Irregular/uneven, Uneven
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Ca 2Al 3(SiO 4) 3(OH)Walter Schumann , Gemstones of the world (2001) More from other references
(Ca,Mn2+ )Si 3O 9Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references