Uneven, Conchoidal, Brittle, Metallic, ConchoidalArthur Thomas, Gemstones (2009)
Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
Ca 3Cr 2(SiO 4) 3Ulrich Henn and Claudio C.
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references