In 1937, German mineralogists discovered the natural mineral form of the gemstone in a single site. It has never been found in nature again.
Cubic zirconia, also called CZ, is a synthetic crystalline substance used as an affordable alternative to diamonds. Cubic zirconia is not a mineral; it is a man-made substance. The current synthetic version of cubic zirconia is a crystalline form of the metallic element zirconium dioxide. It was first produced in a laboratory in 1977. Cubic zirconia crystals are made by melting powdered zirconium and zirconium dioxide together by heating them up to 4,982ºF.
Unlike diamonds, cubic zirconia is simulated to be flawless. CZ can be perfectly structured, free of inclusions, totally transparent and possess a brighter fire. Cubic zirconia has is own grading scale to measure quality. Like other gemstones, cut, size and shape influence how light is refracted and will affect the stone's brilliance.
A colorless cubic zirconia is extremely difficult to distinguish from a diamond, and appears identical to the untrained eye. Diamonds are the hardest gemstone in the world, a 10 on the Mohs scale of hardness. Cubic zirconia is softer, but still considered a hard gemstone with an 8.5 rating. The denseness of cubic zirconia makes it about 75% heavier than diamonds. Cubic zirconia tends to contain more flashes of color than the typical diamond. CZ's very high refractive index and transparency mimic the look of the most expensive diamonds in clarity and brilliance. Cubic zirconia does not have cleavages, making them less brittle and susceptible to chips and cracks than diamonds.
(All information shared from HSN.com)