Onyx
Onyx is a type of chalcedony, which is itself a form of microcrystalline quartz. Onyxes have straight, nearly parallel bands or layers of colour, which allow skilled gem carvers to cut away material to create cameos and intaglios with extraordinary depth and contrast. Onyxes usually form with very thin layers of colour. Although, very rarely, they can occur in nature with layers thick enough to cut a stone as a solid colour, most solid black onyxes sold today are actually dyed black chalcedonies.
