Taaffeite

Taaffeite is very rare, and is unique in being the only gemstone not recognized as a new mineral species until it had been faceted. The first specimen was found by Count Taaffe in Ireland, in a jeweller’s box of stones.

It looked like spinel, had a pale mauve tinge, and was cushion-cut, but was eventually found to be a new, doubly refractive (rather than singly refractive like spinel) mineral. Since then, more specimens have been found; these range in hue from red to blue to almost colourless.

Taaffeite occurs in Sri Lanka, China, and the former USSR. No imitation taaffeites appear to exist.

Taaffeite Properties

Chemical Composition: 
Oxide of beryllium, magnesium aluminium - BeMg3Al8O16 + Fe, Mn, Zn, Cr
Colors / Varieties: 
Purple, violet, red, blue, brownish purple
Crystal System / Forms: 
Hexagonal System / Pyramidal, bi-pyramidal and often truncated by basal pedion (hemimorphic)
Hardness: 
8
Specific Gravity: 
3.62 ± 0.03
Cleavage / Fracture: 
None / Conchoidal fracture
Optic Character: 
Anisotropic, D.R.; Uniaxial negative
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.718 - 1.722 / 0.004
Pleochroism: 
Weak
Dispersion: 
0.019
Magnification: 
Crystals (spinel etc.), two phase inclusions, liquid fingerprints
U.V. Fluorescence: 
Inert
Spectrum: 
Not characteristic
Cause of Color: 
Pink / Red: Chromium
Simulants (with separation tests): 
Natural spinel (optic character), Idocrase (spectrum, S.G.), Sapphirine (R.I., S.G.), etc.
Geological Occurrence: 
In metamorphosed limestone as rolled pebbles.
Sources: 
Sri Lanka, Russia (Eastern Siberia), China
Cuts & Uses: 
Facetted cuts.