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 · nH 2OWalter Schumann , Gemstones of the world (2001)