High quality, large alexandrite specimens are rare and expensive, and therefore this is a gem that has inspired imitations and synthetics. Alexandrite was successfully synthesized by 1973 and it is often imitated by synthetic corundum and synthetic spinel. The hardness is 8.5 and specific gravity 3.70-3.78. It has good cleavage and falls within the orthorhombic crystal system. The transparency varies from transparent to opaque and it is doubly refractive, 1.746 and 1.763.
Fluorescence is weak to none.
The host rock for chrysoberyl is granite pegmatite, metamorphic schists, and secondary placer deposits. The flawless Hope chrysoberyl is a light green faceted stone of 45 carats on display in London. Amethyst Rough amethyst taken from Gallery of Gems Amethyst is a purple, crystalline variety, of quartz, SiO 2 . It has a hardness of 7 and average specific gravity at 2.65. The fracture is conchoidal and there is no cleavage.