Colorless, White, Brownish, Reddish, Black, Brownish, Black, Colorless, gray, White, Reddish, Brown
White, Colorless, Blue, Red, Green, Yellow, Violet
Na 3AlF 6Ulrich Henn and Claudio C.
SiO 2Walter Schumann , Gemstones of the world (2001)
Gemmological Tables (2004) More from other references
TranslucentWalter Schumann, Gemstones of the world (2001)