Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Mg 2Al 4Si 5O 18Ulrich Henn and Claudio C.
KAlSi 2O 6Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references