ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
SiO 2Walter Schumann , Gemstones of the world (2001)
Na 2(Ti,Fe)Si 4(O,F) 11Ulrich Henn and Claudio C.