Diamond has been imitated by artificial materials for hundreds of years: advances in technology have seen the development of increasingly better simulants with properties ever nearer those of diamond. Although most of these simulants were characteristic of a certain time period, their large production volumes ensured that all continue to be encountered with varying frequency in jewelry of the present.
Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most common & economically important competitor for diamonds since commercial production began in 1976."
It is a dense substance, with a specific gravity between 5.6 and 6.0 at least 1.6 times that of diamond. Cubic zirconia is relatively hard, at about 8 on the Mohs scale slightly harder than most semi-precious natural gems. Its refractive index is high at 2.15 to 2.18 (compared to 2.42 for diamonds) and its luster is adamantine. Its dispersion is very high at 0.058 to 0.066, exceeding that of diamond (0.044)."
Under shortwave UV cubic zirconia typically fluoresces a yellow, greenish yellow or "beige". Under longwave UV the effect is greatly diminished, with a whitish glow sometimes being seen. Colored stones may show a strong, complex rare earth absorption spectrum.
Because the natural form of cubic zirconia is so rare, all cubic zirconia used in jewelry has been synthesized, or created by humans.
What is a Synthetic Diamond Simulant ?
In order to be considered for use as a diamond simulant, a material must possess certain diamond-like properties. The most advanced artificial simulants have properties which closely approach diamond, but all simulants have one or more features that clearly and (for those familiar with diamond) easily differentiate them from diamond.
To a gemologist, the most important of differential properties are those that foster non-destructive testing, and most of these are visual in nature. Non-destructive testing is preferred because most suspected diamonds are already cut into gemstones and set in jewelry, and if a destructive test (which mostly relies on the relative fragility and softness of non-diamonds) fails it may damage the simulant—this is not an acceptable outcome for most jewelry owners, as even if a stone is not a diamond it may still be of value.
Following are some of the properties by which diamond and its simulants can be compared and contrasted."
Durability & Density
The Mohs scale of mineral hardness is a non-linear scale of common minerals' resistances to scratching. Diamond is at the top of this scale (hardness 10) as it is one of the hardest naturally-occurring materials known."
"In the recent past, the so-called "window pane test" was commonly thought to be an assured method of identifying diamond." "Hardness tests are inadvisable for three reasons: glass is fairly soft (typically 6 or below) and can be scratched by a large number of materials (including many simulants); diamond has four directions of perfect and easy cleavage (planes of structural weakness along which the diamond could split) which could be triggered by the testing process; and many diamond-like gemstones (including older simulants) are valuable in their own right.
Diamonds are usually cut into brilliants to bring out their brilliance, the amount of light reflected back to the viewer, and fire, the degree of colorful prismatic flashes seen. Both properties are strongly affected by the cut of the stone, but they are a function of diamond's high refractive index (RI; the degree to which incident light is bent upon entering the stone) of 2.417 (as measured by sodium light, 589.3 nm) and high dispersion (the degree to which white light is split into its spectral colors within the stone) of 0.044, as measured by the sodium B and G line interval. Thus, if a diamond simulant's RI and dispersion are too low it will appear comparatively dull or "lifeless"; if the RI and dispersion are too high, the effect will be considered unreal or even tacky.
Equally important is optic character. Diamond and other cubic materials like cubic zirconia are isotropic, meaning light entering a stone behaves the same way regardless of direction. Conversely, most minerals are anisotropic which produces birefringence or double refraction of light entering the material in all directions.