With new gem finds constantly in the news and gemstone treatments becoming increasingly sophisticated, it's a challenge these days to determine whether a gem's color occurs naturally or as the result of an enhancement. Tough as that may be, it shouldn't overshadow the even more important detective work you need to do: distinguishing synthetics from natural gems. John Koivula, the Gemological Institute of America's chief research gemologist and an expert in visual identification of gemstones, has helped us compile a list of the top 10 man-made gems you should be on the lookout for.
How did we choose our top 10? It wasn't easy. With the laser industry creating gem materials by the ton, there are huge numbers of synthetics on the market today. To limit our list to the most appropriate gems, we used three criteria: (1) All of them look like natural stones. (2) They all are readily available to the trade. We saw little sense in discussing a gemstone if there's little probability you will see it in your store. (3) You can identify the gems without sending them off to a laboratory for analysis. The gems you're most likely to encounter are at the top of the list.
Of course, the more you understand how synthetics are created, the easier it is to identify their telltale characteristics. Each manufacturing process creates certain trademark inclusions. The marks inside a Czochralski pulled gem, for example, are totally different from those inside a flux-grown product.
Advances in technology can throw you off, however. The old flame fusion synthetic process, for instance, leaves very visible curved growth, which sometimes can be seen even by the unaided eye, especially in larger stones. But newer hydrothermally processed gem materials show only slight indications that the gem was lab-created. Since nature also creates gemstones in a hydrothermal environment, the internal growth structures in synthetic gems produced by this process appear very similar to those in natural gems. While this top 10 list will help you spot some synthetics, you're bound to encounter situations in which it's best to let a laboratory make the determination.1. Amethyst
The synthetic gem you are most likely to see and need to identify is amethyst. One might think that the more expensive synthetics would be more difficult to identify, but synthetic amethyst, at only $6 per carat, is probably the toughest. With few or no inclusions to examine, and at such a low cost, how much time do you want to spend sitting at the microscope trying to identify man-made imposters? If you want to save the expense of sending amethyst to the lab for identification, the best advice is to buy gems with inclusions. You'll be able to identify them—and maybe your customer will appreciate all the trouble you've gone through to guarantee that her stone is natural.2. Ametrine
Ametrine, a combination of citrine and amethyst, originates naturally from Bolivia; material that originates from Brazil is heat-treated. Synthetically, it is produced in hydrothermal laboratories. Even though your customers may not be lining up to ask for ametrine, synthetic manufacturers are growing it.3. Synthetic Moissanite
All you need to do to identify this diamond substitute is look inside it. Groups of long, thin, and somewhat wavy needle-like inclusions are very common in moissanite—not at all in diamond. Synthetic moissanite is created in the hexagonal crystal system, which means it's doubly refractive (you see two of everything when you look through to the other side of the gem). Just look into a number of bezel facets to the culet. If you see two culets, chances are very good you've got moissanite! (Note, however, that very slight doubling is present in colorless sapphire, another diamond substitute.)4. Emerald
Because emerald and ruby are so valuable, it's important that you learn to distinguish the natural from the synthetic. Emeralds are grown by the flux and hydrothermal methods. Both create gems that are dead-ringers for the natural thing. Inside the flux-grown synthetics, you will find white fingerprints of flux as well as platinum platelets. In the hydrothermally grown synthetics, you should look for graining, as with other hydrothermally grown gems, but you may also find small, angular, nail-shaped spikes. The head of the “nail,” a crystal of some sort, blocks the direction of crystal growth, which creates the spike portion of the nail.5. Ruby
As is the case with emerald, it's important to know how to identify natural from synthetic ruby because of the dollars at stake. The extraordinary thing about synthetic rubies is that you are bound to find one or more in original art deco jewelry. The creation of a synthetic gem was a technical marvel back then, not a way to achieve more affordable gems. To match 30 or 40 “Burma” color rubies, synthetics were commonly combined with naturals. Gas bubbles and curved striae will be obvious in synthetic rubies found in art deco pieces. Created rubies from later in the 20th century have more subtle gas bubbles and striae.
Flux rubies were created in the latter half of the century. They show white “fluxy” fingerprints and platinum triangular platelets, similar to those seen in other flux-created gems. Platinum is less apparent in the newer product. In Ramaura synthetic ruby, the created ruby begins its growth suspended in the melt instead of starting from a “seed crystal” at the bottom of the crucible. The resulting ruby shows fewer flux inclusions but some unusual angular graining. It is very difficult to make identifications based solely on wavy angular graining patterns. That's why, when identifying the Ramauras and the latest hydrothermal synthetic rubies, you must be absolutely sure before you make the call.
