Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Conchoidal, Brittle
Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Fe 2O 3Arthur Thomas , Gemstones (2009)
(Be,Cs) 3Al 2Si 6O 18 · 0.5H 2OUlrich Henn and Claudio C.