Sapphirine: Gemstone Information
Sapphirine is (Al,Mg)8(Al,Si)6O20 (several polytypes are recognized) and forms indistinct tabular transparent to translucent light to dark blue crystals of the monoclinic or triclinic system. The hardness is 7.5 and the SG 3.4–3.5. The RI for the alpha, beta and gamma rays is 1.701–1.726,1.703–1.728, 1.705–1.734, biaxial positive or negative, birefringence 0.006.Pleochroism is strong with a variety of shades of blue, also pale reddish or yellowish green. Sapphirine occurs in high-temperature rocks or xenoliths with abundant aluminium and magnesium and low silicon. Sakena,Vorokafotra, Bekily, Anjamiary and Betroka, Madagascar have provided crystals. GIA have reported a purplish pink Sri Lankan faceted stone of 1.54 ct with mica inclusions. An orange-red variety has been reported from Tanzania.