Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Mg 2Al 4Si 5O 18Ulrich Henn and Claudio C.
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001)