Magnetic Chromites from Kondapalli, Andhra Pradesh, India

A. T. Rao
Department of Geology, Andhra University, Waltair-530003, India

Synopses: The Kondapalli region (16° 37′ N. 80° 32′ E.) in the Eastern Ghats, Andhra Pradesh, consists of high-grade granulite facies rocks: charnockites, hypersthene granites, and enderbites are plutonic intrusives into khondalites—garnetiferous sillimanite granites, garnetiferous granites, siltimanite-garnet quartzites, and quartzites. Pyroxene granulites of gabbroic and noritic compositions are distinct basic intrusive bodies, occurring as sills and dykes.

Chromite orthopyroxene nodules are enclosed in serpentinite and carbonate rock, formed from altered peridotite; they are younger than the charnockites and pyroxene granulites and are confined to the cores of south-eastern-plunging overturned isoclinal anticlines. The chromites are massive in coarse-layered pyroxenites and granular in fine-layered rocks; those found at Gangineni are magnetic and are associated with bronzite (En77–85), those from the Binny and Loya mines are non-magnetic and associated with enstatite (En88–95).

Chemical analyses and X-ray powder data are given for five specimens, including both types. The magnetic susceptibility appears to increase with increasing Fe3+. The unit-cell size is negatively correlated with Cr3+, A13+, and Mg2+ and positively with Fe2+ and Fe3+.

Mineralogical Magazine; September 1978 v. 42; no. 323; p. 406; DOI: 10.1180/minmag.1978.042.323.14
© 1978, The Mineralogical Society
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