Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Mg 2Al 4Si 5O 18Ulrich Henn and Claudio C.
(Ca,Fe,Mn,Mg) 3Al 2BSi 4O 15(OH)Walter Schumann , Gemstones of the world (2001) More from other references