Nepheline: Gemstone Information

Nepheline is (Na,K)AlSiO4 and forms transparent to nearly opaque prismatic crystals of the hexagonal system, usually colourless but coloured variously from impurities and sometimes notably large. The hardness is 5.5–6 and the SG 2.55–2.66. The RI for the ordinary and extraordinary rays is 1.529–1.546 and 1.526–1.542, uniaxial negative with birefringence 0.004. Some German specimens may show a light blue and some from Ontario an orange fluorescence in LWUV. The variety elaeolite may be red, green, brown or grey; when minute crystals are present they may produce chatoyancy. Nepheline occurs in alkalic rocks, including nepheline syenites and pegmatites associated with them, also in gneisses.Large crystals occur particularly from Davis Hill, Bancroft, Ontario,Canada; Katzenbuckel, Saxony, Germany.