Sugilite: Gemstones Information

Sugilite is KNa2(Fe3,Mn3,Al)2Li3Si12O30 and most commonly occurs as interlocking aggregates of subhedral grains forming compact masses in the hexagonal system with a light brownish yellow to a bright magenta colour, hardness 5.5–6.5, SG near 2.74. The RI for the ordinary and extraordinary rays is 1.595–1.611, 1.590–1.607, uniaxial negative, birefringence 0.003–0.005. The absorption spectrum shows a weak diffused band centred at 570 nm, with a strong band at 419 and a weak band at 411 nm. Sugilite occurs in an aegirine-bearing syenite stock in biotite granite in bedded manganese deposits; ornamental translucent facetable sugilite comes from the Wessels and N’Chwaning mines, Kuruman, Cape Province, South Africa. A further source has been found in Tadjikistan and at Mt Saint-Hilaire, Quebec,Canada.