Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Uneven
Na 2(Ti,Fe)Si 4(O,F) 11Ulrich Henn and Claudio C.
Mg 3Al 6(Si,Al,B) 5O 21(OH)Walter Schumann , Gemstones of the world (2001) More from other references