Two Morphologies of Pyrophanite in Mn-rich Assemblages, Gangpur Group, India

B. R. Nayak and B. K. Mohapatra
Regional Research Laboratory, Bhubaneswar - 751 013, Orissa, India

Abstract: Pyrophanite is widely distributed in metamorphic Mn-rich rock assemblages of the Gangpur Group, India. It occurs in two distinct habits: as an independent phase, and as an exsolved phase within hematite. The well developed large sized crystals coexist with spessartine in Mn-silicate facies rocks. In contrast, the exsolved crystals occur as fine needle/bleb-like crystallites intergrown with hematite in Mn-silicate-oxide facies rocks. Compositionally the exsolved crystals are enriched in iron, present in both the ferric and ferrous states. The two morphologies of pyrophanite attest to their formation under different environmental conditions. The independent pyrophanite is formed from a Mn-Ti rich precursor under low oxygen fugacity conditions while the hematite-pyrophanite intergrowth evolved from an Fe-Mn-Ti rich precursor under higher fO2 conditions.

Keywords: pyrophanite • manganese deposits • hematite • Gangpur Group • India

Mineralogical Magazine; December 1998 v. 62; no. 6; p. 847-856; DOI: 10.1180/002646198548070
© 1998, The Mineralogical Society
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