The main difficulty in the quantitative mineral analysis of rocks is connected with the variable nature of the mineral species. In the present paper a combined method (and a corresponding computer program) is proposed, which practically overcomes this difficulty. This method is based on linear equations, which are a combination of the chemical mass-balance equations with those of the quantitative X-ray diffractometry, and can perform (completely or partly) both the quantification and the chemical characterization of the minerals on several rock samples simultaneously, demanding only easily accessible initial information, such as: (i) major element (oxide) compositions for the samples; (ii) qualitative mineral composition of the samples; (iii) X-ray intensities for one or few nonoverlapped reflections of the crystalline minerals (not necessarily of all): (iv) some characteristic data for the phases (i.e., chemical composition data), if these are accurately known. Where it is possible the minerals may be expressed via end members. The samples may contain amorphous phases and/or phases without X-ray data. From the general case some very simple partial cases are derived, demanding less initial information. This method has the following advantages over the previous ones of similar philosophy: (i) drastic reduction of the number of required samples; (ii) sufficiency of equations for any analytical problem; (iii) possibility of performing partial analysis when a complete one is impossible; (iv) possibility of using the same end member in more than one solid solution. Analysis examples are given.