CUBIC ZIRCONIA - In its mineral form, Cubic Zirconium, or CZ is very rare, however, it can be synthesised in a laboratory to simulate diamonds. Virtually indistinguishable from diamond with the naked eye, CZ has a hardness of 8.5 on the Mohs scale compared to a diamond at 10. It is also 75% heavier. Visually flawless and colourless, Cubic Zirconia can be mixed with various oxides to create colour.