Conchoidal, Brittle, Conchoidal, Brittle, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
ConchoidalArthur Thomas, Gemstones (2009)
PbSO 4Michael OâDonoghue , Gems, Sixth edition (2006) More from other references
Tourmaline is a series of several different minerals with unique chemical formulas.