Vivianite (Fe3(PO4)2•E8H2O), an iron phosphate mineral has been identified in biomats produced around As polluted tubewell, which is used for drinking water in Hazigonj, Chandpur, Bangladesh. The As polluted groundwater and biomats (brown, green and gray) were analyzed by ED-XRF, XRD and optical microscopy, complimented with SEM-EDX. The biomats are composed mainly of metabolically active microorganisms such as coccus, bacillus and filamentous types of bacteria and algal filaments. A small

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... t of As accumulation in biomats is evidenced by SEM-EDX. Furthermore, X-ray powder diffraction patterns revealed that the formation of vivianite in different colored biomats (brown, green, brown and gray), which is a secondary mineral composed mainly of P and Fe, in association with quartz, feldspars, illite, chlorite and cordierite. Vivianite possibly contains a small amount of As by isomorphic substitution for P, resulting solid solution of symplesite. The microorganisms may play an important role in mineralization of iron phosphates.