Kogarkoite: Gemstone Information

Kogarkoite is Na3(SO4)F and forms transparent to translucent pale sky blue to colourless pseudorhombohedral crystals of the monoclinic system with frequent twinning; the hardness is 3.5 and SG 2.68. The mineral is water soluble. The RI for the alpha, beta and gamma rays is 1.439, 1.439 and 1.442: as kogarkoite though biaxial positive is nearly uniaxial positive,the RI for the ordinary and extraordinary rays is given, at 1.435 and 1.439 with birefringence 0.003. Under LWUV there may be a white fluorescence and under SW a pale blue fluorescence. Kogarkoite occurs in sodalite syenite xenoliths associated with an intrusive alkalic gabbro-syenite complex at Mt Saint Hilaire, Quebec, Canada.