Normative mineralogy is a calculation of the composition of a rock sample that estimates the idealised mineralogy of a rock based on a quantitative chemical analysis according to the principles of geochemistry.
Normative mineral calculations can be achieved via either the CIPW Norm or the Barth-Niggli Norm (also known as the Cation Norm).
Normative calculations are used to produce an idealised mineralogy of a crystallized melt. First, a rock is chemically analysed to determine the elemental constituents. Results of the chemical analysis traditionally are expressed as oxides (e.g., weight percent Mg is expressed as weight percent MgO). The normative mineralogy of the rock then is calculated, based upon assumptions about the order of mineral formation and known phase relationships of rocks and minerals, and using simplified mineral formulas. The calculated mineralogy can be used to assess concepts such as silica saturation of melts.
Because the normative calculation is essentially a computation, it can be achieved via computer programs.