Smectites are dominant clay minerals in bentonites. Each of montmorillonite, beidelite, nontronite, hectorite and saponite minerals is a member of smectite group. They are valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive capacity and catalytic activity. Chemical analysis in combination with other techniques is suitable for the quantitative determination of smectite minerals in natural bentonites. Chemical formula of a smectite which is important to choose its industrial uses can be calculated from Chemical analysis. The converting a Chemical analysis of a smectite mineral into a Chemical formula was discussed in this study depending on various parameters.