ConchoidalArthur Thomas, Gemstones (2009)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Tourmaline is a series of several different minerals with unique chemical formulas.
BaTiSi 3O 9Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references