Conchoidal, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
Brittle, UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
PbCu(SO 4)(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)
(Mg,Fe)Al 3(BO 4)(SiO 4)OUlrich Henn and Claudio C.