ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Irregular/uneven, UnevenArthur Thomas, Gemstones (2009)
Al 2Be 3Si 6O 18Martin H.
CaAl 2Si 4O 12 -6H 2OArthur Thomas , Gemstones (2009)