Conchoidal, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
PbCu(SO 4)(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)
SiO 2Ulrich Henn and Claudio C.