ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), (e.g. graphite).
ZrO 2Arthur Thomas , Gemstones (2009)
PbCrO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references