Spheroidal weathering of basalt from Gebel Qatrani, Fayum Depression, Egypt

Abstract Background Three stages of basalt weathering are known: early or incipient weathering, intermediate and advanced weathering. The Late Oligocene Gebel Qatrani in Fayum Depression, Egypt, shows signs particularly exhibited spheroids found at the top flow. present paper gives results detailed petrographical, mineralogical geochemical study these spheroids. Results core-stones composed phenocrystals plagioclase feldspars clinopyroxenes set a groundmass tiny pyroxenes, relatively altered olivine opaque minerals. is subalkali (tholeiitic). outer weathered shells surrounding partly pyroxenes. calculated indices show that there marked trend from to shells. chemical mobility elements depletion Mg, Ca, Na K due olivine, pyroxene feldspars. trace Rb, Sr, Ni, V, Cr Zn also depleted. Conclusions Qatrani, type. degree corresponding indicates occurred under predominantly semiarid arid conditions.