Onyx is a banded variety of chalcedony. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colors of its bands range from white to almost every color. Onyx is formed of bands of chalcedony in alternating colors. It is cryptocrystalline, consisting of fine intergrowths of the silica minerals quartz and moganite. Its bands are parallel to one another, as opposed to the more chaotic banding that often occurs in agates.
Onyx is an ancient gemstone, having been used in jewelry and as an ornamental gemstone for carvings since antiquity. Onyx has traditionally been one of the most important engraving and cameo gemstones, where its most common form was a black base with a white upper layer. Although still used a minor gemstone today, the significance and value of Onyx has been diminished as compared to ancient times.
Rio Kompani offers this kind of Onyx: