ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
Al 2Be 3Si 6O 18Martin H.
BaSO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references