Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), (e.g. graphite).
SiO 2Ulrich Henn and Claudio C.
PbCrO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references