ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Uneven, Conchoidal, Brittle
Be 2BO 3(OH)Ulrich Henn and Claudio C.
Ca(Mg 3)MgAl 5(Si 6O 18)(BO 3) 3(OH) 3(OH)Gemdat.org , Management Team (2012)