Uneven, Subconchoidal, Uneven, Subconchoidal, Conchoidal, Brittle
ConchoidalArthur Thomas, Gemstones (2009)
NaAlSi 2O 6 · H 2OMichael OâDonoghue , Gems, Sixth edition (2006) More from other references
Tourmaline is a series of several different minerals with unique chemical formulas.