Irregular/uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Conchoidal, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
Na 2Ca 2Al 6Si 6O 24(CO 3) 2Walter Schumann , Gemstones of the world (2001) More from other references
SiCArthur Thomas , Gemstones (2009)