Uneven, Splintery, Conchoidal, Uneven, Splintery, Conchoidal, UnevenWalter Schumann, Gemstones of the world (2001)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
SiO 2Arthur Thomas , Gemstones (2009)
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.