Zirconia is one of the most commonly used gemstones. The zirconia is an imitation of the diamond, which not only looks deceptively similar to it, but also has a great hardness itself. When a zirconia is fully cut, it resembles a brilliant-cut diamond in every detail. Chemically speaking, zirconia is a synthetically produced single crystal obtained from zirconium-4-oxide. Since zirconia has an immense hardness (8-8.5 on the Mohs scale) at low manufacturing costs and also looks like a diamond or brilliant, it has become an optimal gemstone replacement in jewellery production and has completely replaced the previously used rock crystal. Zirconia stones can be produced in any conceivable size and shape and cost a thousandth of a comparable diamond of similar purity. Even if jewellers take a closer look at the stone, there can be no clear distinction between zirconia and diamond. Only when the thermal conductivity value is consulted does the difference become apparent: diamonds conduct higher temperatures extremely well, zirconia very badly. Zirconia is found in many pieces of jewellery, whether rings, necklaces, pendants or earrings, and offers diamond optics and absolute high quality at a relatively low price.