Curved striae are highly characteristic of synthetic rubies grown by the flame-fusion process. Deposits of successive flow layers create the pattern we associate with this synthetic. 15x.
Both primary and secondary flux inclusions are visible in this flux-grown synthetic ruby. Such inclusions are generally considered to be proof of synthesis in rubies. The heat treatment of natural rubies, however, can create some similar internal patterns, thereby clouding the issue. 20x.6. Sapphire
When you examine a sapphire, you're more likely to be looking for evidence of heat treatment than determining origin. Most synthetic sapphire is colorless. Crank up the magnification and look for tiny white clusters of pinpoints. These are gas bubbles in the synthetic, grown by the flame-fusion method. Blue flame-fusion synthetics are easier to identify; look for curved colored growth rings. Place a facial tissue over the well of your microscope to diffuse the light when searching for the blue bands of color. Gas bubbles will appear almost black. Synthetic flux sapphires usually contain drippy flux fingerprints. While heat-treated natural ruby may show something similar, natural sapphires are not commonly heated to temperatures as high as those used to heat-treat rubies. Therefore, visible fluxy fingerprints are a strong indication that the stone is synthetic.
This platinum platelet in a flux-grown sapphire shows skeletal development on one edge, which results from rapid growth and a diminishing supply of needed platinum. The metallic gray luster and color of the platinum inclusion are also visible in this photomicrograph. 40x.7. Alexandrite
If you deal in rare gems, you need to be able to identify alexandrite, known for its dramatic color change. If you're familiar enough with natural “alex,” you could almost identify the gem based on the colors of change. But since there are so many color-change gems—both natural and synthetic—on the market today, it's best to look inside the gem for natural, hydrothermal, or flux inclusions rather than try to make sight identifications.8. Aquamarine
Since aquamarine is easily simulated by topaz, glass, and synthetic spinel, you might not think it would be synthesized. But with the price of the natural gem now exceeding $50 per carat, inexpensive lab-created aquas could be a reasonable alternative for some customers. To make the identification, you need to understand that aquamarine, unlike its beryl family relative, the emerald, is commonly found in large, inclusion-free crystals. Therefore, to distinguish natural from synthetic aquamarine, you need to be keenly aware of what inclusions—if any—might appear in the lab-created gem. Synthetic aquas, grown via the hydrothermal process, show unusual wavy growth zones, which can best be seen using darkfield binocular illumination.9. Spinel
It used to be that the spinel you carried in the store was automatically considered to be synthetic and inexpensive, most commonly a center stone in a high school class ring or mother's pin. Nowadays, though, because demand for natural red flame spinel is so great, you must be prepared to examine spinels for two different synthetic possibilities: flame fusion and flux.
Flame-fusion spinel, if colored, can be identified quite readily; the characteristic gas bubbles and curved growth markings are usually fairly obvious at 10x. Identifying colorless spinel is much more difficult, since the bubbles usually appear simply as tiny white dots, and the curved growth is transparent. With determination—and a little higher magnification in a darkened room—you should be able to make the identification.
Flux synthetic spinel is a much more difficult call. Just knowing that flux-processed spinels can show angular growth and few inclusions, if any at all, can keep you from making any hurried “natural” identifications. Look for fingerprints of tiny octahedral crystals (“double pyramids”) in the natural gem.
A trail of primary flux inclusions serves to identify its host as a flux-grown synthetic red spinel. Without inclusions like this, the separation of natural from synthetic can prove to be troublesome and much more time-consuming. 15x.10. Opal
Both black and white opals can be created in the lab. The white opal looks much more like the real thing, though, so be extra careful here. The synthetic process is a form of sedimentary event, which is quite similar to the way that natural opals are formed. The telltale inclusions in the synthetics are columns of color and a snakeskin/chicken wire/honeycomb-like pattern. Immersing the opal in water seems to help reduce the glare of light reflecting off the surface, allowing you to see the synthetic structures more clearly. Don't use magnification that is too strong. You can be too close to the trees to see the forest.
Do use generous amounts of patience. It's not as easy as it sounds. Don't confuse the chicken-wire effect with natural harlequin color patchwork. And don't assume that the gem you see is opal simply because it looks like opal. There are plastic imitations that can duplicate the white opal appearance, and, of course, show no synthetic patterns. Plastic has a higher refractive index than the real thing.
The more you understand how synthetics are created, the easier it is to identify their telltale characteristics.