Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
ConchoidalGemdat.org, Management Team (2012), ConchoidalGemdat.org, Management Team (2012)
Tourmaline is a series of several different minerals with unique chemical formulas. See The chemical formula of Tourmaline for details.
(Fe,Mg) 3Al 2(SiO 4) 3gemdat.org , Management Team (2012)