ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
SiO 2Walter Schumann , Gemstones of the world (2001)
Mg 3(Al,Cr) 2(SiO 4) 3Gemdat.org , Management Team (2012)