Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Brittle
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
(Be,Cs) 3Al 2Si 6O 18 · 0.5H 2OUlrich Henn and Claudio C.
SiO 2Walter Schumann , Gemstones of the world (2001)