The majority of carved items sold as 'onyx' today are this carbonate material. This material is much softer than true onyx, and much more readily available. The name has also commonly been used to label other banded materials, such as banded calcite found in Mexico, India, and other places, and often carved, polished and sold. Most 'black onyx' on the market is artificially colored. Artificial treatments have been used since ancient times to produce both the black color in 'black onyx' and the reds and yellows in sardonyx. Black onyx is perhaps the most famous variety, but is not as common as onyx with colored bands.

Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. Its bands are parallel to one another, as opposed to the more chaotic banding that often occurs in agates. It is cryptocrystalline, consisting of fine intergrowths of the silica minerals quartz and moganite. Onyx is formed of bands of chalcedony in alternating colors. Onyx, as a descriptive term, has also been applied to parallel banded varieties of alabaster, marble, obsidian and opal, and misleadingly to materials with contorted banding, such as 'Cave Onyx' and 'Mexican Onyx'. Commonly, specimens of onyx contain bands of black and/or white. The colors of its bands range from black to almost every color. 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. Onyx primarily refers to the parallel banded variety of the silicate mineral chalcedony.

For the 1984 video game, see The Black Onyx.

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