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Department of Geology, Faculty of Science, Ain Shams University, Abbasia, Cairo, Teachers Institute of Education, El-Odylia, Kuwait, Earth Sciences Laboratory, National Research Centre, Dokki, Cairo and Teachers Institute of Education, El-Shamia, Kuwait.

ABSTRACT

The purpose of this paper is to study the textural variations of Ras Barud granitic rocks. It is evident that the microcline perthite of the buff granites is characterised by the presence of poikilitic albite which is formed through the action of Na-bearing solutions penetrating the fissures of the unmixed perthite. The occurrence of exsolution and replacement processes at high and low temperatures respectively is responsible for the formation of the examined microcline perthite in the buff granites. The microcline perthite of some examined adamellites contains albite, quartz, and muscovite in its cracks indicating deposition from external solutions. The shape and nature of the graphic intergrowths between orthoclase and quartz in the red and pink granites are controlled by kinetic factors during the simultaneous crystallization of magma under vapour-rich and rapid cooling conditions. The intergrowth relation between perthite, microcline perthite and quartz in the greyish-white and buff granites suggests that sodic and silicic solutions have attacked the K-feldspar and given rise to perthite and microcline perthite which are cut by quartz rods forming graphic texture. The granophyres of the white granite are mostly formed by a very rapid simultaneous growth between quartz and feldspars.