Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Na 2(Ti,Fe)Si 4(O,F) 11Ulrich Henn and Claudio C.
Al 2Be 3Si 6O 18Martin H.