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How To Tell If Opal Is Real: The Best 12 Foolproof Tests

Opal is the birthstone of October, and is said to symbolize faithfulness and confidence.

There are many different types of opal, some worth more than others, and they occur naturally in many different colors.

Though opal is considered soft, it’s still a great choice for delicate jewelry and statement pieces.

natural boulder opal gemstone

If you’re interested in opal, it helps to know how to tell if opal is real.

This way, you’ll get your money’s worth. A lot of people wear/have synthetic and even imitation opals, and that’s perfectly fine.

But if you want to get your hands on real opal, this is what you need to know::

The story of opal

Some say we get the name ‘opal’ from the Greek word ‘opallius’, meaning ‘to see a change in color’, because they come in so many different colors.

Others say it’s from the Latin word ‘opalus’, meaning ‘precious jewel’. Wherever it came from, it’s the name of one of nature’s most beautiful creations.

Opal is the national gemstone of Australia. First Nations people considered opals to be the footprints of the Creator on Earth.

They wore them as necklaces to ward off evil and believed dreaming of opal meant good luck.

This is interesting because, for a long time, opals were widely believed to be bad luck in the West.

This vicious rumor is believed to have been started by De Beers, the world’s largest diamond corporation.

The goal was to get people to buy more diamonds! Unfortunately, opal was unable to shake off the bad press and sales drastically declined during the peak of these rumors.

Today, it’s safe to say that things have changed (somewhat). Some will never get caught near opal, others say it can only be worn by people born in October.

Many people don’t even know about this rumor!

Rumors aside, let’s get into the facts and how to tell if opal is real. Let’s discuss how Australia’s national gemstone has been mined, synthesized in labs and imitated.

Natural opals

While Australia has made opal their national gemstone, the first opals were actually discovered in Kenya and Ethiopia.

Historians date these discoveries to as early as 4000 B. C. Opals later became symbols of wealth and status, and the use of precious opal spread across the world.

Most of the world’s current opal supply is of Australian origin. Mining also occurs in places like Hungary, Mexico, Peru, Brazil, Honduras and western parts of the United States.

Natural opals are not considered minerals. They lack the crystal structure that is required for that category, like obsidian, pearl and amber.

Instead, they are clusters of amorphous hydrated silica, with a water content of between 3% and 21%, and are considered mineraloids.

This is why opal reflects differently, giving its signature rainbow shimmer.

Because of their high water content, opals are extremely prone to cracking.

This is more likely in environments of high temperature or extended low humidity.

Natural, or solid opal has not been treated or altered. They are mined, polished, cut and sold in their natural state.

This means they fetch a much higher value, especially for rarer types like black opal.

Opal scores 5.5-6.5 on the Mohs Hardness scale, and is one way to tell if opal is real.

How are natural opals graded?

You may be used to the 4Cs with diamonds and rubies, but natural opals are graded and valued using somewhat different criteria.

These include:

1. Color 

Play-of-color, body tone/background, pattern and brightness. These refer to the appearance of the stone in terms of how it reflects colors and how well it does so.

2. Clarity

Clarity includes factors like transparency, inclusions and type. Opals can be transparent, translucent or opaque.

They can be composed entirely of opal or carry remnants of the host rock. Inclusions such as cracks, pits, crazing and potches lower their value.

3. Cut

Opals that are asymmetrical or irregular fetch lower prices. Other factors include thickness, polish and calibration.

4. Carat weight

Large opals are typically more expensive than smaller opals. However, this is not a hard-and-fast rule because rare, small opals, like black opals with brilliant play-of-color, can be more expensive.

5. Additional factors

Other important grading factors include origin, or where the opal was mined, along with whether it’s solid opal or an assembled rock.

7 types of natural opals

It’s hard to choose a set color and say this is how opals occur naturally, because there are many different types of natural opals, even colorless opals.

This can make it a bit more difficult to check if an opal is real because it can’t be judged solely by this physical property.

Here are some of the many different types of natural opals:

Black opal

Let’s start by first saying not all black opals are black. Generally, the backgrounds of black opals are dark and can range from dark-gray to blue-black due to iron oxide.

