Basaltic lava flows of Maku area is the largest quaternary basalt of the north west of Iran, which is erupted from newest activity stage of Ararat Mountain volcanoes. Important portion of these lavas are reached the river Sari so and Bazargan Plain from eastern and southern slopes of the Ararat that after covering of this plain it has changed the route to wards the Maku valley of the Zangmar river and from their inters in to the Poldasht Plain. This non-carbonate fractured rocks is covered the old rivers alluvial and formed a good basaltic- alluvial aquifer in the area. Amount of fluoride ion in the water of this aquifer is more than the universal maximum admissible concentrations. All the people of villages that their drinking water supplies from basaltic springs and wells are suffering from dental and probably skeletal fluorosis. In this study for determining the source of high fluoride concentrations in the groundwater of the basaltic area in addition to studying 11 microscopic tine sections from basaltic rocks of the study area, three series water sampling from the springs and rivers were carried on and chemically were analyzed. The water analysis results and basaltic rocks petrography indicate the high fluoride water inters the study area from the river Sari so route
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