ANDREA LI

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Opal
Gemstone
Guide



Opal · October Birthstone

Inside an opal's fire

Opal flashes with every color in the spectrum. Tap a marker to see where the fire comes from, and why it is the most delicate stone I set.

Opal

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Tap a marker

No two opals flash the same way. Tap a marker on the stone to see what gives opal its color, what it is made of, and why it asks for such gentle handling.

Illustrative, not a photograph.

 

 

Opal does not behave like other gems. It never grew into a crystal, it still holds water inside it, and it flashes with every color in the spectrum from a body that can be milky white, glassy, or midnight black. It is the most beautiful stone I work with, and the one I break the most. Here is what opal actually is, the kinds you will meet, and how to live with a stone this delicate.

What gives opal its fire

Hold an opal to the light and tilt it, and you see patches of color flash and shift across the stone: green, blue, violet, sometimes a rare and prized red. That is called play-of-color, and it is opal's signature.

It happens because opal is built from millions of microscopic spheres of silica, stacked in an orderly grid. When light passes through that grid, it bends and splits into its component colors, the same way a film of oil or a butterfly wing throws color without holding any pigment. The size and spacing of the spheres decide which colors you see. Tiny spheres flash blue and violet; larger ones reach all the way to orange and red, which is why red play-of-color is the rarest.

Not every opal does this. Plain opal with no play-of-color is called potch, or common opal. The stones I set are precious opal, the ones that catch fire.

The kinds of opal

Opal is really a family of stones, and they behave so differently they are almost separate gems.

TypeBodyWhat sets it apart
Australian / white / crystalLight to translucentThe classic. Pastel flashes on a pale or glassy body. The most stable opal there is.
Black opalDark grey to blackThe most prized. A dark body makes the play-of-color blaze. Most comes from Lightning Ridge, Australia.
Boulder opalThin opal on brown ironstoneThe opal is left on its natural host rock, so the dark backing gives black-opal drama in thin natural seams.
Ethiopian / WeloHoney to colorless, often very brightVivid and more affordable, but hydrophane: it drinks in water and can turn clear or change color when wet, then returns as it dries.

That last property has a name worth knowing. Hydrophane opal, which most Ethiopian Welo is, is porous enough to absorb water and even oils. Get it wet and it can go temporarily transparent or shift color, recovering only once it fully dries. It can also drink in lotions, perfume, or dye and hold a stain, so a hydrophane opal asks for more caution than a stable Australian stone.

The most delicate stone I set

I will be honest with you: opal is the stone I break more than any other. It is soft, between 5.5 and 6.5 on the Mohs scale, and it is brittle, so it has very little tolerance for stress at a single point.

From the bench

My gemstone clusters have to be wound tight, because the tightness is what makes the structure stable. With most stones that is no problem. With opal, the act of tightening can put pressure on the delicate cut point of the stone, and it cracks. I lost an expensive black opal exactly this way, wiring it into a cluster with solid 14k gold wire, which is stiff and handles much more like steel than the softer wire you might expect. That opal is still in my bag of broken stones. So I changed how I work. Now I seat the opal into the cluster last, after the surrounding structure is already set and stable, so there are no neighboring stones whose tightening can stress it. I source my opals at the Tucson Gem Show, and I choose them the way I choose all my fire: I look for brilliancy, the most vibrant flash I can find. The more alive the color, the better.

This is also why you will not find opal in every collection I make. It currently lives in my Pastel collection, but it is not a staple the way amethyst, aquamarine, or sapphire are. When I use opal, it is a deliberate choice for a stone that earns its fragility.

Caring for opal

Opal needs more gentleness than almost anything else you own.

Keep it away from all heat and from sudden changes in temperature, which can shock the stone and cause crazing, the fine network of surface cracks opal can develop. Never put opal in an ultrasonic or steam cleaner. Keep it away from harsh chemicals, and with hydrophane opal, away from prolonged soaking, perfume, and lotion.

To clean it, I use the same gentle process I recommend for all my pieces: warm water, a soft toothbrush, and a drop of Dawn to lift away oils and dust, then the polishing cloth tucked into every order to bring the metal back. No heat, no chemicals, no shortcuts. Treated kindly, an opal will hold its fire for generations.

Wearing opal

Opal is the October birthstone, which makes it a meaningful choice for an autumn birthday, and it has long been a stone of imagination and individuality, fitting for a one-of-a-kind piece.

Because it is delicate, opal is happiest in pieces that live a gentler life: earrings, a pendant, a brooch, a ring saved for occasions rather than everyday knocks. If you are drawn to a stone that is genuinely unlike any other, that holds a whole spectrum in a single cabochon, opal is for you. No two ever flash the same way.

 
 

Frequently asked questions

What is opal made of?
Opal is hydrated silica, which means silica with water still trapped inside it, sometimes as much as twenty percent. Unlike most gems, it never formed a crystal. It is hardened silica gel, which is part of why it is both so unusual to look at and so delicate to wear.
What is play-of-color in an opal?
Play-of-color is the flashing, shifting patches of color you see when you tilt an opal. It is caused by light bending and splitting as it passes through microscopic spheres of silica stacked inside the stone. The spacing of those spheres decides which colors appear, with red being the rarest.
Why do opals crack or craze?
Opal can develop a fine network of surface cracks, called crazing, usually from drying out, from heat, or from a sudden change in temperature. It is also brittle and can chip or crack from a sharp knock or from stress at a single point. This is why opal should be kept from heat, ultrasonics, and impacts.
What is a black opal?
A black opal is an opal with a dark grey to black body tone. The dark background makes its play-of-color look especially vivid and electric, which is why black opal, most of it from Lightning Ridge in Australia, is the most prized and valuable type.
What is Ethiopian or Welo opal?
Ethiopian opal, much of it from the Welo region, is known for very bright, vivid play-of-color at a more accessible price. Most of it is hydrophane, meaning it absorbs water and can temporarily turn clear or change color when wet, returning to normal as it dries. It needs more careful handling than stable Australian opal.
Is opal too fragile to wear?
Opal is soft and brittle, but it is absolutely wearable with care. It does best in pieces that take fewer knocks, like earrings, pendants, and brooches, or rings worn for occasions. Keep it away from heat, ultrasonic cleaners, and hard impacts, and it will last for generations.
How do you clean opal jewelry?
Use only warm water, a soft toothbrush, and a drop of Dawn dish soap to remove oils and dust, then a soft polishing cloth for the metal. Never use heat, steam, ultrasonic cleaners, or harsh chemicals, and avoid soaking hydrophane opal for long.
Is opal a birthstone?
Yes. Opal is the birthstone for October, sharing the month with tourmaline.

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