Conchoidal, Conchoidal, Gemstones of the world (2001)
Irregular/uneven, UnevenArthur Thomas, Gemstones (2009)
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references
CaAl 2Si 4O 12 -6H 2OArthur Thomas , Gemstones (2009)