Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), (e.g. graphite).
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
PbCrO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references