Crystal Opal

Appearance
The term “crystal opal” refers to any kind of opal (i.e. black opal, white opal, semi-black opal) which has a transparent, translucent, or semi-translucent body. This is also referred to as the “diaphaneity” of a stone. If light is able to pass through the stone, or you can see through an opal, then you are probably looking at a crystal opal. Crystal opals can display any colour of the spectrum in a beautiful play of colour.

However, boulder opals which have a layer of translucent opal are not referred to as crystal opals because of their opaque ironstone backing.

The translucence of a crystal opal often gives it a greater clarity and vibrancy of colour than opaque stones. Pale coloured crystal opals (white crystal opals) are generally more valuable than opaque white opals, and ‘black crystal opals’ can often have more beautiful colour than opaque black opals.

Crystal opals are generally cut in a standard oval shape if possible, however if the nature of the stone dictates, sometimes a freeform or teardrop shape is cut in order to maximise the size and carat weight of the stone. Crystal opals are also cut with a high cabochon if possible as it enhances the appearance of the colour.

Value
Top quality crystal opal may fetch prices of up to AUD $2,500 per carat for a gem quality stone. The clarity and transparency of a crystal opal often enhances the appearance of the colour and therefore gives the stone a higher value than a standard opaque stone.

Record(s)
The world's largest and most valuable gem opal "Olympic Australis" was found in August 1956 at the "Eight Mile" opal field in Coober Pedy. It weighs 17,000 carats (3.4 kg; 7.5 lb) and is 11 inches (280 mm) long, with a height of 4 3⁄4 in (120 mm) and a width of 4 1⁄2 in (110 mm).

Origin
Crystal opals are mined in South Australia and New South Wales, in the same places where black opals and white opals are found. White Cliffs in New South Wales is well known for yielding good quantities of crystal opal.