ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, UnevenArthur Thomas, Gemstones (2009)
SiO 2Walter Schumann , Gemstones of the world (2001)
KCa 4Si 8O 20(F,OH) · 8H 2OUlrich Henn and Claudio C.