Mn-olivine from Gangpur Group of Rocks, Orissa

Mn-olivine (tephroite) bearing assemblage is often recorded m manganese silicate-carbonate-oxide rocks metamorphosed to green schist facies condition in Precambrian Gangpur Group, Orissa Divalent Mn and Fe dominate this assemblage with most phases having high Mn/Fe ratios Minerals in the assemblage include near end member tephroite (TP_{9{} 33 90 95} Fa_{4 76 8 40} FO_{0 55 471}), rhodochrosite, pyroxmangite, Jacobsite, spessartine dominated garnet with minor quartz, apatite and barite Tephroite is sometimes altered to either Mn rich minnesotaite or to a sepiohte related mineral that resembles serpentine in Mg-olivine rocks ThIs assemblage is very likely evolved through decarbonation Oxidation processes of a carbonatic precursor under a relatively low oxygen fugacity condition.