Uneven, UnevenArthur Thomas, Gemstones (2009), Brittle
Conchoidal, Conchoidal, Gemstones of the world (2001)
MnPO 4Walter Schumann , Gemstones of the world (2001) More from other references
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references