But this is a slow and complicated process taking thousands of years if it happens at all. It is a slow process mostly because the transformation involves the breaking of bonds and the rearrangement of atoms. Atoms of aluminum and sodium in the structure may help the stability of cristobalite as well. Color is colorless or white. Luster is vitreous.
Crystals are transparent to translucent.
The crystals are typically pseudo-octahedrons, some of which are twinned in a special twin called the spinel twin . The more commonly observed habit is radiating clusters and spherical aggregates. Cleavage is absent. Fracture is conchoidal. Streak is clear.