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?
Australian black opals are the most valuable and widely known type of opal. Black opal is characterised by a dark body tone which can range from dark grey to jet black. (See the following chart). 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. Some people expect a black opal to be completely black (in which case it would be completely worthless).
Unlike ordinary opals, black opals have carbon and iron oxide trace elements present, which cause the unusual darkness of the stone. Because of their dark body tone, the rainbow colours in a black opal stand out much better than lighter opals.
This vibrancy of colour makes black opal the most valuable form of all opals. 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. 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. This is the principle upon which doublets and triplets are based, which are an imitation of solid black opals.
Black opals are generally cut into an oval shape, however this depends on the natural shape of the stone. Sometimes black opals are cut into freeform or teardrop shapes in order to maximise the size and carat weight of the stone. 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. If the colour bar in an opal is thin, it is impossible to create a domed surface.
Examples of Black Opal
By comparison, black opals are the most valuable form of opal – due to their dark body tone and the resulting vibrant play of colour. Top of the range gem quality black opal can fetch prices up to AUD $15,000 per carat. However, just because an opal is black doesn’t make it valuable. There are many factors including brightness and pattern which determine the overal value of opal. Read more in our article on the value of opal.
Black opals are mostly mined in Lightning Ridge, in northern New South Wales. Lightning Ridge is famous for the black opal and hundreds of millions of dollars worth of black opals have been found there. In 2008, the black opal was named as the ‘gemstone emblem’ for New South Wales. Black opals have also been found at Mintabie in South Australia.