Opals are captivating stones. Their play-of-color, the way light dances across their surface, feels almost otherworldly. But not all that glitters is natural. The market is flooded with synthetic and imitation opals, and telling the difference isn't always easy at first glance. Whether you're buying a piece of jewelry or examining an old family heirloom, knowing how to tell if an opal is real matters - both for its value and its story.
Start With the Basics: Natural, Synthetic, and Imitation
There’s more than one kind of “fake” opal, so first it's important to understand what you might be looking at.
A natural opal forms in the earth over millions of years. It's cut and polished but otherwise unchanged. These are the most valuable and often the most beautiful.
A synthetic opal, also called lab-created, is made in a controlled environment. It shares the same chemical and structural makeup as a natural opal but lacks the age and rarity. Some are easy to spot, but high-end synthetics can be incredibly convincing.
An imitation opal is a different material altogether - often glass or plastic - made to mimic the appearance of an opal. These are the least valuable and usually the easiest to identify.
Now that we’ve set the scene, let’s get into the signs to look for.
Examine the Play-of-Color
This is the most famous feature of opals: that mesmerizing flash of color that seems to move inside the stone.
In natural opals, the play-of-color is usually uneven, irregular, and layered. It moves as you tilt the stone, but it doesn’t repeat in a pattern. It can look like sparkles, flashes, broad strokes, or even a rolling wave of color.
Synthetic opals often have a color pattern that looks a bit too perfect. You might see what’s called a "lizard skin" or "snake skin" effect - a repeating, organized pattern that almost looks pixelated or tiled.
Imitation opals usually lack true play-of-color. Instead, they may look cloudy, too glittery, or have colors that sit flat on the surface. If the color looks like it’s just painted on or trapped inside glass, you’re probably not dealing with the real thing.
Look From the Side
This is one of the simplest but most telling ways to check an opal. Hold the stone and tilt it to view it edge-on.
Natural opals are usually cut as a solid piece or as a doublet or triplet. A solid opal is one continuous piece of opal throughout. A doublet has a slice of opal glued onto a backing (usually black potch or ironstone). A triplet adds a clear domed cap, often quartz or glass, over the opal slice.
If you see a visible line between layers - especially if the top layer is highly reflective or domed - it’s likely a triplet or doublet. These aren’t fake, but they’re not solid opals and are worth significantly less.
In synthetic opals, the layers may be visible too, but the color pattern usually gives them away more than the structure.
Imitations often don’t have layers at all. Instead, the entire stone may appear completely uniform or have bubbles inside if it’s made of glass.
Feel the Weight and Temperature
Real opals, even small ones, tend to feel cool to the touch at first. They also have a slightly heavier, denser feel than imitations. Plastic or resin imitations will often feel warm and very lightweight.
This isn’t a perfect test, but when combined with visual inspection, it helps.
Under Magnification, Look Closely
If you have access to a jeweler’s loupe or even a good macro camera, look closely at the structure inside the opal.
Natural opals don’t have a perfect internal structure. You might see inclusions, subtle cracks (called crazing), or an irregular distribution of color. That’s normal.
Synthetic opals, on the other hand, often have a "columnar" structure - almost like vertical lines or stacked bricks inside the stone. Some are so clean and uniform that they start to look artificial even before you spot the structure.
Imitation opals might show tiny air bubbles (especially if made of glass) or no internal structure at all.
Trust the Back of the Stone
It’s easy to focus on the flashy part of an opal - the front - but don’t ignore the back.
A natural solid opal will have an uneven or rougher back, sometimes with sandstone, ironstone, or potch (a dull, grey material) still attached. It may also show signs of natural wear.
If the back is glossy, black, and suspiciously smooth, it might be a resin or glue backing, common in doublets and triplets. These can still be used in fine jewelry, but they’re not solid opals.
And if the back is completely clear, glassy, or looks molded - that’s likely a synthetic or imitation.
Price Should Match the Stone
If you’re holding a vibrant, large opal with strong color play and no inclusions - and it’s being offered for a suspiciously low price - be cautious.
Real opals, especially black opals or boulder opals with vivid colors, can be expensive. While you can find small or lower-grade natural opals for reasonable prices, a high-quality stone will rarely be cheap.
This doesn’t mean every expensive opal is real, but a price that feels too good to be true often is.
Ask for Documentation
Reputable sellers of natural opals should be able to offer a certificate of authenticity or at least explain the stone’s origin and type. If you’re buying online, look for detailed photos from multiple angles, including the side view and back.
Many natural opals come from Australia, Ethiopia, or Mexico. Sellers who disclose the origin, the cut (solid, doublet, triplet), and whether it’s natural or lab-created are far more trustworthy than those who don't.
Know What You're Looking At Before You Buy
Opals are a wonder of nature, but they’re also one of the most imitated gemstones on the market. Learning how to spot the real thing - by understanding structure, pattern, feel, and origin - is the best way to protect your investment and appreciate what you're wearing.
The good news is that once you’ve seen a few side by side, the difference becomes clear. Real opals don’t just catch the light. They carry it.
