Normative analysis is defined as the calculation of a theoretical assemblage of standard minerals for a rock based, on the whole rock chemical composition as determined by analytical techniques. The original purpose for the norm was essentially taxonomic. An elaborate classification scheme based on the normative mineral percentages was proposed. The classification groups together rocks of similar bulk composition irrespective of their mineralogy. Various types of NORMs have been proposed - CIPW, Niggli, Barth. Each of theses proposals has its own specific advantages and/or disadvantages.

The CIPW norm, originally proposed in 1919, was proposed as a means of comparing and classifying all igneosu rocks for which chemical analyses wers available. The NORM takes it's name from the four authors who proposed it - Cross, Iddings, Pirsson and Washington. This NORM was very elegant and based on a number of simplifications:

1. The magma crystallizes under anhydrous conditions so that no hydrous minerals (hornblende, biotite) are formed.
2. The feromagnesium minerals are assumed to be free of Al₂O₃.
3. The Fe/Mg ratio for all feromagnesium minerals is assumed to be the same.
4. Several minerals are assumed to be incompatible, thus nepheline and/or olivine never appear with quartz in the norm.

Since the CIPW NORM was introduced in 1919 several other normative calculations have been suggested, e.g. Niggli norm, Barth mesonorm. The latter is used commonly when examining granitic rocks.

OVERHEAD - CIPW CALCULATION SHEET