Gems, Sixth Edition (2006), Gems, Sixth Edition (2006)
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
SiO 2Michael OâDonoghue , Gems, Sixth Edition (2006)
Al 2Be 3Si 6O 18Martin H.