ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, UnevenArthur Thomas, Gemstones (2009), Brittle
Al 2Be 3Si 6O 18Martin H.
MnPO 4Walter Schumann , Gemstones of the world (2001) More from other references