Interesting facts about Opal
- Over 90% of the world’s precious opal comes from Australia and opal is Australia’s national gemstone.
- Precious opal is defined as opaline silica with a play of colour. The term play of colour was created solely to describe opal’s beautiful shifting of spectral hues. Australian opal is referred to as “sedimentary opal” because it is hosted predominantly by sedimentary cretaceous rocks overlaying the Mesozoic Great Artesian Basin. Australian precious opals usually contain around 5-6% water and consists of small silica spheres arranged in a regular pattern. Its hardness of 5.5 to 6.5 on Moh’s scale puts it about half way down the range (roughly the same hardness as glass). It has a specific gravity of 1.9 to 2.3 depending on the amount of water present.
- Black Opal is found mostly around Lightning Ridge, New South Wales.
- Boulder Opals are found through out the vast expanse of the Queensland outback in isolated deposits.
- Matrix Opal is found on most boulder opal fields fifth the best coming from Koriot and Yowah opal fields.
- Pipe Opal is generally found in association with boulder opal deposits.
- Opalised replacements of wood or found and are rarely of gem quality.
- Opals for sale on this site are natural solid Australian opals. With the exception of the Sandstone Matrix Opal (Fairy Opal), this a natural occurring material that has been carbonized and stabilized to enhance the colours (see Types of Australian opal). Sandstone pipe opals have had the sandstone stabilized by the injection of a polymer resin into the sandstone to maintain the integrity of the gem during setting and is mentioned in the text.
- We do not “fracture fill” our opals. If an opal has a flaw it will be mentioned in the text.
95% of Opals on this site are mined by ourselves. The other 5% is from Koriot or Yowah as we love this type of matrix ourselves.