Types Of Opal
PRECIOUS OPALPrecious opal is the valuable form of opal which shows colourful patterns that result from the diffraction of light in a process similar to how the colours of a rainbow are formed. Good quality opals will show some variation in their patterns and colours as they are viewed from different angles, for example when they are turned in the hand, making this precious stone perfect for use in rings and pendants. see more...
Potch, or common opal, is generally of no value compared to precious opal, as it does not show any diffraction of colour. Common opal occurs far more abundantly in the opal mines than precious opals. see more...
Boulder opal is found sparsely distributed over a wide area of Queensland Australia, sandstone or ironstone boulder country where the opal fills cracks and crevices in the ironstone boulders. Opal bearing boulder is always cut including the host ironstone. Boulder opal is in very high demand and extremely precious. Boulder opal is usually cut to the contours of the opal vein creating a baroque wavy surface and is often freeform and irregular in shape, making boulder opal unique and exclusive among it's peers. In boulder opal there is a colour and pattern to suit everyone’s taste, from the brightest flashing red through to electric blues, greens, orange, pink, purple and many more in every shade you could imagine (every colour of the spectrum).
Black opal is the most coveted of all opal varieties and at the high end of the market, fetching unbelievable prices. The "black" in black opal means the gem has a very dark body tone. The most rare colour is red, next is orange, gold and green with blue as the most common colour. A large percentage of black opals come from Queensland Boulder Opal mines in Australia. see more...
Crystal opal is transparent and is pure opal (hydrated silica). It typically has sharp clarity of diffracted colour visible from within and on the surfaces of the opal. When held out of the direct light, crystal opal displays some of the most intense opal colour. This is the type of opal used in opal inlay jewellery, which has the base of the setting blackened before the precision cut crystal opal is set into it.
White opal is the most common type of precious opal with a milky appearance which dominates the diffracted colours. All of the opal fields produce white opal with most of it being mined in Coober Pedy, Australia.
‘Yowah Nuts’ are a sub species of Boulder Opal, they are typically small boulders and are found in a unique formation consisting of a regular band containing nuts packed in a conglomerate. The opal is found either as a central kernel, or as thin veins, surrounding an ironstone centre or traversing the nut, without reaching the outer edge. Yowah is Queensland’s southern most opal field and is centred on the small town of Yowah 40km north east of Eulo and 150km west of Cunnamulla. Koroit is an associated opal field 80 kilometres east of Yowah, Australia.
Once the nuts have been removed from the ground they must be cleaned, sorted and usually sawn, so as not to damage the opal. Yowah Nuts are mostly 1.5 to 3.5 centimetres in diameter, but they may be the size of a fist. The vast majority of these small ironstone concretions are either solid or have hollowed centres and do not contain any opal.
Koroit is located approximately 1000 kilometres from the east coast of Australia, right in the heart of Outback Queensland. The opals from here are unlike opal anywhere else in the world. Koroit renowned for the beautiful and intricate patterns of precious and common opal that run right through the host rocks. Sometimes they are called "Aboriginal Art Opals" due to their resemblance to native Australian paintings. Even some stones with only common opal (potch) can be collector’s pieces, with the patterns in the stone forming beautiful pictures. Picture stones are in high demand worldwide.
The area is also famous for its opal "Nuts". These are ironstone concretions that occasionally contain depos its of precious opal. About one Opal Nut in every ten thousand has a centre of crystal opal. Others have opal embedded into the shell of the Nut, with opal patterns running in concentric circles from the inside to the outside of the Nut. Koroit along with Yowah opal is in great demand worldwide and makes beautiful jewellery or unique collectors pieces. The colours and patterns of Yowah and Koroit are hypnotic. Once you own one opal you will want to own more. see more...
LIGHTNING RIDGE OPALS
Opal is currently being mined from depths between 1 metre (3 feet) and 30 metres (90 feet) below the surf ace. The opal is found in sedimentary rocks that were deposited in a freshwater environment during the Cretaceous period, ab out 110 million years ago. These opal fields may be isolated or occur in groups. The main opal field "groups" are located at Lightning Ridge, Coocoran, Grawin/Carter's, Glengarry/Sheepyard, Wyoming, Jag Hill and Mehi, Australia.
Lightening ridge opal is found as nobbies or in seams with the host rock being shale, thus being uniquely different from boulder opal and Coober Pedy opal, but in saying this all Aust ralian opals have the same chemical and structural
make up only with the host rock being the difference.
COOBER PEDY OPALS
Coober Pedy is a town in northern South Australia, 846 kilometres north of Adelaide on the Stuart Highway. The town is known as the opal capital of the world because of the quantity of precious opals th at are mined there. It is renowned for below ground residences, mostly in refurbished mines, due to the scorching daytime heat. The name 'Coober Pedy' comes from the local Aboriginal term kupa-piti, which means 'whitemans hole' 'waterhole'.
The harsh summer desert temperatures mean that many residents prefer to live in caves bored into the hillsides ("dugouts"). A standard three-bedroom cave home with lounge, kitchen , and bathroom can be excavated out of the rock in the hillside for a similar price to a house on the surface. It remains at a constant temperature, whereas surface living needs air-conditioning, especially during the summer months, when temperatures often exceed 40 degrees Celsius. The opal from Coober Pedy is mainly light or white opal and is largely used in the production of doublets and triplets, with the backing layer enhancing the colours of this light opal.
Opal Triplets are a very thin slice of precious opal glued to a black base of glass, potch or semi precious stone such as tourmaline and covered with a clear natural crystal cap, as the name implies a triplet contains 3 layers.
Opal Doublets are a thin section of either precious, glued to a glass, potch or tourmaline backing, but with no crystal cap to cover the opal, doublets only consisting of the two layers.