Diaspore

Diaspore is an aluminium oxide hydroxide mineral with the chemical formula a-AlO(OH). It often occurs in lamellar form (thin plates or scales) but sometimes also forms crystals such as the ones shown in the images.

Diaspore
From Mugla Province, Aegean Region, Turkey.
Size 1.8 x 0.6 x 0.4 cm
Photo by Rob Lavinsky, iRocks.com
- image lic. under CC-BY-SA-3.0

These crystals as sometimes used as gemstones - however much of the diaspore found is not of gem quality. Diaspore is a component of bauxite - an aluminium ore used industrially to obtain aluminium. Diaspore has also been called empholite, kayserite or tanatarite. [1]

Another set of gemstones that are formed from an aluminium oxide is the corundum stones - sapphire and ruby, which are composed of Al2O3. However, these stones are quite different from diaspore.

Diaspore is isomorphous with goethite - meaning that it has the same or fundamentally the same crystal shape. It also has the interesting quality of making crystal "twins" that are heart-shaped or "fishtail" shaped in cross section. Diaspore has perfect cleavage in one direction - and it is said that this is a major reason why it is one of the most difficult gemstones to facet. [2]

Diaspore Color Change

Diaspore also sometimes has the unusual quality of exhibiting a color change effect under different forms of light. The stone itself can occur in colors amber, white, brown, colourless, pale yellow, greyish, lilac, violet, pinkish [1] [3] - however under varied light conditions it can show color change between the green and red spectra. The color change characteristic is stronger in larger stones. A similar color change phenomenon can also be seen in the stone alexandrite.

As with alexandrite, the diaspore color change is considered a highly desirable gemstone quality which can lead to greatly increased prices at retail. Diaspores with good clarity, color and color change characteristic can command high cost: Looking around online (August 2010), I just saw a 4.68 carat diaspore priced at $4680 ($1000 per carat.) However, smaller stones with lesser or no color change can be seen at much lower prices, and I have seen a 1.99 carat stone priced at $70.

I have read that care should be taken when buying color-change diaspore online; as it has been known for photos to be altered to show color change. [2]

The world's main source for gem quality diaspore is Turkey. [2] The stone has also been found in several other locations worldwide - including in Antarctica, Australia, Austria, Brazil, Bulgaria, Canada, Chile, China, Czech Republic, France, Greece and Japan. [3]

Diaspore - Sources Referenced:

[1] http://en.wikipedia.org/wiki/Diaspore
[2] http://www.atggems.com/Photos_Diaspore.htm
[3] http://www.mindat.org/min-1285.html

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