Cubic Zirconia Or CZ, the cubic crystalline form of zirconium dioxide (ZrO2), is a mineral that is widely synthesised for use as a diamond simulant. It is hard, optically flawless and usually colourless, but may be made in a variety of different colours. Although it does occur, Cubic zirconia is extremely rare in nature.
Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important diamond simulant since it first became commercially available in 1976. Its introduction caused some panic in diamond marketing circles in that it really is a very good diamond mimic. It is even almost as hard as diamond.
More recently brilliantly coloured CZ's have been available in the last few years and they make a powerful addition if you like your big bling to come without a big bill. Its main competition as a synthetic gemstone is the more recently discovered material, synthetic moissanite.