Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Ca 3Al 2(SiO 4) 3Arthur Thomas , Gemstones (2009)
(Fe,Mn)Ta 2O 6Walter Schumann , Gemstones of the world (2001) More from other references