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