Handbook of mineralogy (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Uneven
Na x[Fe2+2(Al,Fe3+ )]Al 6(BO 3) 3Si 6O 18(OH) 4Anthony et al , Handbook of mineralogy (2001)
Mg 3Al 6(Si,Al,B) 5O 21(OH)Walter Schumann , Gemstones of the world (2001) More from other references