Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Mg 2Al 4Si 5O 18Ulrich Henn and Claudio C.
CaZrBAl 9O 18Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references