Conchoidal, Conchoidal, Gemstones of the world (2001)
Irregular/uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001)
Na 2Ca 2Al 6Si 6O 24(CO 3) 2Walter Schumann , Gemstones of the world (2001) More from other references