To tell if an opal is real, look at three things: the side of the stone, the pattern of the color and the way the color moves. A natural solid opal is one piece of material all the way through, and its play of color sits in irregular patches, flashes and rolling bands that shift as you tilt it. A doublet or triplet shows a straight seam on the side where a thin slice of opal is glued to a dark backing, sometimes under a clear dome. A lab-grown opal, such as the Gilson stones made since the 1970s, has color in tidy, repeating cells that look like lizard skin or chicken wire, and under a loupe the side shows a columnar, stacked structure. Glass and plastic imitations either show no true play of color or show color that looks printed or trapped like foil. Most opals found in old jewelry boxes are natural white opal or doublets worth tens of dollars, while fine black opal from Lightning Ridge can reach thousands per carat.
Quick answer
- Check the side first. A straight line between layers means a doublet or triplet, not a solid opal.
- Neat, repeating cells of color that look like snakeskin point to lab-grown opal. Natural color is irregular.
- Common white opal is worth approximately $5-100 per carat in jewelry terms. Doublets, triplets and lab opal sell for tens of dollars per piece.
How to check yours, step by step
- Look at the stone from the side. Turn the ring or pendant so you are looking along the edge of the stone, level with the top of the setting. You are looking for a straight, even line where two materials meet. A dark band at the bottom with a thin colorful layer on top is a doublet. A colorful middle layer under a clear, glassy cap is a triplet. A closed bezel that hides the whole side is not proof of anything, but it is common on doublets for that reason.
- Check the top for a glassy dome. Tilt the stone under a lamp and look at the reflection. Quartz or glass caps on triplets reflect like a window, very bright and slick, and the color seems to sit slightly below the surface. Natural opal has a softer, slightly waxy shine.
- Read the pattern of the color. Use a 10x loupe or the macro mode of a phone. Natural opal shows color in irregular patches, pinpoints, ribbons or broad flashes, with no grid. Lab-grown opal shows small cells of color with a scaly outline, all roughly the same size, often described as lizard skin or chicken wire. Glass imitations such as Slocum stone show flat, crinkled flakes that look like foil.
- Watch the color move. Rock the stone slowly under one light. Play of color in real opal, natural or lab-grown, switches on and off and changes hue as the angle changes. A stone that just glows blue on one side and orange against the light, with no separate flashes, is usually opalite, which is glass.
- Look at the back. Turn the piece over. An open back on a ring or pendant often shows the underside of the stone. Black plastic, black glass or a perfectly flat, polished dark back suggests a doublet. Brown ironstone on the back with veins of color running into it suggests boulder opal, which is natural.
- Check for crazing and cloudiness. Under the loupe, look for a fine web of cracks on the surface or inside. That is crazing, from the opal drying out, and it lowers value sharply. A grey, milky haze between layers of a doublet usually means water got into the glue.
- Check the setting and the mark. Read the stamp inside the shank or on the bail. Solid opals are often set in 10K, 14K or 18K gold. Triplets and lab stones turn up in sterling and in plated settings. The metal does not prove the stone, but it tells you what level of jewelry you are dealing with.
The main types of opal and opal look-alikes
Opal is a hardened silica gel that holds around 3 to 10 percent water. The play of color comes from tiny spheres of silica stacked in a grid that diffracts light. Lab-grown opal copies that structure, which is why it has real play of color, and why its too-perfect order is what gives it away.
| Type | What it is | What you see | Typical value |
|---|---|---|---|
| Natural white or light opal | Solid opal with a milky white body | Pastel flashes on a white base, irregular pattern | $5-100 per carat, more for bright full color |
| Crystal opal | Solid, transparent to translucent opal | Color that seems to float inside clear material | $50-500 per carat |
| Black opal | Solid opal with a dark body tone, mostly from Lightning Ridge, Australia | Vivid color against a near black base, seen from the top and through the stone | $200 to several thousand per carat, top gems far higher |
| Boulder opal | Opal in seams on brown ironstone, Queensland, Australia | Thin veins of color with natural brown stone on the back or around it | $20-1,000 per carat depending on color and thickness |
| Ethiopian (Welo) opal | Solid, often hydrophane opal from Ethiopia, common since about 2008 | Bright, honeycomb or broad-flash color, often in a yellowish or clear body | $10-150 per carat |
| Fire opal | Mexican opal with an orange to red body, sometimes no play of color | Transparent orange stone, may have little or no flashing color | $10-300 per carat |
| Doublet | Thin slice of natural opal glued to black potch, ironstone or glass | Seam visible from the side, flat dark back | $10-80 per piece |
| Triplet | Doublet with a clear quartz or glass dome on top | Seam visible from the side, glassy top | $5-50 per piece |
| Lab-grown opal (Gilson, Kyocera and others) | Synthetic opal with the same structure as natural | Regular, scaly cells of color, columnar structure from the side | $2-20 per carat, more in brand-name pieces |
| Opalite and other glass | Milky glass with a blue sheen | Blue glow and orange back light, no separate flashes | A few dollars |
| Plastic imitation and resin | Molded plastic, sometimes with flakes inside | Light, warm to the touch, color often looks printed | A few dollars |
Value for natural opal depends on body tone (black is highest, then dark, crystal and white), brightness, the pattern of color, how much of the face shows color, and whether the stone is crazed or cracked. A dull white opal with a few faint pinpoints of green is a different stone from a white opal with bright red flashes across the whole face, even at the same size. Red is the rarest flash color and adds the most.
