There 3 types of opal with different values associated to them.
White Opal - light milky opal, comes from the Coober Pedy region in South Australia. It is formed as a seam or in veins throughout the white sandstone. When white opal is cut and polished as a gemstone all the sandstone will be removed from the face of the opal.
Black Opal - highest value - rarest type of opal, comes from the Lightning Ridge area in NSW. Black Opal is also formed as a seam or in veins throughout the white sandstone. When Black opal is cut and polished as a gemstone all the sandstone will be removed from the face of the opal.
Boulder Opal - Is attached to the ironstone host rock naturally and can have the colour of black opal but Boulder Opal is a little more common so will not have as higher value of the Black Opal. Boulder Opal is mined from the central part of Western Queensland.
Crystal Opal - This type of opal can originate from Coober Pedy, Lightning Ridge and also the Queensland Boulder Opal fields. Crystal opal gets its name from the fact that it is crystal clear in appearance when held up to the light and looked through. When crystal opal is worn on the skin (in bigger pieces) or inlayed into a setting, it will display the brilliant colours.
In each of these categories we grade them according to the following guidelines:
Brightness (B1-B5) B5 being the brightest, and B1 being a subdued colour. When you are valuing opal this is one of the most important factors. The brighter the opal the better. When an opal is very bright it stands out from a distance.
Colours, Amount of colours (C1-C7) C7 having 7 colours, C1 as having 1 colour. The more colours an opal has, the better and more valuable. Colours like Red and orange are much rarer than blues and greens and so are valued much higher. The range of colours is endless as opal refracts light and is not a colour itself.
Darkness (N1-N9) N1 being the darkest, darker opal is more attractive and rarer and as such, more valuable.
Size (or carats) Larger the better
Paterns Patterns play an important part of the value of an opal as well. The rarer the pattern, the higher the value. There are many types of patterns such as pin fire, crosshatch, broad flash, Chinese writing, rolling flash, flag harlequin and big blocky patterns such as the famous harlequin pattern.
As you can see opals aren’t opals and they will all be different and unique. It takes decades of studying opals to understand the valuing process and also to have the experience to see many thousands of opals and their associated values.
Talk to us if you need to know more about opals.
Below is an example sheet of body tone and patterns from an article by the Opal Association of Australia.