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 3Al 2(SiO 4) 3Arthur Thomas , Gemstones (2009)