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Opal is highly praised for its kaleidoscopic play-of-color. Sometimes opal’s mesmerizing optical effect compared to fireworks, jellyfish, galaxy, or lightning. To make the opal affordable to a wider range of people, a lot of different fakes have been created.
The most common fake opal is assembled stone. Doublets or triplets can be distinguished by the side view, in case they are not enclosed into metal. Plastic, glass, and synthetic fake opals are also widespread. Unlike the natural opal, they can have a columnar structure or lizard skin surface texture.
As the gem market is flooded by fake opals and fake opals prices are quite high, it’s necessary to be prepared. Further, you will have full disclosure of what is natural opal; how do natural opals from different localities vary; the most common types of fake opals; and, of course, a comprehensive guide, which will help you to differentiate a natural gem from a fake one.
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How to Tell if Opal is Real
Opal, unlike other gemstones, is not a mineral. Opal is a mineraloid. It means that opal doesn’t have a crystal structure. It is an amorphous and hydrated version of silica. Opal is made up of microscopic spheres arranged in a grid-like pattern.
Water content in opals can reach up to 20 percent. That is why the recommendation to store opal away from sunlight exists. Opal occurs in rock fissures. Some of the rocks where opal can form include basalt, limonite, and rhyolites.
Real opal possesses a magnificent play-of-color, or iridescence spread evenly, but not in an irregular pattern. It occurs in a variety of colors: from white through the whole rainbow specter to black. It has no brown spots of soot or columnar structure.
Play-of-color or opalescence occurs in precious opal because of light diffraction. When the lightwaves travel between the spheres of silica, they diffract or bend.
As they bend, they break up into the colors of the rainbow or spectral colors. And we can observe the result of this process as play-of-color or iridescence.
The color depends on the sizes of the spheres. Spheres that are approximately 0.1 microns (one ten-millionth of a meter) in diameter produce violet. Spheres about 0.2 microns in size produce red. Sizes in between produce the remaining rainbow colors.
Australia is the biggest supplier of opals in the world (from 80 to 95 percent), and opal is the national gemstone of the continent.
How to Identify Real Opal?
To identify real opal, view it from the side. Real opal is solid. It is not composed of different layers; it has no column structure or lizard skin effect on the surface. Real opal is made of silica, not from glass, plastic, or resins. Real opal is very homogeneous from different sides.
- Real opal is a solid stone. Which means it is not glued or fussed from different parts.
- Real opal has evenly spread play-of-color through the whole body and looks the same from the front and the side view.
- Real opal has no columnar structure viewed from the side.
- Real opal has no lizard skin or snakeskin effect, which means a regularly ordered pattern of color flashes on the stone surface.
- Real untreated opal should not have any soot points, which indicated that the stone was smoked or sugar treated.
Identifying Real Fire Opal
The real fire opals are that of yellow, orange, and red colors and display a distinct play-of-color. They are homogeneous when viewed from different directions, have no ordered column structure or lizard skin effect.
The real fire opal comes from two countries Mexico and Ethiopia. Sometimes they have other trade names, such as Cantera opal, Shewa opals, Mezezo opals, and Welo opal (wollo or wello).
Identifying Real Pink Opal
The most important characteristic of real pink opal is its milky pink uniform color. It’s OK to be translucent or semi-opaque for a real pink opal. Most real pink opals come from Peru. So do not hesitate to ask the origin of the stone.
The real pink opals do not occur in the form of big boulders. They are about half of the centimeter across and range in color from nearly white through carnation pink to lilac.
Real pink opals are mixed slightly with chalcedony during the formation process, that’s why they are somewhat harder than other types of opals.
Identifying Real White Opal
It’s almost impossible to identify real white opal with the naked eye. The best professional advice we can share with you is to ask the dealer about the origin. If the origin has stayed as Coober Pedy or Mintabie (Australia), you can be safe.
Real white opal is translucent to opaque-white or other light color backgrounds with distinct play-of-color.
Identifying Real Black Opal
The Black opal is a term used for opal that has a dark body color, usually black or dark gray. The term is also applicable to opal that has a dark blue or dark green body color.
Real black opal is the rarest and the most expensive type of opal. That is why most opals are smoked to enhance the body color and raise the price.
