ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Al 2Be 3Si 6O 18Martin H.
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references