Diaspore

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Diaspore
Chemical composition AlO(OH)
Crystal system Orthorhombic
Habit Tabular, sometimes fibrous
Cleavage Perfect to imperfect
Fracture Conchoidal
Luster Bright vitreous to pearly (on cleavage surface).
Hardness 6.5 - 7
Optic nature Biaxial +
Refractive index 1.682 - 1.752
Birefringence 0.040 - 0.048
Specific gravity 3.2 - 3.5
Lustre Vitreous
Pleochroism Moderate
Color-changing diaspore from green in daylight to brown in incandescent light - also known as “Zultanite” in the gem market.
Photo courtesy of Chaman Golecha, Gem Testing Laboratory, Jaipur.


Diaspore as a plausible gemstone has been reported first around 1977 when a large enough crystal was examined at the Gem Testing Laboratory in London. This, usually colorless, material showed good color-change from pale bluish-green to pale pinkish-brown. Turkey was the origin of this color-change material. When Zultanite Gems LLC aquired the mining location, this color-change variety of diaspore was marketed under the tradename "zultanite®". At present (2007) sole distribution rights of "zultanite®" are granted to GemsTV.