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
Crystal hexagonal crystal system (where the crystals may form hexagons, such as ordinary water ice). Crystals are commonly recognized by their shape, consisting of flat faces with sharp angles. These shape characteristics are not "necessary" for a crystal—a crystal is scientifically defined by its microscopic atomic arrangement, not its macroscopic shape—but the characteristic macroscopic shape is often present and easy to see. Euhedral crystals are those with obvious, well-formed flat faces. Anhedral crystals do not, usually because the crystal is one grain in a polycrystalline solid. The flat faces (also called facets) of a euhedral crystal are oriented in a specific