Real black opals should not have any soot patches on the surface, which tell about smoke or sugar treatment. It’s always a good idea to check the origin locality. For real black opals, they are Lightning Ridge, New South Wales, Mintabie, or Coober Pedy, South Australia.
Identifying Real Blue Opal
Real Peruvian blue opal (also called blue opal) is a semi-opaque to opaque blue-green or turquoise-color gem. It does not display a play-of-color. The color is milky and homogeneous.
Blue opal also comes from Oregon and Idaho in the Owyhee region, as well as from Nevada around the Virgin Valley.
Identifying Real Mexican Fire Opal
Mexican Fire Opal has a bright red, orange, or yellow background color mostly transparent or translucent. Most of them do not have precious iridescence, but still, these warm colors of natural red Mexican opals are highly praised.
Real Mexican fire opals have their own very specific type called Cantera Opal. Orange color opal enclosed into a rhyolites host rock. Cutters simply cut a cabochon from rhyolite with a fire opal window in the dome.
Identifying Real Ethiopian Opal
Real opals from different locations have no specific characters as, for example, some exotic inclusions in sapphires or emerald can disclose their provenance.
A good tool to distinguish a real Ethiopian opal among Mexican or Australians is to check the trade names: Shewa opals, Mezezo opals, welo opals, wollo, and wello opals. Also, Ethiopian opals are usually very porous. So the specific gravity of this type of opal is slightly lower.
Much of the Ethiopian opal produced from the Wollo province has an orange, yellow or reddish body color along with play-of-color.
Identifying Real Australian Opal
Most of the opals available on the market came from Australia.
The best way to identify the real Australian opal is to ask the direct locality where the opal was mined. They are Coober Pedi, Mintabie Opal Field, Andamooka, Lightning Ridge, Jundah, and Quilpie. Some real Australian opals are formed in the iron-rich rock called ironstone and have wooden structures.
TIP: Australian opals are one the coolest rocks you can find or own. Do you know what are other cool rocks? Find out more about them in the article below:
How to Tell if Opal is Fake
Before the identification of fake opal, let’s differentiate the most common types of opal fakes.
Fake opal made of glass can be identified by tiny films inside, round bubbles, or swirls. Fake opals made of plastics and resins will have very even opalescence, which is regularly ordered. Assembled fake opals are made of two or three layers, which are visible from the side view.
Classic Fake Opals
The common types of fake opals are made from:
A manmade glass is an age-old gem imitation widely used today. Modern technologies allow the production of a glass of any color.
That is why it is the most popular imitation of many gems. Opal is not an exception. Glass material is known as “Slocum stone” can mimic the appearance of opal.
Slocum stone is a silicate glass with thin translucent flakes of iridescent film, which produce opal-like play-of-color.
Opalescent glass is the other widespread opal simulant. It is a man-made glass with a sheen-like luster which is perceived as an opal effect by many people.
- Resins and plastic
The second fake opal group is represented by resins and plastic.
Sometimes man-made plastic with an opalescence effect is marketed under the name “opalite”. The high resin content of these opals changes the physical properties of the material.
Opalite usually has lower specific gravity than natural opal and a lower refractive index. Also, plastic and resins can be identified with a hot metal needle. Needle touch evokes a burnt plastic odor.
Fake Opal made from Assembled Stones
This group is not fake at its classical meaning. There is natural opal but in a very small amount.
Assembled stones are pieces of natural and/or synthetic material fused or glued together in order to enhance the quality of the stone, to protect it, or to increase the weight of the material, and, as a result, to increase value.
We will put assembled or composite stones into the fakes list because such types of opal are usually sold already embedded into the jewelry piece, and sellers prefer not to disclose the truth.
Assembled stones can be divided into two groups. They are doublet and triplet.
A doublet consists of two joined segments. Speaking about fake opal, they are
- Thin low quality dull natural opal and
- Black opaque quartz, chalcedony, black onyx, obsidian, or plastic glued together.
A triplet has three segments. The first two are the same as in the previous example. The third one cabochon or dome, which is overlaying the opal, is made of transparent quartz, glass, plastic, or synthetic corundum. The result is a thin plate of opal enclosed between two segments of non-opal material.
