Distinguishing Taaffeite from Musgravite: Raman spectroscopy and birefringence tests?
4 Answers from travellers
Taaffeite and Musgravite (Magnesiotaaffeite-6N'3S) are among the rarest collector gemstones in the world, frequently misidentified as mauve or violet spinel. Spinel is singly refractive (isotropic) and inert under a polariscope. Taaffeite is doubly refractive (uniaxial negative) with refractive indices of 1.717 to 1.724 and a birefringence of 0.004-0.005. Distinguishing Taaffeite from Musgravite cannot be achieved with field refractometers; it demands Raman spectroscopy or high-resolution X-ray powder diffraction (XRD) at the NGJA laboratory to count magnesium-beryllium polytype layers.
A portable polariscope is essential in field markets; rotating a faceted mauve stone between crossed polarizers identifies double refraction within seconds.
Authenticated multi-carat musgravite stones command high prices among international collectors; ensure you declare proper values for export insurance.
Never purchase high-value rare collector stones based purely on handwritten regional dealer certificates without independent laboratory confirmation.
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