Tuesday, 27 December 2016

Chrysoberyl - Alexandrite

Chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones. Chrysoberyl is the third-hardest frequently encountered natural gemstone.

The three main varieties are ordinary yellow-to-green chrysoberyl, cymophane (cat's eye), and alexandrite.
Cymophane exhibits chatoyancy or opalescence that appears very much like an eye of a cat. When cut to cabochon, the mineral forms a silky band of light extending across the surface of the stone.

Microscopic tubelike cavities or needlelike inclusions of rutile are orientated parallel to the c-axis producing the chatoyant effect.

Alexandrite undergoes dramatic shifts in color depending on what kind of light it's in. A variety of Chrysoberyl, alexandrite's color-changing properties is due to an exceedingly rare combination of minerals that includes titanium, iron and chromium. Originally discovered in Russia’s Ural Mountains in the 1830s, it’s now found in Sri Lanka, East Africa, and Brazil.
Fine, gem quality material is exceptionally rare and valuable. Alexandrite's mohs hardness is about 8.5.