Cubic zirconia
(or CZ), the cubic crystalline form of zirconium dioxide (ZrO2),
is a mineral that is widely synthesized for use as a diamond
simulant. The synthesized material is hard, optically flawless
and usually colorless, but may be made in a variety of different
colors.
Because of its durability, and close visual likeness to natural
diamonds, synthetic cubic zirconia has remained the most
gemologically and economically important diamond simulant since
1976.