Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
(Ca,Mn2+ ,Fe2+ ) 3Al 2BSi 4O 15(OH)Anthony et al , Handbook of mineralogy (2001)
(Na,Ca,K) 8(Si,Al) 12O 24(SO 4,Cl,CO 3) 3(H 2O)Arthur Thomas , Gemstones (2009)