Cubic Zirconia

Cubic zirconia is zirconium dioxide grown as a crystal in a furnace and cut to diamond proportions. At Mohs 8 to 8.5 it is really hard, above the quartz in household dust at 7, but well below diamond at 10. Its dispersion, the ability to split white light into color, measures around 0.060 against diamond's 0.044, so a CZ actually flashes more rainbow than the stone it imitates.

Density is the other tell, and it changes how the stone is sold. Cubic zirconia is about 1.7 times heavier than diamond for the same volume. A 6.5 millimeter CZ weighs roughly 1.7 carats where a 6.5 millimeter diamond weighs 1.0. Sellers quote millimeter size, or diamond equivalent weight, meaning the carat weight of the diamond it matches in size rather than its own.

What CZ buys is scale without risk. A large stone you can travel with, wear in a crowd and replace for the price of a lunch. What it costs is time. Two or three years of daily wear rounds the facet edges. A film of soap, oil and hand cream builds in the setting until the stone looks gray. Cleaning fixes the film; abraded edges do not come back, so plan to replace rather than restore.

Cubic zirconia is grown by skull melting, a process built around the fact that nothing ordinary can hold the melt. Zirconium oxide powder mixed with a stabilizer, usually yttrium oxide, sits inside a water cooled copper cage. Radio frequency energy heats the center past 2700 degrees Celsius while the outer shell of powder stays solid and acts as its own crucible.

The melt cools slowly over a day or more and columnar crystals grow through it. Those crystals are broken out, sorted, then cut and polished on the same wheels used for gemstones, with proportions copied from diamond brilliant cuts. Adding other oxides during the melt produces colored versions. The whole cycle takes days and uses cheap raw material. A convincing stone costs a few dollars where its natural counterpart costs thousands.