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