A stone piece from a granite patina of Peruvudaiyaar (Brihadisvara) Temple, Thanjavur is taken and examined its chemical weathering features on its outer surfaces directly under EDAX attached Scanning Electron Microscope. Three grains of feldspars are identified in the piece of granite stone and 29 points were selected on outer surfaces of these 3 grains of feldspar. The analyses were calculated on the basis of 32 (O) ions to study the intensity of insitu weathering of the grains of feldspar. The EDAX analyses show that grain I and II were subjected to extensive leaching of removal weathered products of alumina (kaolinite) and carbonates (bicarbonates and carbonates) with residual enrichment of silica. This feature is due to direct exposure of the feldspar grain surfaces to differential weathering by direct alternate attack of sunlight and rainfall over a period of one thousand years. On the other hand grain III was subjected to extensive chemical weathering leading to precipitation of kaolinite and carbonate at the expense of silica by slow infiltration of rainwater during this period. The grain III associated with cavity is located at the shadow region of rainfall attack in the granite patina stone piece. Coatings of corrosive resistant paintings may preserve and protect the structure to a certain extent