ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Metallic
Be 3Al 2Si 6O 18Ulrich Henn and Claudio C.
CuSMichael OâDonoghue , Gems, Sixth edition (2006) More from other references