Black Onyx is a treated chalcedony! Chalcedony is a member of the extensive quartz family and has a density of 6-7 on the Mohs scale. Black onyx is known for its opaque black colour.
Due to its name, black onyx is often confused with "real" onyx. Should a black coloured chalcedony even be allowed to be called onyx? Yes, as long as the word black is put in front of it, it is generally accepted to use the name, and you can assume you are dealing with a treated chalcedony.
Amongst others, chalcedony can be found in Brazil, Madagascar, Uruguay, India, the United States, Great Britain, and Namibia. Chalcedony is related to the zodiac signs Cancer, Sagittarius and Gemini. Read more on which gemstones match which zodiac signs on this page!