Diamond Simulant
Diamonds have 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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