Uneven, Uneven, Gemstones of the world (2001) More from other references
Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
Ca 10Mg 2Al 4(SiO 4) 5(Si 2O 7) 2(OH) 4Ulrich Henn and Claudio C.
Na 2(Ti,Fe)Si 4(O,F) 11Ulrich Henn and Claudio C.