In this work, the fine grains of Phosphate rocks forming minerals (francolite-Ca5(PO4,CO3)3F,OH) which belong to the geological formation of phosphate rocks of Zagros mountains in IRAN were detected, analyzed and interpreted by SEM-EDX in nano-scale. Moreover, the results are compared with the results of XRD analysis and straight observations of samples through the polarized microscope. Finding the composition of elements in minerals is the best path finder and also is very important in many geological investigations. The fine grain Phosphate minerals perform as traps which attract some kinds of elements. But sometimes these minerals are very fine and it is too difficult to determine and separate them for further studies. For instance, interpretation and investigation of the composition of fine minerals in Nano-scale by using single crystal X-ray Diffraction (Single-crystal XRD) analysis is impossible. Due to variety of minerals phases in a rock sample, the interpretations of the results of total elemental analysis, for example XRF, ICP, are not so real. Therefore, the best method for determination of elements in fine grain rock forming minerals is the study of minerals by the Scanning Electron Microscopy (SEM), with Energy Dispersive X-Ray Analysis (EDX).
