Cubic Zirconia

Cubic Zirconia is zirconium oxide (ZrO₂), a mineral that is extremely rare in nature, but is widely synthesized for use as a diamond simulant. The synthesized material is hard, optically flawless and usually colourless, but may be made in a variety of different colours. It should not be confused with zircon, a zirconium silicate (ZrSiO₄).

Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important diamond simulant since 1976. Its main competition as a synthetic gemstone is the more recently cultivated material moissanite.

It is a dense substance, with a specific gravity of between 5.6-6.0. Cubic zirconia is relatively hard, at about 8.5 on the Mohs scale - nowhere near diamond, but much harder than most natural gems. Its refractive index is high at 2.15-2.18 (B-G interval) and its lustre is subadamantine. Its dispersion is very high at 0.058-0.066, exceeding that of diamond (0.044). Cubic zirconia has no cleavage and exhibits a conchoidal fracture. It is considered brittle.

In recent years manufacturers have sought ways of distinguishing their product by supposedly "improving" cubic zirconia. Coating finished pieces in a film of diamond-like carbon (DLC) is one such innovation, a process using vapour deposition. The resulting material is purportedly harder, more lustrous and more like diamond overall: The coating is thought to quench the excess fire of cubic zirconia, bringing it in line with diamond.

Another technique first applied to quartz and topaz has also been adapted to cubic zirconia: Vacuum-sputtering an extremely thin layer of metal oxide (typically gold) onto the finished stones creates an iridescent effect. This material is marketed as "Mystic" by many dealers. Unlike DLC, the surreal effect is not permanent, as abrasion easily removes the oxide layer.