Diamond has been imitated since the early 1900s. The imitations fall into two distinct categories: synthetic diamond and diamond simulant. Synthetic diamonds possess the same characteristics as naturally occurring diamonds, but are grown in a laboratory (man made diamonds). A diamond simulant possesses a different chemical composition, but is very diamond-like in appearance.
Diamond simulants can be composed of natural or artificial elements, or a combination of both. The most common simulants are rhinestones (high-leaded glass) and cubic zirconia (zirconium oxide, ZrO2), both of which are artificially created. Moissanite (silicon carbide, SiC), though first discovered in 1893, is a recent entry into the diamond simulant market, becoming popular in the late 1990s.
To properly imitate their natural counterparts, diamond simulants must contain certain diamond-like properties. Hardness and durability top the list. For use in jewelry and in technology these stones must resist scratches and effects of contact with other objects. Few simulants are as hard as a diamond, which rates a perfect 10 on the Mohs scale of mineral hardness. Moissanite comes the closest, measuring 9.5. Cubic zirconia, certainly the most popular simulant, is softer, falling into a range of 8-8.5.
Diamond simulants must also display certain optic and color characteristics. Diamonds contain a high refractive index (RI), the measure of how much light bends upon entering the stone. The dispersion factor, degree that white light is split into spectral--rainbow--colors, is also important. These two measurements are commonly referred to as brilliance and fire. Too low an RI and the diamond simulant will appear lifeless. Too high and the stone looks unreal. Color refers to how "white" (colorless) the stone appears. Most simulants are completely colorless, and are usually flawless as well, adding greatly to their brilliance, fire, and popularity.
Natural diamond simulants, minerals that when cut optically resemble white diamonds, are rare. The most notable is zircon (not to be confused with zirconium oxide). Mined in Sri Lanka for over 2000 years, colorless zircon, before modern mineralogy, was thought to be an inferior diamond. Called Matara, after its geographic source, zircon is still found today. Other natural simulants include crystal, topaz and beryl, but all contain so many impurities that mass production isn't feasible. As a result, the majority of diamond simulants are artificially created.
The first artificial diamond simulant, synthetic white sapphire (Al2O3, pure corundum), was produced in the early 1900s . Rating a 9 on the Mohs hardness scale, synthetic white sapphires are sadly much lower in RI. When cut, the stones appear lifeless, lacking diamond's brilliance and fire. Still, the white sapphire, marketed as Diamondette, Diamondite, Jourado Diamond and Thrilliant, was popular until the late 1940s when better simulants emerged onto the market.
The first of these so-called "better" diamond simulants was synthetic rutile (TiO2, pure titanium oxide), introduced in 1947-48. Unlike white sapphire, rutile possessed a lot of brilliance when cut, almost opal-like in it's prism display of color. Unfortunately, the synthetic rutile also contained an undeniable yellow tint, and rated a mere 6 on the Mohs scale. Synthetic rutile was marketed by several commercial names, including Diamothyst, Rainbow Diamond, and Ultamite.
Possibly the best diamond simulant during the 1940s and 1950s was strontium titanate (SrTiO3, pure tausonite). Strontium titanate possessed superior optics, with an RI close to diamond, a very high dispersion rate; and completely lacked the yellow tint of rutile. Still softer than diamond with Mohs rating of 5.5, strontium titanate was combined with more durable materials to create composites. At peak production, 1.5 million carats (300 kg) were produced annually, marketed under names including Brilliante, Fabulite, and Marvelite.
During 1970-1976, a new class of diamond imitations, synthetic garnets, began to steal strontium titanate's thunder. Unlike other diamond simulants, synthetic garnets do not have a counterpart in nature, composed of oxides rather than silicates, and of some uncommon rare earth elements. Only two of the types of synthetic garnets grown were important as diamond simulants. The first, ytrrium aluminum garnets (YAG, Y3Al25O12), emerged in the late 1960s and are still produced. YAG was extremely pure, rated an 8.25 on Mohs scale and possessed a decent RI and dispersion rate. Commercially marketed as Diamonique and Replique, YAG peaked at an annual production of 40 million carats (8,000 kg) in 1972.
The second synthetic garnet used as a diamond simulant was gadolinium gallium garnet (GGG, Gd3Ga5O12). Similar to YAG, GGG rated a 7 on Mohs, but had a dispersion factor and an RI much closer to that of natural diamond. Unfortunately, GGGs cost much more to produce, and had a tendency to turn brown when exposed to sunlight. Marketed as Diamonique II and Galliant, GGG was never produced in significant quantities and pretty much dropped out of sight by the close of the 1970s.
In 1976, cubic zirconia (CZ) (ZrO2, zirconium oxide) burst onto the scene and is still the most gemologically and economically important diamond simulant. Produced as a result of the invention of microwave technology, CZ hit the market as a colorless, flawless gemstone and quickly dominated the industry. The hardness for CZ is measured as a range of 8-8.5, because stabilizers have to be added the production process. CZ's RI and dispersion factor can also be affected by the stabilizers, but on average CZ possesses near-diamond brilliance and fire. Cubic zirconia is also inexpensive to produce, adding to its popularity.
In 1998, moissanite (SiC; synthetic silicon carbide) became available, challenging CZ's popularity. Rating a 9.5 on Mohs scale, moissanite is more resistant to heat, making it easier to set in molten gold. Currently produced by only one company, Charles and Colvard, moissanite is less readily obtained and therefore much more expensive than CZ.
Clearly, the perfect diamond substitute has yet to be discovered and/or developed. As technology improves, however, it is only a matter of time until the "best" alternative is found.
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