ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Brittle, Metallic, Brittle, Metallic, Brittle, Metallic
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
(Na,Fe,Ca)Si 2O 6Ulrich Henn and Claudio C.