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