ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Brittle, Metallic, Brittle, Metallic
SiO 2Ulrich Henn and Claudio C.
Na 2ZrSi 3O 9 · 2H 2OMichael OâDonoghue , Gems, Sixth Edition (2006)