Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Irregular/uneven, UnevenArthur Thomas, Gemstones (2009)
(Ca,Fe,Mn,Mg) 3Al 2BSi 4O 15(OH)Walter Schumann , Gemstones of the world (2001) More from other references
CaAl 2Si 4O 12 -6H 2OArthur Thomas , Gemstones (2009)