the depressive onyx. (They look good together, too).

Despite onyx’s negative associations, cultures all over the world have created beautiful jewelry pieces and other objects from this material. For example, the celebrated Amber Room of St. Petersburg, Russia contained mosaics made from marble and onyx. The Ancient Greeks and Romans also carved stunning cameos from onyx as well as sardonyx.