Conchoidal, Conchoidal, Gemstones of the world (2001)
Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references
(Mg,Fe) 5(SiO 4) 2(F,OH) 2Ulrich Henn and Claudio C.