Mineralogical composition of some feldspars used as raw material in ceramics was studied by X-ray powder diffraction. Quantitative analysis of mineral phases present in these ceramic raw materials were performed using full-pattern Rietveld and standardless quantification methods. Mineral phases identified and quantified results using the above two methods are compared with the CIPW norm that uses theoretical mineral composition based in chemical analysis. In order to obtain an indication useful and realistic from mineral phases abundance will be discussed the characteristics of the mineral phases identified by X-ray diffractometry, chemical analysis results and calculated normative composition.