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