Zirconium dioxide jewellery. Like diamond, cubic zirconia has a cubic crystal structure and a high index of refraction. Visually discerning a good quality cubic zirconia gem from a diamond is difficult, and most jewellers will have a thermal conductivity tester to identify cubic zirconia by its low thermal conductivity (diamond is a very good thermal conductor). This state of zirconia is commonly called "cubic zirconia", "CZ", or "zircon" by jewellers, but the last name is not chemically accurate. Zircon is actually the mineral name for naturally occurring zirconium silicate (ZrSiO). Zirconium dioxide Zirconium dioxide (), sometimes known as zirconia (not to be
Centenary Diamond initial efforts were done by head rather than with a hand or saw so as not to heat or vibrate the diamond. After cutting and removing of cracked material over 154 days, the team was left with an egg-shaped gem of approximately . Thirteen different designs were presented to the De Beers board, with a strong recommendation for what became the eventual modified heart-shaped design. The shape was described as, "Effectively, the Centenary Diamond is shaped like a heart-shape, but it does not have a groove. The image the team had in mind was a shape which would adorn the