Opal Stones - 4 major types of opal
Opals are classified into two types, “Light” and “Dark”. This categorization is based on the body colour of the opal.
Light Opal (White Opal)
Commonly referred “White Opal', it can be identified by a light body tone. White Opal is not quite rare as the black varieties.
Milky White Opal – this is the most common type of opal, and is translucent with a creamy appearance which dominates the diffracted colours.
Regular White Opal – the base colour ranges from whitish to yellow. The diffracted colours are brighter than in milky opal and often the stone has a degree of transparency.
Grey Opal – This is almost always opaque to translucent ranging from light grey colour. Opal darker than it classed as black opal.
Opal of any body colour will be opaque, translucent or transparent. When an opal is transparent or very translucent and the clarity of colour is sharp it is called a “Crystal Opal”.
This variety includes opal which is transparent or very translucent and in better qualities show a distinct and very bright range of colours. Light Crystal Opal generally comes from South Australia.
Black Crystal Opal is found in the Lightning Ridge fields, this type has a smoky colouring, which the Light Crystal Opal does not have.
Dark Opal (Black Opal)
Black opal could best be described as opal with a dark (dark grey to jet black) background colour. When you view from above, you can see a black backing (called potch) on the bottom of opal. It can be crystal or opaque. The face of the stone predominantly radiates hues of red, blue, green, and orange.
“Boulder Opal” is formed naturally in an ironstone rock (boulder). Boulder opal is found in select areas of inland Queensland.
Solid boulder opals have the top surface almost entirely covered with precious Opal. The most expensive Boulder Opals are those with a dark body colour (black) and a full face of precious opal with a regular surface and the brilliance of colour is the most important factor.
Boulder Matrix Opal
Boulder “matrix” opal is a peculiar opal formation where flecks of rich, flashing colours of opal are scattered throughout the brown ironstone. This opal is mostly found in fields in far south western Queensland. Unlike regular Boulder Opal the host rock is part of the visual attraction of the stone, the blend of the opal and rock creates unique patterning, colour, and texture.
Yellow, Orange and Redish colour opal called Fire Opal is mined mainly in Queretaro in Mexico.
Doublets & Triplets
Doublets and triplets are combination of natural opals and artificial veneers. A doublet opal is a layer of precious light opal bonded to a black backing, simulating black opal. A triplet opal is a thin veneer of precious light opal bonded to a black backing with a protective crystal dome glued to the top. Triplets traditionally use a lower grade of opal than doublets.