These opals still reflect all colors of the rainbow. Some do so more brilliantly than other backgrounds, making them the rarest, most expensive type of opal.

Most black opals come from Australia and can fetch prices more expensive than diamonds!

Boulder opal

It’s easy to get black opal and boulder opal confused. Boulder opals have dark backgrounds as well.

The difference lies in the formation. Boulder opals form within thin veins of ironstone boulders and carry a brown rock impression on their back from their host ironstone.

This type of opal is referred to as a natural doublet because the dark back color comes from its host.

White opals

White opals have white opaque to translucent backgrounds or body color, and distinct play-of-color.

They are very common and are the least valuable of all opals. These are some of the most imitated types of opals and many people don’t know how to tell if an opal is real if it’s white.

Crystal opals

Crystal opal, or water opal, is completely or partially translucent. It is made of pure hydrated silica and does not contain the oxides that turn opal black or white.

In water opals, the play-of-color is very small and faint. Crystal opals on the other hand do a better job at showcasing the brilliance of this gemstone.

Fire opals

Fire opals, or dragon’s breath, are translucent to semi-opaque. They occur naturally in shades of yellow to bright orange, and can even be red.

They are found mainly in Mexico, but have also been mined in Java, Turkey, Kazakhstan and Brazil.

Fire opals are prized for their hues and not necessarily their play-of-color.

Ethiopian welo opals

These come from the Welo Province in Ethiopia. It’s a hydrophane that makes the opals less susceptible to crazing, and they come in stunning shades of red.

Peruvian opals

Peruvian opals are typically blue opals, but can also come in pink. These are found in Peru and come in opaque and semi-opaque transparencies.

How much do natural opals cost?

The most expensive opal ever sold was found in Australia in 2003 and is worth over 1 million dollars.

It is named the Virgin Rainbow and was formed within the skeleton of a Belemnite (cuttlefish).

Black opal can cost as much as 100x more than a diamond! They can sell for up to $10,000 per carat but usually range from $10-$6000 per carat. Opal is even more expensive than gold!

More common opals like white, red, pink, blue, green, and fire opals sell for as low as $10 per carat, up to as much as $500 per carat.

Rainbow opals average $10-$1000 per carat.

Are doublets and triplets “real or fake opals”?

Doublets and triplets are assembled stones. Along with natural opal, they come with thin, durable backings to improve the strength of the stone.

Doublets come with a thin layer of opal, plus a backing. The backing is usually made of obsidian, black glass, common opal, and even plastic to create an opal with two, or double layers.

Triplets, on the other hand, are opals with three layers. They are opals cemented between a backing and a dome covering.

Doublets and triplets are more affordable and are more suited for making jewelry.

Here’s how to tell if opal is real when made into doublets and triplets:

1. How to detect doublet opal

Start with the body tone. If it’s solid white, then it’s most likely a pure opal.

Look at it from the side. If you see an uninterrupted line around its perimeter, then it’s most likely a doublet.

From the back, opal doublets are a bit harder to spot, but generally, if the backing is perfectly flat or even, then it’s likely not pure.

Over time, even the most expensive doublets will begin to cloud. This happens as it becomes worn out and the glue becomes weaker, allowing water to penetrate.

2. How to detect triplet opal

Triplets, like doublets, are composed of layers and are not translucent. Turn the opal you suspect on its side and look out for the backing, the thin piece of opal and a plastic/glass dome.

It will also look a bit glassy at the top and will wear away and become cloudy.

Lab-created or synthetic opals

Pierre Gilson first synthesized opal in 1974. He is the same man who synthesized turquoise and lapis lazuli.

These first attempts created opal with lizard-skin patterns that were obvious synthetics.

They have since improved to the point of being more beautiful than many natural opals.

Even experienced gemologists sometimes have trouble telling them apart.

The only thing that distinguishes synthetic opals from natural opals is how they were created.

Besides that, natural and synthetic opals have the same chemical and structural composition.

