Zoned Plagioclase from the Charnockites of Kondapalli, Krishna District, Andhra Pradesh, India

C. Leelanandam
Department of Mineralogy and Petrology, Downing Place, Cambridge1
1Present address: Geology Department, Osmania University, Hyderabad 7, India.

Summary: Zoning in plagioclase is reported from the charnockitic rocks of Kondapalli, Krishna district, Andhra Pradesh, India, for the first time. Electronprobe studies indicate that the zoned plagioclases consist of homogeneous sodic cores mantled by thin calcic shells, which show continuous zoning of the inverse type. Partial chemical analyses of twelve density fractions of the zoned plagioclase from a basic charnoekite exhibit a wide variation in An content from 54·80 to 72·39 %; X-ray studies suggest that they possess ‘fixed’ transitional structural state.

Mineralogical Magazine; June 1968 v. 36; no. 282; p. 805-813; DOI: 10.1180/minmag.1968.036.282.07
© 1968, The Mineralogical Society
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