Also known as “Milky Opal” it is generally formed in seams in white sandstone, giving it a lighter appearance compared to the black opal. Mined in South Australia in such places as Coober Pedy and Andamooka, the white opal is the most common of all solid opals.
Is opal which forms in cavities of ironstone and is found in Queensland. The opal forms within the cavities of the boulders in both vertical and horizontal cracks. When cut, the ironstone is usually left on the back, giving it a natural dark backing. Because of this dark backing the boulder opal is often dark in nature compared to the white and crystal opal. With boulder opal, you get more of the colours associated with the black opal.
Is dark in colour compared to the lighter opals. People sometimes make the mistake believing that the term “Black Opal” means the stone is completely black. This is not the case. There has to be colour running through the stone for it to be of any value. A Black opal with no colour is of no value. Black Opals are usually mined in Lightning Ridge, New South Wales. They are the hardest and rarest of all the opals to find with the red colour being the most elusive. Black opals will attract the highest prices of all the opals at the highest level.
- Lightning Ridge
Are ironstone concretions resembling ‘nuts’ which contain precious opal in their centre. When you slice or crack the Yowah nut, the precious opal is revealed. These are found in the far South Western mines of Yowah in Queensland.
Are solid opal which have been sliced very thinly and cemented on to a black backing. You can say they are partially man made. The doublet is made to look like the more expensive and rare black opal at a fraction of the price. Doublets do not like water, as over time, this can cause the opal layer to separate
Is similar to the doublet, however is has an extra clear quartz or glass capping over the top of the opal. This protects it and gives it a cabochon, a dome like appearance. Like the doublet, the triplet is made to look like the more expensive and rare black opal at a fraction of the price. Triplets, like doublets, need to be kept out of water.
There are two different types of matrix opal, coming from two different fields. The first is called boulder matrix, which comes from the Queensland fields in the northern part of the opal regions in Australia. This natural boulder opal matrix is untreated and it naturally contains a background of brown Australian ironstone with pockets of opal in it. The other form of matrix opal comes from Andamooka in South Australia. This opal however is treated to give it a darker background. The matrix is soaked in sugar solution and boiled in acid. This causes carbon to deposit in the spaces in the rock, giving it a dark or black opal appearance.