ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Irregular/uneven, UnevenArthur Thomas, Gemstones (2009)
SiO 2Walter Schumann , Gemstones of the world (2001)
CaAl 2Si 4O 12 -6H 2OArthur Thomas , Gemstones (2009)