USA, Southern and central Africa, green, blue, China, India, USA, Italy, green, blue, China, India, USA, Italy
Canada, Southern and central Africa
H 4Mg 3Si 2O 9Walter Schumann , Gemstones of the world (2001) More from other references
KNa 2B 3Si 12O 30Michael OâDonoghue , Gems, Sixth Edition (2006)