Stones That Hold Weather: An Introduction to Australian Opal

An opal is, technically, a small piece of water that has been trapped inside silica for many millions of years and learned how to refract light. That's the textbook version. The version I'd rather tell you is that some stones have weather inside them, and an opal is one of them.

Hold a good opal up to a window on a winter morning and you'll see the colour move. Not because the stone is moving. Because the light is. The play of colour is a function of microscopic spheres of silica stacked inside the stone in regular patterns. They bend light into different colours depending on the angle the light enters and the size of the spheres. The smaller the spheres, the bluer the flash. The larger ones give you the reds. This is the same physics that gives a peacock feather its colour, and a butterfly wing, and the underside of an abalone shell.

Australia produces the great majority of the world's opal, which is one of the small miracles of being a jeweller here. Most of the opals I work with have travelled fewer than fifteen hundred kilometres from the ground they came out of. Let me say a little about the regions, because they are the soul of the stones.

Boulder opal comes from Queensland, mostly from a handful of fields around Winton, Quilpie, and Yowah. Boulder opal is opal that has formed in seams and pockets inside ironstone, and the cutters here leave the host rock attached. The result is a stone with the opal layer floating on a backing of brown ironstone — a small piece of country, with weather inside it. Boulder opals are my favourite for this reason. They look like landscapes.

White and crystal opal come mainly from Coober Pedy in South Australia, the underground opal town where many of the residents live in dugouts to escape the heat. White opal has a pale body — milky white or grey — through which the colour plays. Crystal opal is similar but its body is translucent, which means the colour seems to come from deeper inside the stone. These are luminous, gentle stones.

Black opal comes from Lightning Ridge in New South Wales. The body tone is dark — brown to black — and the play of colour comes up against the dark like a sunset against a night sky. Black opals are the most expensive of the four because the dark body intensifies the colour. The very best of them are extraordinary, and very rare.

There are also matrix opals (where the opal is intergrown with the host rock in fine veins), Yowah nuts (small natural opal-filled concretions found near Yowah), and various other regional varieties. Each has its own character. None of them photograph well. All of them are better in your hand.

If you're new to opal, here are a few things worth knowing.

Play of colour is what you're paying for. Not the body tone, not the size, not the cut — the play of colour. Look at the stone in good light, tilt it, and watch how the colour moves. A small stone with brilliant fire is worth more than a large stone with weak fire.

Bigger isn't always better. A small boulder opal with a clear green flash will outshine a large one with a muddy display.

Opal is softer than diamond, sapphire, or even quartz. Take it off before sport, before cleaning, before sleep if you tend to grind. Treat it gently and it will last generations. There are family heirloom opals in this country that have been worn daily for a century.

If you've ever wondered why two opals never look the same in a photo, even side by side — that's the weather inside them, refusing to be photographed.

Come to Paddington Markets on Saturday morning. The light is honest there, and I have a small tray of opals you can hold up to it.