Conchoidal, Conchoidal, Gemstones of the world (2001)
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references
Na 3(Na,K)Al 4Si 4O 16Ulrich Henn and Claudio C.