What is an Opal?
Opal is one of the world’s most beautiful and precious gemstones. Australia is one of the main producers and is Australia’s National Gemstones.
Opal is as old as the dinosaurs, it was formed over 80 million years ago when parts of Australia was covered by an inland sea.
Opal got its name from the latin word “Opalus” which means “Change in colour”. They were first used by the romans 2000 years ago. The opals they used came from the mountain regions of Slovakia in Europe and were light in colour.
They have all the colours of the rainbow and a play of colour that no other stone has. It is a 100% natural stone.
The definition of the opal is “Non crystallised minerals made by silicon dioxide combined with water”. Opal itself is made from the same mineral “silica gel”, but the comparison to these opals, is one that takes more than 6 million years to form and silica gel and the other takes few hours to make in factory by a human.
How are they formed?
Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids, caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed.
What are the opal patterns?
Pattern refers to overall character and look of the stone. Lightning Ridge black opal displays a wide variety of patterns which contribute to its beauty and value. The broader and more distinct patterns such as straw, ribbon and harlequin occur rarely and are highly prized. Smaller patterns such as floral and pinfire are more common. Many boulder opals are called picture stones as they often mirror elements of nature. White opal usually exhibits smaller pattern.
How are they mined?
The mining technique varies for different types of opal, black and light is generally mined through a shaft and tunnel system. Boulder is mostly mined by open cut method.
Black Opal – Mining is mostly done by drilling a shaft approx. 1 meter in diameter down to a depth of 15-20 meters approximately. When the clay level is reached a horizontal tunnel is then dug out in different directions to look for opals. If opals is found a larger area will be dug out sometime with timber support for the roof not to cave in.
The ‘Opal dirt” is mined and brought to the surface using several types of equipment like an underground digger, bogger, blower or automatic hoist. After it gets to the surface, it will be taken by tip truck to a dam where it will be washed using a cement mixer with water. After the clay has dissolved any opals can be picked in the tilings. The rough stones will then be brought to a cutter to be cut.
Boulder Opal – Mining process is different from black opal. First stage is using a prospecting drill to find opal.
An open cut is done using an excavator and bulldozer to get to the opal level to find the boulders.
Manual labour is then used to check boulders up closer for opal. The next step, is to retrieve the boulder from the ground. The Opal veins contained rock is taking back to the camp to be cut through using 17-inch diamond saw. We then assess the contents, and it then follows the similar cutting process as per black opal.
Before buying, determine whether you are looking at a doublet, a triplet, or a solid opal. Doublets & triplets consist of a very thin slice of opal, cemented onto a black backing. This causes the stone to be dark & bright in colour (the idea being to replicate the highly valuable black opal). The advantage of buying a doublet or triplet is a lower price (they are much cheaper to produce) – however the disadvantage is they may eventually be destroyed if repeatedly immersed in water.
Solid opals are therefore considered much better – they’re 100% the “real thing” and are a quality, long-term investment.