ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Uneven
Uneven, Conchoidal, Brittle
(Al,Mg) 8(Al,Si) 6O 20Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
(Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2