Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001), Conchoidal, Uneven
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Mn 3B 7O 13ClMichael OâDonoghue , Gems, Sixth Edition (2006)