Cubic zirconia is the crystalline form of zirconium dioxide ZrO2
As its name suggests,
cubic zirconia's crystal system is composed of cube-shaped unit cells. This is
one of the most common shapes found in metallic crystals. Under ultra violet light,
cubic zirconia emits yellow / greenish yellow fluorescence.
Moissanite is the crystalline form of silicon carbide SiC. Under ultra violet light, moissanite emits a a very slight green, yellow, or gray fluorescence.
Today's cubic zirconia has virtually no inclusions and is near flawless. All moissanite jewels
contain inclusions, comparable to diamonds of VS1 clarity.
Unlike cubic zirconia, moissanite jewels are doubly refractive. This means that light is bent twice as it
passes through the moissanite jewel. This double refraction is directly responsible for
moissanite's superior brilliance. You can see this with a 10x loupe. Viewing through the crown
or pavilion facets is recommended. Do not look directly through the table of a moissanite
stone; the double refraction is less apparent as seen from this angle.