Myrmekite in graphic granite and in vein perthite

Abstract
This paper describes the occurrence of myrmekite in a graphic quartz-microcline-rock from the mica-bearing pegmatites of Kodarma, Bihar, India. The myrmekite has grown out from the quartz-mierocline junctions into the potash-felspar with the appearance of having replaced the latter. The two are in optical and crystallographic continuity and, owing to the large ‘single crystal’ character of the microcline, definitely oriented sections can readily be prepared. A detailed study of these sections shows that the myrmekite has been formed by the segregation and coalescence of microperthitic albite formerly held in solid solution in the potash-felspar. Successive stages in this process of segregation can be observed.These sections also provide evidence of the paragenetic relationship between the quartz rods, the vein perthite, and the body microcline. This is supplemented by additional evidence from graphic granites and vein perthites obtained from other localities.

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