Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Handbook of mineralogy (2001)
(Ca,Fe,Mn,Mg) 3Al 2BSi 4O 15(OH)Walter Schumann , Gemstones of the world (2001) More from other references
Na x[Fe2+2(Al,Fe3+ )]Al 6(BO 3) 3Si 6O 18(OH) 4Anthony et al , Handbook of mineralogy (2001)