is a rare variety of precious opal, mainly found at Lightning Ridge, characterised by a spectacular play of spectral colours in a dark body (black, blue, brown or grey); its great depth of colour and large pattern make it particularly prized and valuable.
Opal which is found with a natural black or dark background. This background can range from pitch black to gray giving the stone are darkish appearance when seen from the top. It is the dark background which allows the brilliant colors. Black opal can be any color.
Black opals are a valuable type of precious opals with a dark ground color. They are luminous, iridescent, and frequently have inclusions of many colors ("fire"). Opal is a mineral composed of silica (and some water) and is a species of quartz. The rainbow-like iridescence is caused by tiny crystals of cristobalite. Many opals have a high water content - they can dry out and crack if they are not cared for well (opals should be stored in damp cotton wool). Opals have a hardness of 5.5 to 6.5 and a specific gravity of 1.98-2.50. Black opals are found in Australia.