Opal
A close look at October’s traditional birthstone: what it is, where the best of it comes from, and how to choose one well.
Opal is the one gem that won’t sit still. Tilt it and the colours shift, flare and vanish, and no two stones do it the same way. It’s October’s traditional birthstone and very much our own: Australia produces around 95 per cent of the world’s gem opal, and in 1993 it was proclaimed the national gemstone. It’s also softer than most gems, which is worth knowing up front. Here’s what’s worth knowing before you fall for one.
What is an opal, really?
Not a crystal at all
Most gems are crystals. Opal isn’t. It formed when water carrying dissolved silica seeped into cracks in the rock and slowly dried out, leaving the silica behind, and it still holds a little of that water today. Where the silica settled into tiny spheres of the same size, stacked in neat rows like ping-pong balls in a box, light passing through is split into its colours. That’s the flash of red, green and blue that moves as you turn the stone, known as play-of-colour. Where the spheres are jumbled, there’s no flash at all. Miners call that potch. Same material, very different stone.
Reading the colour
The background first, then the flash
Every opal has two layers of colour. There’s the body tone, the background the colours play across, which runs from jet black through to milky white or clear as glass. Then there’s the play-of-colour itself: how bright it is, which colours show, and the pattern they make. A darker body makes the flashes look more vivid, which is why black opal sits at the top of the market. Red is the rarest flash, because it takes the largest spheres to make it. An opal that shows strong red from several angles is one to take seriously.
Where the finest are found
About as local as a gemstone gets
Around 95 per cent of the world’s gem opal comes from Australia, from fields strung around the edges of the Great Artesian Basin, the bed of an ancient inland sea. Each field has its own character. Lightning Ridge in New South Wales is famous for black opal. Coober Pedy and Andamooka in South Australia turn out light and crystal opal. Out in Queensland, from Winton down to Yowah, the colour runs through dark ironstone as boulder opal.
Five places worth knowing
The Virgin Rainbow
Opal that grew inside a fossil
In 2003, veteran miner John Dunstan was digging through the old workings of a Coober Pedy mine when he turned up something about the length of a finger. Cleaned up, it proved to be a belemnite, an extinct squid-like creature from that inland sea, with its skeleton replaced entirely by opal. The Virgin Rainbow now belongs to the South Australian Museum in Adelaide and is often called the finest opal ever found.
A stone with meaning
Hope, purity, truth
For centuries opal was a stone of hope, purity and truth, and some believed it carried the powers of every coloured gem at once. In some Aboriginal stories it was made when the colours of a rainbow touched the earth. Opal was named October’s birthstone on the first official list in 1912, and it’s the traditional gift for a fourteenth wedding anniversary.
What to look for
Choosing an opal well
Play-of-colour is where most people start with opal. Look at how bright the colour is, how much of the stone it covers, the range of colours you can see and what happens as you move the stone.
Then look at the body tone, along with the stone’s transparency, inclusions and surface. Cut still matters, but not because an opal needs to fit a standard shape.
Finally, know how the opal is constructed. A solid opal is a single piece rather than an assembled stone. A doublet uses a thin layer of opal bonded to a backing, while a triplet adds a clear protective layer over the opal as well.
Play-of-colour
Look at brightness, range of colour and how much colour you see as the stone moves.
Pattern
The way the flashes and patches of colour are arranged across the stone.
Body tone & clarity
Consider the background colour, transparency and any inclusions or surface features.
Construction
Know whether you’re looking at a solid opal, doublet or triplet.
With opal, the stone in front of you matters more than ticking off a standard set of four Cs.
Can you wear opal every day?
Yes, but where you wear it matters.
Opal can absolutely be worn regularly, but it needs a little more care than many other gemstones. It is softer and more vulnerable to scratching, chipping and sudden changes in temperature, so the type of jewellery makes a difference.
Earrings and pendants are generally easier places to wear opal because they are less exposed to everyday knocks. Rings take more wear, so protective settings and a little more awareness go a long way.
Earrings & pendants
These pieces are less likely to be knocked against hard surfaces, making them an easier way to enjoy opal regularly.
Rings
Rings are exposed to more impact and abrasion. A protective setting helps, but opal still needs more care than a harder everyday gemstone.
Opal isn’t too delicate to wear. It just isn’t a gemstone to treat carelessly.
Caring for yours
A gentler touch
Opal sits around 5.5 to 6.5 on the Mohs scale, so it needs a little more care than many gemstones used in everyday jewellery. It also contains water, which means heat and sudden changes in temperature are best avoided.
Clean it gently
Use warm soapy water and a soft cloth. Avoid ultrasonic and steam cleaners.
Avoid extreme heat
Long periods of strong heat or sudden temperature changes can be hard on opal.
Know if it’s assembled
Doublets and triplets are best wiped clean rather than soaked, as water can work into the bond between the layers.
Store it separately
Keep opal away from harder gemstones that could scratch it, and have ring settings checked from time to time.
Find your opal
Start with what we have. Or make it your own.
Explore our current opal jewellery. If nothing’s quite right, we can design a piece around the opal, colour and setting you have in mind.
There’s more to explore
Follow the piece that brought you here
Discover something different
Explore unusual gemstones, one-of-a-kind pieces and colours you may not have considered before.
An old opal you never wear?
Inherited opals often sit in drawers because the setting has had its day. See what could be kept, reset or reworked into something you’ll wear again.
October: Tourmaline
October has another birthstone. See why tourmaline comes in almost every colour, sometimes more than one at once, and how to choose one well.