ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Al 2Be 3Si 6O 18Martin H.
(Ca,Cr)MgSi 2O 6Gemdat.org , Management Team (2012)