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Friday, June 28, 2013

Taaffeite - a very rare stone

 - pronounced TAR-fite, first discovered by Edward Taaffe when searching through a box of spinels (1945)
- a very rare beryllium magnesium aluminum oxide gemstone found today in Sri Lanka, Burma, Madagascar and Tanzania

Is it a variety of spinel?
- most certainly not, Red Taaffeite is FAR MORE RARE than red beryl (bixbite). Red beryl has an RI (refractive index) of 1.564 to 1.602 and a SG of 2.70. Taaffeite has an RI of about 1.72 to 1.78 and an SG of 3.60 to 3.61. Differentiating the two is very basic gemology. It also shows a distinct double refraction that will further help identify the difference.

How can you tell the difference?

- Spinel has zero birefringence. Taaffeite is doubly refractive. A polariscope is an inexpensive and very satisfactory instrument for the detection of double refraction. This would be first stage separation in the field since if you find a gem that looks like a spinel and is doubly refractive, then you know it is not spinel and could POSSIBLY be taaffeite.

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