Uneven, UnevenArthur Thomas, Gemstones (2009), Brittle
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
MnPO 4Walter Schumann , Gemstones of the world (2001) More from other references
SiO 2 + H 2OUlrich Henn and Claudio C.