Onyx is an onyx gemstone, typically consisting of two contrasting layers of nearly black and shiny white chalcedony in alternating bands, which are usually parallel to each other. Figural forms are also onyx, with their color stemming from the same crystal structure as agate.
There is a pronounced fibrous structure in onyx, which causes the parallel bands to appear to be striated or ribbed and this same structure, coupled with gem-quality onyx’s ability to take an excellent polish, has caused it to be used as an imitation of jade. Agate and onyx are both cryptocrystalline forms of silica, and silicon dioxide (SiO). The two stones do not have the same components in pure form; however, all quartz is a form of silica.
Onyx is the name for chalcedony with internal bands of black and white. It is the skeleton of this gem, although it can be streaky. The name comes from the Persian word for “astragalus”, or turtle. Onyx is found in Brazil, Madagascar, Sri Lanka, Myanmar (Burma), Afghanistan, Iran, and Nepal. All forms of chalcedony are known as onyx.
Onyx was used to make beads and jewelry from prehistoric times to almost the ancient Roman period in Europe and the Middle East. It was also used by the Ancient Egyptians and Chinese. They believed it would prevent harm if one were to carry the stone.
The Romans used onyx to create seals because it was also related to trust in business dealings. Before the 1980s, gemologists used a method of identifying onyx that involved using a burner and sulfuric acid, causing the sample to quickly blacken and burn. However, it was later determined that this test was due to impurities in the sample and not an indication of true onyx. Gemologists currently use a wet test for identifying the stone. It is done by lightly scraping the surface of the sample with a sharp instrument, then placing it in water. If it is onyx, the pattern will remain visible underwater.
Recently, synthetic onyx has been used to make paving slabs, which are popular in some areas of the world.
In the U.S., historically the state of New York was the primary source of onyx. In recent years, however, Arizona and Texas have become larger production centers for onyx. This is due primarily to a small number of manufacturers who specialize in producing various grades of synthetic onyx for commercial use. The synthetic form of onyx is often used more than natural onyx for inlay work, where it is popular because of its uniform color and texture.
The onyx group has found increasing use as a gemstone, with commercial quantities mined only from Brazil and Uruguay.
There are also two main types of onyx: “black” (dark brown to black) and “white” (light to dark brown). Black Onyx is the most common, and the most affordable. White Onyx can last for thousands of years. Onyx is mined in Brazil, Uruguay, and Argentina. It can also be found in the USA, Canada, Mexico, Pakistan, and Greece. Black Onyx was used as a material for small sculptures in Precolumbian Mesoamerica. It is found in the states of Chihuahua, Coahuila, and Durango in Mexico, Eureka County, Nevada, New Mexico, and Arizona.
Blue Onyx is a rare form of onyx. It contains a high amount of boron and chromium present in the mineral structure. A saturation grading system was established for this material to improve its physical properties. The shape of the blue Onyx is also very unusual. The cutting into various shapes from flat disks to other shapes gives this material a distinctive look.