Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Be 3Al 2Si 6O 18Ulrich Henn and Claudio C.