If the colour bar in an opal is thin, it is impossible to create a domed surface. Black opals are normally cut with a low cabochon, due to the opal colour bar often being much thinner in black opal than in white or crystal opals. Sometimes black opals are cut into freeform or teardrop shapes in order to maximise the size and carat weight of the stone. This is the principle upon which doublets and triplets are based, which are an imitation of solid black opals.īlack opals are generally cut into an oval shape, however this depends on the natural shape of the stone. The darker this potch backing is, the darker the body tone, which usually makes for greater vibrancy of colour and a higher value black opal. Often a black opal will have a natural layer of potch (colourless opal) left on the back of the stone, which can give the stone an extra darkness and vibrancy of colour. This vibrancy of colour makes black opal the most valuable form of all opals. Because of their dark body tone, the rainbow colours in a black opal stand out much better than lighter opals. Unlike ordinary opals, black opals have carbon and iron oxide trace elements present, which cause the unusual darkness of the stone. Some people expect a black opal to be completely black (in which case it would be completely worthless). However this refers only to the general body tone of the stone, and is not related to the rainbow or spectral colours present in the opal. Black opal is characterised by a dark body tone which can range from dark grey to jet black. FAQ: What is a black opal? What colour are black opals? Where are black opals mined? What makes a black opal black? What is a semi-black opal? How are black opals valued? How much is a black opal worth? AppearanceĪustralian black opals are the most valuable and widely known type of opal.

Often opal