CZ nearly always refers to synthetic man made cubic zirconia, but it also occurs naturally, natural cz is very rare.
Synthetic CZ is made by heating zirconium oxide powder up to nearly 5000'F. Because it is so hot the powder
needs to be heated from the centre outwards by radio waves so that the outer powder which is cooled by copper
water pipes forms a crucible to contain it. As the mixture cools cz crystals grow. The zirconium oxide powder needs stabilisers and needs to be cooled carefully, the right balance of stabiliser and careful cooling determine the
quality of the cubic zirconia.

The best quality crystals are flawless and are 8.5mohs in hardness. Lesser quality cubic zirconia is not so hard
and may have small bubbles that implode and cause the stone to discolour over time, this doesn't happen with
high quality cz. Because of its hardness it will last a long time, below is the mohs hardness scale, anything on the
list can cut something with a lower number, but that item with the lower number cannot even scratch the surface of something with a higher number. You can rub cz with sandpaper (not wet and dry) and it doesn't scratch.

The hardness of quartz is important to a gemstones lifetime. Quartz is all around us in dust and scratches the
surface of any item which is less than 7 mohs of hardness which includes any gemstones less than 7 mohs
which are in your jewellery. Cubic Zirconia is 8.5 mohs so is never affected by quartz.

1 Talc
2 Gypsum
2.5 to 3 pure Gold
3 Copper
4 Flurite
4.5 Platinum
5 Iron
6 Titanium
7 Glass
7 Quartz
7 to 8 Hardened Steel
7 to 8 Sandpaper
8.5 Cubic Zirconia
9 Emery Cloth, Corundum, (sapphire, rubies, scratch proof glass on watches)
9.25 Moissanite
9.5 Sintered diamond tools such as diamond coated drill pieces and files.
10 Diamond