Queensland Boulder Opal
Queensland Boulder Opal is the name given to opal that has formed inside ironstone boulders of rock. These rocks or boulders are round or of spherical formation and have veins of opal running through them. The opal inside the boulder is not always of good quality but when a good one is found, the colours can be amazing. The colour plays an important part in the value of the opal, patterns also increase the value. As opal is refracting light, the colour in an opal can vary from blue, green, and purple to the more valuable red, orange and yellow.
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Boulder opal is only found in an area through the middle of Queensland Australia It spans from near Cunnamulla to around Winton in the north. See map.
Boulder Opal was first discovered on a sheep station near Quilpie in 1869. Various people took these rocks to the capital cities and then to London. Most opals of the day were milky, so Boulder Opal did not get the recognition it deserved until around 1895. Up until then, people were so impressed by its beauty they thought it must be a fake.
In 1896 the biggest opal rush of Queensland started in the town of Fermoy, now known as Opalton. It was the largest quantity of opal found in any one location throughout Queensland. The Opalton Opal rush lasted for around 6 years between 1896-1901. Unfortunately records are hard to obtain on just how much opal was actually found. Boulder Opal is still being mined from Central Queensland thanks to small family enterprises and individual miners with extreme tenacity. It still remains a highly sought after gemstone.
How does Boulder Opal differ from other types of opal?
The Opal in Queensland has formed in veins of various thicknesses, that run through the ironstone boulders, hence the name Boulder Opal. Other types of Opal occur in seams running through the ground.
As this water then slowly dried out and gelled up, the opal formation began. With a fault present in the ground, friction occurs, creating static electricity. A combination of mineral rich water and a slight electrical charge has grown a crystal structure inside the opal that refracts light and thus produces precious opal. How long this has taken to form is still being debated.
Care of Opals and Opal Jewellery
We cut and polish the Boulder Opal with the opal veneer exposed, leaving the natural ironstone as backing. The combination of the ironstone boulder and the opal within is perfect for jewellery, as we don't necessarily have to set the stones in silver or gold for them to be durable, strong and long lasting.
As a natural gemstone there are no special care instructions. Treat an opal as you would any other gemstone.
Boulder Matrix Opal
Boulder Opal
Are there different types of Boulder Opal?
Every Boulder Opal will be different, but there are two main types:
Boulder Matrix Opal have Opal veins that are running through ironstone rock
Boulder Opal contain thicker opal veins running on top of the rock
How is opal formed?
The opal fields sit on top of the old inland sea that is now the great artesian basin. The ground water in this region is high in minerals and silica that have originated from rotting vegetation in the inland sea. This mineral rich water has then seeped down into gaps and fissures deep underground where the ironstone boulders lay. Sometimes, the silica mixture replaced organic material, such as wood fragments, shells or bone, so that opalised fossils are not uncommon.