Colorless, Greenish, Colorless, Green, gray, Yellow
White, Colorless, Blue, Red, Green, Yellow, Violet
Irregular/uneven, Uneven
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Ca 2Al 3(SiO 4) 3(OH)Walter Schumann , Gemstones of the world (2001) More from other references
SiO 2 + H 2OUlrich Henn and Claudio C.