Clay formation in saprolites of igneous rocks under semiarid to arid conditions, negev, southern israel
1984
SINGER, ARIEH
This paper reports the results of a study of the mineralogical composition of the clay (< 2 μm) fractions separated from four saprolites of igneous rocks in the Negev desert, southern Israel. Clay contents in the saprolites, calculated by comparing specific surface areas of these clays with those of the saprolites were 45, 53, 11.3, and 37% in the saprolites derived from andesitic basalt, Na-basanite, microgranite, and microdiorite, respectively. The Na-basanite had altered into a dioctahedral smectite, and the andesitic basalt into a hydroxy-interlayered, high-charge smectite. Smectite and chlorite are the major alteration products of the microgranite and are accompanied by moderate amounts of kaolinite. Mica and osmectite had formed as the result of the desert weathering of microdiorite. Crystalline iron oxides appear only in the clay fraction from the basic rocks—saprolite. Mica formation appears to be conditioned by the previous sericitization of feldspar minerals. Argillation appears to affect preferentially the mafic constituents of the rock and not to involve significant leaching losses.
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