Cubic Zirconia (or synthetic cubic zirconia, as proper term re GIA's classification) is an incredible material. It is definitely a "gem" in its own right and for all its physical, chemical, and optical properties that have stood the test of time, it is still the best "diamond simulant" ever created.
Baddeleyite is a natural mineral of the same chemical composition, but it is a monoclinic mineral. If the mineral is heated to about 2300 degrees Celcius, it becomes isometric. In this form it is unstable, and on cooling, it reverts back into the original form. In the synthetic, this reversion is overcome by adding up to 15 % of an oxide as a stabilizer. Yttrium, calcium, and others can be used. The added stabilizer evidently contributes to some variation. Almost all the rough in the market are chemically comprised of zirconium oxide and yttrium oxide. Individually, both of these materials are opaque, white ores, but when melted together under appropriate conditions, they combine to form an amazingly brilliant, clear crystal.
Producing cubic zirconia is an art in itself. The extremely high temperature required to melt the ores (almost 5,000 degrees Fahrenheit) is too hot for any conventional crucible, or melting vessel, to withstand. Therefore, to produce cubic zirconia, scientists have devised a proprietary process. A radio-frequency "skull crucible" system is used, in which the melting zirconia powder actually creates the sides of its own container during its formation. Cooling this extremely hot molten ore becomes the most crucial step in the entire process. A carefully programmed cooling procedure is required to form the flawless crystals that are subsequently transformed into exquisite cubic zirconia gemstones.
Like diamonds, the best cubic zirconia gems are colorless (or white, as most people describe their colors) and do not lose their color or brilliance. Given proper cleaning, the cubic zirconia will retain its own flawless, radiant beauty permanently, just as the diamond does. To fulfill the jewelers' need for colors besides the unbeatable brilliancy, manufacturers also produce colored cubic zirconia. It is available in a variety of colors. Cubic zirconia gemstones are cut in the same fashion as diamonds. The size of the gemstone is usually indicated by its weight in carats, a carat being one-fifth (1/5 ) of a gram. The stone can also be measured in millimeter diameter size.
Because the cubic zirconia stone is so dense and solid, it outweighs a diamond of the same millimeter size, weighing 1.7 times more than a diamond of the same millimeter diameter. The best cleaning agent for cubic zirconia is liquid dishwashing detergent. However, other gems and jewelry cleaners can also be used. Natural skin oils, soap, and dirt cause a film that dulls the beauty and luster of the cubic zirconia, just as it dulls real diamonds.
Hardness (Mohs' scale)
between 5.65 - 5.95