Opal is divided into two groups, precious opal and common opal. The essential difference between the two is that precious opal has ‘play of colour’ and common opal doesn't. Play of colour is the phenomenon where a rainbow of colours flash across the stone as you move it. This is most likely what you are picturing in your head when you think of an opal. Common opal on the other hand has no rainbow flashes and can have a base colour of white, grey, brown, orange, green, blue or pink. Almost all the worlds precious opal comes from Australia.
Precious opal is divided into three types - black, white and boulder - and is made up of spheres of Silica, the bigger the spheres are the more likely you are to see red flashing in the stone, the smallest spheres will show violet and inbetween sizes will get you blues and greens. If you’re after the highest quality (and most expensive) look for a stone that is showing red flashes.
Black opal is the most expensive and sought after and if you’re looking for a collector’s piece this is where you should be focusing your search, it’s not going to come cheap though with good quality black opals from Lightening Ridge in New South Wales selling for up to $10,000 per carat. Black opal will show dramatic colours on a dark background.
White opal lacks the dark background and so the play of colour can be more delicate. Coober Pedy in South Australia is where most of the best quality white opal is mined. That's the spot where everyone lives underground to escape the baking summer and freezing winter.
Boulder opal is found in Queensland and is a brilliantly coloured thin layer of opal which is usually cut and polished to include the surrounding rock that it forms in. It can have spectacular colours easily rivalling black opal and at a far more accessible price point. Take a look at broken river mining for some stunning examples of ethically mined boulder opal.
Once you’ve fallen in love with opal and decide you need to acquire one, you have three purchasing choices – solid, doublet or triplet. Solid opal, as the name implies, is a solid piece of opal all the way through and is the most hardwearing. It’s also going to require a higher portion of your budget. Next down on the scale we have doublets, which are a slice of precious opal glued to a dark backing stone. And the least expensive option would be a triplet, a very thin slice of opal sandwiched between a dark backing stone and a clear quartz dome. Doublets and triplets are only as good as the glue holding them together and you should definitely avoid getting them wet. There is nothing wrong with purchasing a doublet or triplet as long as the seller discloses the treatment to you and you take the extra care needed to look after your jewellery.
Fancy searching for your own bit of opal rough? Try noodling – yes a real word – which is searching through abandoned piles of mine rubble for bits of opal that may have been missed. You’ll need a fossicking license and then you’re good to go. Happy hunting and lets make some jewellery with your discoveries!
vintage white opals in my stash, most likely from Coober Pedy, South Australia