A chromian tourmaline from Outokumpu, Finland

Abstract

Chromian tourmaline, a member of the dravite group, has been encountered in the Cr-bearing skarns occurinl between the serpentinites and quartzites in the Outokumpu area, in association with chrome-bearing silicates ang oxides. The reported chromian tourmaline contains Cr2Oa 9.6 0 %. The mineral is trigonal with a" = 15.9 6 A, c" = 7.2d A and D = 3.101 g/cm 3 . The chromian tourmaline is uniaxial, negative and very strongly pleochroic with to = 1.687 and = 1.638.