Appearance and physical properties are also the same.

4 types of synthetic opal

Sellers are required to let people know if they’re getting a synthetic opal, though there are many who prefer a synthetic over the natural thing anyway.

You can get an amazing-looking synthetic opal for just a few dollars, and if you compare that to what it would cost if it was natural, it’s more than a bargain.

Here are 4 of the most popular types of synthetic opals on the market today:

Gilson labs opals

These are among the first types of opal to be synthesized using resin-free procedures.

Gilson opals are what most people think of when they hear about synthetic opals.

These synthetics have a lower water content, making them stronger than natural opals.

These opals come in seven beautiful color combinations.

Aurora opals

Unlike natural opals that are formed from silica, aurora opals include a special polymer.

This makes them more durable and suitable for jewelry making. They feature a black or white body color with green as the most common color, and non-directional swirls.

Sterling opals

A fun fact about sterling opal is that it’s one of the only synthetics that do not use dye in the production of the opal.

Also known as the monarch opal, this type of synthetic opal includes veins or ‘potch lines’ that are unique to natural opals.

The purpose of this was to make them look more natural. In reality, this is a double-edged sword as people have been duped into buying this synthetic thinking it is real opal.

Mexfire opals

If Mexican fire opals are such a hit, it shouldn’t surprise you that synthetics of them exist.

The physical and gemological properties are very similar. The only way to tell the difference between natural Mexican fire opals and Mexfire synthetic opals is by doing a specific gravity test.

How to detect synthetic opals

Detecting synthetic opal isn’t always easy, and it may require expertise on the matter to tell some really good ones apart.

Nevertheless, here’s how to to check if an opal gemstone is real or synthetic:

3. Growth pattern

Under magnification, observe the play-of-color patches on the opal and their growth direction.

Opal created in a lab will show a columnar growth pattern when viewed perpendicular to the growth direction.

The drawback to this test is that you need to use lab equipment, but it is reliable.

4. Chicken-wire/snakeskin pattern

Over time, modern approaches have solved this problem, but it’s still very much present in low-value, poorly made synthetic opals.

To test this out, you will need a 10x loupe. If you don’t have one, you’ll need an expert on how to tell if the opal is real.

5. Specific gravity test

Manufacturers often miss the mark on the specific gravity of synthetic opal, which is lower than natural opal.

Opal has a specific gravity of 2.10 (2.00 for fire opal). To do this test, you will need a scale, a beaker with water and the opal.

Measure the opal on its own, then measure it when in the water. Divide the measurement of the opal on its own by the measurement in water.

This is a pretty reliable test, but without the equipment, it isn’t possible.

It may mean buying a scale or visiting a lab.

6. Uniformity

Pay close attention to the uniformity of the play-of-color patches. These occur in patterns, however, in natural opals, there’s no uniformity in their size or distribution.

Use a bright light to observe these patterns. If it’s too perfect or ‘matchy-matchy’, then it’s a synthetic.

This is a pretty reliable test, and you don’t need any fancy equipment to carry it out.

7. Color

Synthetic opals give themselves away with their large, bright patches of color.

If it looks too perfect, chances are it was made in a lab. Is the color a part of the stone, or does it seem to only occur on the surface?

The latter means it is synthetic opal.

Combine this test with the price you paid. Large opals with bright play of color are expensive.

If you paid $20 for it, it isn’t natural. For greater reliability, observe the opal under a spectroscope.

Staining opal creates absorption bands.

Imitation opals (or fake opals, or opal simulant)

Imitation opals are in a different category from lab-created opals. This is because they have an entirely different chemical composition from natural opals.

Imitation opals typically contain much more resin than silica, and some are even created without water.

They are typically made of glass, resin or plastic and are much cheaper than earth-created or lab-created opals.

They have their place, usually in cheaper jewelry.

Unlike synthetic or lab-created opals, fake opals or opal simulants are much easier to detect, and some can be distinguished using the naked eye.

Let’s talk about the most popular types of opal simulant:

5 popular imitation opals

The manufacturer of the imitation opal and the formation process used heavily influence how realistic it is.

