Cubic Zirconia

Cubic Zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). CZ is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, however may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4), a much more expensive jewel partly because it is so rare.

Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemological and economical competitor for diamonds since commercial production began in 1976. Its main competitor as a synthetic gemstone is a more recently cultivated material, synthetic moissanite.

Cubic Zirconia (CZ) vs. Diamond

There are a few key features of cubic zirconia which distinguish it from diamond:

  • Hardness: CZ has a rating of approximately 8 on Mohs hardness scale a rating of 10 for diamond. This causes sharp edges in cut crystals to dull and rounds off in CZ, while with a diamond the edges remain sharp. Furthermore, when polished, a diamond will rarely show polish marks and those seen will travel in different directions on adjoining facets while CZ will show polishing marks along the same direction of the polish.
  • Specific gravity: the density of CZ is about 1.7 times that of a diamond. This difference allows skilled gem identifiers to tell the difference between the two by weight. This property can also be exploited by dropping the stones in heavy liquids and compare their relative sink times (diamond will sink more slowly than CZ).
  • Refractive index: CZ has a refractive index of 2.15–2.18, compared to a diamond's 2.42. This led to the development of immersion techniques of identification. In this method, stones with refractive indices higher than that of the liquid used will have dark borders around the girdle and light facet edges while those with indices lower than the liquid will have light borders around the girdle and dark facet junctions.
  • Dispersion is very high at 0.058–0.066, exceeding a diamond's 0.044.
  • Cut: CZ gemstones may be cut differently from diamonds. The facet edges can be rounded or "smooth".
  • Color: only the rarest of diamonds are truly colorless, most having a tinge of yellow or brown to some extent. Cubic Zirconia is often entirely colorless: equivalent to a perfect "D" on diamond's color grading scale. Other desirable colors of cubic zirconia can be produced including near colorless, yellow, pink, purple, green, and even multicolored.
  • Thermal conductivity: Cubic zirconia is a thermal insulator whereas diamond is the most powerful thermal conductor. This provided the basis for Wenckus’ identification method (currently the most successful identification method)