“…The tourmaline supergroup minerals with general formula XY 3 Z 6 [ T 6 O 18 ][ B O 3 ] 3 V 3 W , where X = Na, Ca, K and □ (vacancy); Y = Li, Mg, Al, Cr 3+ , V 3+ , Fe 3+ , Fe 2+ , Mn 2+ , Ni and (Ti 4+ ); Z = Mg, Fe 2+ , Al, Fe 3+ , V 3+ and Cr 3+ ; T = Si, Al and (B) (Fe 3+ ); B = B and □; V = OH and O; and W = OH, F and O (Henry et al , 2011) are stable over a range of low-temperature hydrothermal to magmatic and high-pressure metamorphic conditions. They are extremely variable in composition and isomorphic substitutions, which allow their consideration as indicators of mineral-forming conditions and as an important prospecting guide (Kuzmin et al ., 1979; Slack, 1996; Henry et al ., 2008; Collins, 2010; Hinsberg et al ., 2011; Baksheev et al ., 2012).…”