Many imitation opals are created using the latest technology and techniques.

This makes telling them apart harder than it should be.

Here are 5 popular imitation opals:

Slocum stone

John Slocum created this imitation in 1974. It is made of silicate glass that includes flake-like metallic film to create play-of-color.

These imitations were very popular upon their release, but synthetics like Gilson stones made them less relevant.

Opalescent glass

This is one of the most popular types of fake opal. They are created by cooling molten glass slowly, which forms crystals and gives the imitation a ‘milky’ appearance.

This closely mimics the translucency of natural opal, making them look more realistic.

Kyocera opals

Japanese company, Kyocera, created a special type of fake opal made of plastic resin and silicon.

This is considered one of the better imitations because it does not have that snake-skin or chicken-wire pattern.

Under magnification, however, the patches are perfectly uniform, another indication it is a fake.

Unlike natural opal which has a specific gravity of 2.00, this fake has a specific gravity of 1.35, making this the best way to distinguish them.

These opals also burn to create a strong odor, indicating high levels of plastic.

Oparex opal

This imitation was also created by Kyocera. It is a resin colloidal imitation opal that uses about 25% silica, along with resin to create an imitation that looks very similar to aurora opals.


Opalite imitations are special because they’re able to match the play-of-color of natural opal.

However, they have high resin content, and a negligible amount of silica, which makes them count as fake.

They may not be easy to distinguish under magnification, but specific gravity tests work well.

How to tell if opals are fake

You can use some of the same techniques you used to tell synthetic opals from real opals to detect imitations.

Here are some other tests you can use to check if opals are fake:

8. Play-of-color

In real opal, the play-of-color is organized in a random fashion, so uniformity is a red flag.

Similarly, real opal has an even spread, meaning the color is not concentrated on the surface, or at a layer just below it.

Use a microscope or loupe for this test. It is relatively reliable and is useful for field testing.

9. Soot (brown/black points)

Real opal either has dark backing, as in the case of doublets, triplets and boulder opal, or is translucent.

There should be no black or brown points to indicate heat treatment. You can typically observe this with the naked eye.

This test is very reliable and should give you an answer within seconds.

10. Appearance

Look at your stone from every angle. Real opal is solid and is not made of different layers unless it is a doublet or triplet.

This is a relatively reliable test, but it may be easy to miss something with the naked eye.

11. Fluorescence

Shine a very bright UV light against the surface of the opal. This is a great test for distinguishing if opal is real because real opals fluoresce.

This test only requires the use of a flashlight to check if an opal is fake and it is highly reliable.

12. Refractive index

Natural opal has a refractive index of 1.3-1.5. To conduct this test, you will need a refractometer, RI liquid and a bright light source.

It’s better to seek the help of an expert to get an accurate measurement as this test may be too complex to perform at home.

It is, however, very reliable, and will let you know for sure if the opal is fake.

Final words

Besides synthetic opal and fake opal, buyers have also been duped by other gemstones posing as opals.

Fire agate is one example that is often sold as fire opal. Other gemstones that frequently mimic opal include labradorite, moonstone and chalcedony.

You may not be able to perform many of these tests when buying opal, so a good way to know you’re getting what you pay for is by asking about its origin.

Remember, most opals come from Australia, but others come from Mexico, Peru, Ethiopia, Brazil and Hungary.

Having a natural opal may sound very attractive, but synthetics are just as stunning.

Consider opting for one of the top-of-the-line synthetics, especially when buying jewelry.

They give you the look with the durability that natural opals lack. Plus, you’ll end up spending much less on it.


How to tell if an Ethiopian opal is real

Use properties like play-of-color and uniformity to tell if an Ethiopian opal is real by using a microscope.

How to tell if opal is real in a ring

Beware of rings that conceal the back and side of the opal. Use a magnifier to observe the patterns within the stone, and look for bubbles (this means it’s glass).

How to tell if a white opal is real

It’s almost impossible to tell if white opal is real using the naked eye. If you can’t perform tests, ask about their origin.