Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001)
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Mg 2Al 4Si 5O 18Ulrich Henn and Claudio C.
(Fe,Mn)Ta 2O 6Walter Schumann , Gemstones of the world (2001) More from other references