Saturday, 10 December 2016

Diaspore

What is Diaspore or diasporite?

Diaspore, also known as diasporite, empholite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, α-AlO(OH), crystallising in the orthorhombic system and isomorphous with goethite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the luster is markedly pearly in character. It is colourless or greyish-white, yellowish, sometimes violet in colour, and varies from translucent to transparent. It may be readily distinguished from other colourless transparent minerals with a perfect cleavage and pearly luster like mica, talc, brucite, and gypsum by its greater hardness of 6.5 - 7. The specific gravity is 3.4. When heated before the blowpipe it decrepitates violently, breaking up into white pearly scales.
The mineral occurs as an alteration product of corundum or emery and is found in granular limestone and other crystalline rocks. Well-developed crystals are found in the emery deposits of the Urals and at Chester, Massachusetts, and in kaolin at Schemnitz in Hungary. If obtainable in large quantity, it would be of economic importance as a source of aluminium.
Diaspore, along with gibbsite and boehmite, is a major component of the aluminium ore bauxite.
It was first described in 1801 for an occurrence in Mramorsk Zavod, Sverdlovskaya Oblast, Middle Urals, Russia. The name, which was coined by René Just Haüy, is from the Greek for διασπείρειν, to scatter, in allusion to its decrepitation on heating.
Csarite, ottomanite, and zultanite are trade names for gem-quality diaspore (also known as Turkish diaspore) from the İlbir Mountains of southwest Turkey.

History and Occurrence

Diaspore as a mineral has been around since its discovery as a species in 1801, but it wasn't until the 1970's that this mineral was first faceted for gemstone use. From the 1970's through 2005 occasional gems were cut from Diaspore for collectors, but in 2006 this mineral started being mined specifically for gemstone use. Though Diaspore is found in several localities throughout the world, the only source of gemstone material is in a Bauxite deposit in the Anatolian Mountains of central Turkey. Originally exploited for its economic importance for the extraction of aluminium, this deposit is now solely mined for the production of this gemstone.
Diaspore is beautiful and exotic in a soft, subtle manner. It is also one of the lesser known of the colour-change gemstones. Some of the finest examples of gem quality diaspore are found in Turkey's Anatolian Mountains, but it can be found in numerous places around the globe. A rising star in fine jewellery, it's easy to fall in love with its sparklingly brilliant, tranquil earthy colours.

Properties of Diaspore

Chemical FormulaAlO(OH)
ColourRed, Green, Yellow, Pink
Hardness6.5 - 7
Crystal SystemOrthorhombic
Refractive Index1.70 - 1.75
SG3.3 - 3.5
TransparencyTransparent
Double Refraction0.048
LusterVitreous
Cleavage1,2;2,1
Mineral ClassDiaspore