ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
SiO 2Ulrich Henn and Claudio C.
(Ca,Cr)MgSi 2O 6Gemdat.org , Management Team (2012)