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