UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references