A chromian tourmaline from Outokumpu, Finland

Chromian tourmaline, a member of the dravite group, has been encountered in the Cr-bearing skarns occuring between the serpentinites and quartzites in the Outokumpu area, in association with chrome-bearing silicates ang oxides. The reported chromian tourmaline contains Cr2O3 9.60 %. The mineral is trigonal with a0 = 15.96 Å, c0 = 7.2d Å and D = 3.101 g/cm3. The chromian tourmaline is uniaxial, negative and very strongly pleochroic with ω = 1.687 and ε = 1.638.