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)
SiO 2Walter Schumann , Gemstones of the world (2001)
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)