Rocktober / Black Onyx

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.