Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Uneven
Mg 2Al 4Si 5O 18Ulrich Henn and Claudio C.
Mg 3Al 6(Si,Al,B) 5O 21(OH)Walter Schumann , Gemstones of the world (2001) More from other references