Conchoidal, Conchoidal, Gemstones of the world (2001)
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001)
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)