Onyx is a striped, semiprecious variety of agate, with white, black, brown or red alternating bands. It is different from regular agate only in that the bands of which it is composed are parallel and regular. The name onyx originates from the Greek word onyx for "fingernail" or "hoof," probably because of its weak transparency or possibly its color. Onyx may chip or scratch rather easily, so store it carefully.
Nearly all black onyx on the market has been rendered a uniform, permanent black color with a treatment using sugar and acid (and/or heat). This process has been used on the gemstone for thousands of years and is water safe.
Onyx is one of the 12 stones mentioned in the Bible as adorning the breastplate of the high priests, and is also mentioned in Genesis 2:11,12: "... the gold of that land is good; there is bdellium and the onyx stone." The ancient Greeks and Romans used onyx for cameos and intaglios, and in India, onyx was worn for protecting against the evil eye and also for cooling ardor (it was believed that onyx provoked discord and separated lovers). In the Middle East, onyx was used as a worry stone because people believed the gemstone absorbed negative energy - a belief that may have been produced by the Chinese miners who feared it and pulled the material out of the mine to immediately sell outside the country.
Onyx is purported to help eliminate apathy, stress and neurological disorders, eliminate negative thinking, and sharpen the wits of the wearer. It is used to change habits, in addition to helping concentration levels and aiding absentmindedness. Some think it makes the wearer more eloquent, and thus it is worn for public speaking. The main sources of onyx are India and South America, but it is also found in China, Madagascar, Mexico and the U.S.A.