Fake Opals made by treatment
Natural opal porosity makes them good candidates for dye, smoke, and sugar/acid treatments.
The sugar/acid treatment is done by soaking opal for a few days in a warm solution of sugar water, then submerging the opal in sulfuric acid.
The acid oxidizes the sugar in the pore spaces of the opal, producing dark-colored carbon particles and stains. This imparts or darkens a gray, black, or brown body color in the opal.
Synthetic Fake Opals
Another type of fake opal can be described as lab-created, lab-grown, or synthetic opal.
But here it is not fully appropriate to call it fake, because the composition, physical properties, and eventually, the appearance are the same as that of a natural one. So let us just mention lab-created opals here, but thoroughly describe them in a separate paragraph.
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How to Identify Fake Opal?
Fake opal can be identified by color flashes organized in a repeated pattern. Fake opals made of glass can be easily identified by swirls or bubbles inside or conchoidal fracture. Fake opals glued from different materials can be identified when viewed from the side. Synthetic opals have lizard skin texture.
- Fake opal is too shiny. It displays various color flashes organized in a repeated pattern.
- Fake opals made of glass will have swirls and round bubbles inside. Also, they will have a conchoidal fracture
- Fake opals are composed of different plates glued together.
- Fake opals have a columnar structure viewed from the side.
- Fake opals made of plastic produce a burnt plastic odor when touched by the hot metal needle.
How to Tell if Opal is Lab Created
Lab-created (lab-grown) or synthetic opal will have systematically ordered color flashes or lizard skin effect. Synthetic opal has a columnar structure viewed from the side. Synthetic opal is more porous than natural one; it has lower density and does not fluoresce under UV light.
In the 1970s, the Gilson Company developed a three-step process, which generally repeats the natural environment, to make convincing synthetic opal.
- The first is silica spheres precipitation.
- The second is their settle in acidic water for more than a year.
- The third is a consolidation of spheres under a hydrostatic press.
This synthetic opal can be very difficult to identify. If the opal has been created in a laboratory, the pattern will display bright colors in large patches of color.
- The pattern is often ‘too perfect’ and systematically ordered, and can also often display a snakeskin or lizard skin pattern.
- Synthetic opal also has a columnar structure. Viewed from the side, straight columns of color running vertically can be observed. This is the sign of a fake opal.
- One characteristic that distinguishes synthetic opals is that they are much more porous than natural ones.
- Synthetic opals also have lower density compared with real opals, and for this reason, synthetics tend to be lighter.
- Another indication that opal is synthetic is that it does not fluoresce when lit with UV light.
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Real vs. Fake Opal: The Main Differences
The history of fake opals is extremely long. It’s getting harder to distinguish fake opal from a natural one. Here you are welcome to check a table with the main differences between natural and fake opal.
However, we kindly recommend you seek the help of a professional gemologist in case of an expensive purchase.
|Property||Real Opal||Fake Opal|
|Hardness||5,5 — 6,5 the Mohs scale||Plastic and resin-made type of fake opal will have lower hardness: 5 -5,5|
|Play-of-color||Flashes will be organized in random order||Synthetic fake opal will have a uniform repeating pattern and ordered flashes|
|Surface||Real opal will have a smooth surface with random flashes||Lab-grown will have lizard skin or snakeskin effect.|
|Side view||It Will be similar to the front view||Lab-grown: Will have a columnar structure. Assembled stones: Doublet is composed of two different materials triple – composed of three different layers.|
|Presence of black or brown points (soot)||No inclusions should be found in untreated natural opal.||Soot inclusions are a sign of treated natural opal. (Some people do not think it is fake, but this kind of treatment should be disclosed to every person).|
|UV light||Fluorescence||Synthetic opals do not fluoresce under UV light.|
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- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
Natural opals are gemstones of the best appearance and the most intriguing optical effect. Because of the high demand for opals, fakes are extremely widespread.
People usually run into plastics substituents and assembled stones, which are easy to identify with minimum effort. In cases with lab-grown fake opals, it is far more complicated, and it’s always better to ask a professional gemologist‘s assistance.
TIP: Not only opals but also other rare rocks are often sold fake. Therefore, knowing how to distinguish real rocks from fake ones. Find out more about real vs. fake selenite and agate in the articles below: