Uneven, Conchoidal, Brittle
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
(Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2
MgAlBO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references