ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Uneven
SiO 2Walter Schumann , Gemstones of the world (2001)
(Al,Mg) 8(Al,Si) 6O 20Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references