ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Al 2Be 3Si 6O 18Martin H.
(Mg,Fe) 5(SiO 4) 2(F,OH) 2Ulrich Henn and Claudio C.