USA, Southern and central Africa, green, blue, China, India, USA, Italy, green, blue, China, India, USA, Italy
Southern and central Africa
H 4Mg 3Si 2O 9Walter Schumann , Gemstones of the world (2001) More from other references
Na 4(Al,Si) 12O 24Cl to Ca 4(Si,Al) 12O 24(CO 3,SO 4)Arthur Thomas , Gemstones (2009)