ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Conchoidal, Brittle
SiO 2Walter Schumann , Gemstones of the world (2001)
Mn 3Al 2(SiO 4) 3Arthur Thomas , Gemstones (2009)