Black Opals
fireworks
 ‘The intensity of the colours, the surprising swiftness of their changes and the strangely interesting character of their diverse patterns defies description.’
Tullie Wollaston

Black Opal is the most highly prized of all opals and arguably the rarest of all gemstones.
opalopalopalopal

Compared with the more familiar Light Opal variety, which has a colourless to milky body or background, the black background of Black Opal brightens the range of colours emitted by the stone and heightens their contrast. Thus the ‘play of colour’ is more vivid, the patterns more brilliant and exciting. Something akin to setting off fireworks by night as opposed to by day.

The major source of Black Opal is the area around Lightning Ridge in New South Wales.
However, contrary to popular belief the vast majority of stones found at the ‘Ridge’ are not by definition Black Opal.
In nature there occur many shades of grey between white and black base stones.

opal tone scale opal

More common varieties such as Light, Grey and Semi-Black account for most of the production across the Australian Opal fields. Black Opals constitute less than 5% of all opal production.

‘Red on Black’ is the rarest and most valued of Opals. Purely Red or Multicoloured (displaying 3 or more colours) such scarce stones exceed the per carat price of most other precious gemstones including diamonds.  
opal 
A black back does not make the stone a Black Opal, just as a white or grey back does not preclude it from being a Black Opal.

Although Black opals are synonymous with Lightning Ridge and have been found on numerous fields around the town, dark and black stones have occasionally been found elsewhere on the Australian Opal fields.

In South Australia for example Black Opal has been found at Coober Pedy’s ‘Black Flag’ field, also Mintabie yielded considerable quantities of stable Semi Black Opal and Andamooka has produced Smokey Jelly Opal.
opal
Native to Queensland, Boulder Opal comes in 3 base colours; white, brown and black.
Most Boulder Opals have ironstone showing on the face as inclusions or the brown ironstone backing is visible through the clear Opal top, but a very small percentage of Queensland Opal can be classified as Black Boulder Opal.

Black Boulder Opal has a thin layer of black potch between the Opal and the ironstone matrix, with no visible ironstone in the face of the stone, making it indistinguishable from Black Opal apart from its natural ironstone backing.