ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Al 2Be 3Si 6O 18Martin H.
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)