Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Conchoidal, Brittle
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.
Fe 2O 3Arthur Thomas , Gemstones (2009)