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
Diamond clarity Diamond clarity Diamond clarity is the quality of diamonds that relates to the existence and visual appearance of internal characteristics of a diamond called "inclusions", and surface defects, called "blemishes". Clarity is one of the four Cs of diamond grading, the others being carat, color, and cut. Inclusions are solids, liquids, or gases that were trapped in a mineral as it formed. They may be crystals of a foreign material or even another diamond crystal, or may have produced structural imperfections, such as tiny cracks that make a diamond appear whitish or cloudy. The number, size, color, relative location, orientation,