Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
Splintery, Granular, Splintery, Granular, Gemstones (2009)
Na 2(Ti,Fe)Si 4(O,F) 11Ulrich Henn and Claudio C.
Ca 2(Mg,Fe) 5(OH) 2Walter Schumann , Gemstones of the world (2001) More from other references