ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Uneven
SiO 2Ulrich Henn and Claudio C.
FeS 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references