Natural, lab-grown or doublet: a side by side
| Clue | Natural solid opal | Lab-grown opal | Doublet or triplet |
|---|---|---|---|
| Side view | One material, top to bottom | One material, often with a fine columnar grain | Straight seam, dark backing, maybe a clear cap |
| Color pattern | Irregular patches, flashes, ribbons | Even, repeating scaly cells | Natural pattern on top, since the slice is real opal |
| Back | Same material, or brown ironstone for boulder | Same material | Black potch, ironstone, glass or plastic |
| Weight in hand | Light, but solid | Similar to natural | Similar, triplets slightly heavier |
| Cost to replace | High for good color | Low | Low |
| Typical setting | Gold, sometimes fine silver | Silver, gold plate, modern gold | Silver, gold plate, souvenir pieces |
Black opal and boulder opal
Black opal is the most valuable kind. The dark body tone makes the play of color look intense, and the best stones come from Lightning Ridge in New South Wales. Many stones sold as black opal are in fact doublets or triplets with a black backing, because a thin slice of white or crystal opal on black potch looks remarkably like a solid black stone from above. The side view is the honest test. A solid black opal is dark through the body. A doublet is light on top and dark below a line.
Boulder opal can look like a doublet at first because it has a dark back too. The difference is that the back is natural brown ironstone, usually with an uneven surface and with opal veins that wander into it. There is no perfectly straight glue line. Boulder opal is often cut in freeform shapes that follow the seam, which is a helpful sign in itself.
Crazing, water and care
Opal holds water, and when it loses too much it can craze, forming a network of fine cracks. Crazing is permanent and can reduce a valuable stone to a fraction of its worth. Some Mexican and older opals are more prone to it.
Ethiopian Welo opal is often hydrophane, which means it absorbs water. Soak it and it may turn clear and lose its color for hours or days before drying back. That is normal, not damage, though oils and dyes can be absorbed the same way. Doublets and triplets should not be soaked at all, because water gets into the glue and leaves a grey cloud that cannot be fixed. If you are unsure what you have, keep it dry and clean it with a damp cloth only.
Treatments also matter. Some Ethiopian and Australian Andamooka opal is smoke or sugar treated to darken the body and imitate black opal. Under a loupe, treated stones may show small black specks or a peppery look in the color patches.
What a photo can show and what only a gemologist settles
A clear photo shows a lot: the side seam of a doublet or triplet, the lizard skin pattern of most lab-grown opal, the blue glow of opalite, crazing on the surface, ironstone on the back of boulder opal and the mark in the setting. That is often enough to place the stone in the right group and estimate a value range.
A photo cannot tell some high-quality lab opal from natural when the cells are small, cannot read body tone accurately under warm indoor light, and cannot detect smoke or sugar treatment reliably. A gemologist with a microscope and the right light settles those questions. For anything that looks like solid black opal, or any stone larger than a few carats with strong color, that is worth doing before selling.
If the stone sits in a gold setting, the metal can be worth more than the opal. Our guide on how to tell if gold is real covers the stamps and the weight math.
Common mistakes
- Calling every dark opal a black opal. Most dark-looking stones in older jewelry are doublets or triplets with a black backing.
- Mistaking boulder opal for a doublet because of the dark back. Boulder opal has a rough, natural ironstone back with no straight line.
- Soaking a doublet or triplet to clean it. Water in the glue layer leaves a permanent grey haze.
- Treating opalite as opal. It is glass with a blue sheen and no play of color.
- Pricing by size alone. Brightness and the color pattern matter more than carat weight for most opals.
- Ignoring crazing. A crazed stone, even a large one, sells for a small share of an intact stone.
- Assuming a sterling or plated setting means a fake stone, or a gold setting means a natural one. Both happen the other way around.
What to photograph
- The top of the stone in daylight, and again under a single lamp, tilted to show the flashes.
- A macro shot of the color pattern, as close as the phone can focus.
- The side of the stone at eye level, showing any seam, dome or backing.
- The back of the piece, especially if the setting is open.
- The stamp inside the ring or on the bail.
- Any cracks, chips or dull patches, so the estimate reflects them.
When to get it looked at in person
- A gemologist with a microscope can separate natural, lab-grown and treated opal and confirm a solid black opal. Expect roughly $50-150 for a single stone report from an independent gemologist, more for a formal lab report. Worth it for any stone that looks like solid black or crystal opal with bright full color.
- A jeweler can look at the side of a stone in a closed setting with a loupe and test the gold. Many will do a quick look at no charge if you are a customer.
- An appraiser charges roughly $50-150 per piece or $100-300 an hour. Worth it for insurance, estate division or a piece with several significant stones.
- An opal dealer often pays more for good natural opal than a general jeweler and knows Australian material well. Worth contacting for large or high-color stones.
For other stones in the same box, our guides to real pearls and real diamonds follow the same approach.