NORRRM-package: Geochemical Toolkit for R
In NORRRM: Geochemical Toolkit for R

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According to the IUGS (International Union of Geological Science), Subcommission on the Systematics of Igneous Rocks, the primary classification of igneous rocks must be based according to their modal mineral composition, expressed in volume percent. Nevertheless, where these data are not available or can not be determined owing to fine-grained mineral assemblage, glassy content or changes in the original mineralogy, then other criteria based on chemical bulk composition may be used.

Computed from the chemical composition, the normative mineralogy is an alternative approach for mineralogical classification and useful for set up the naming of igneous rocks (as parts of the TAS classification, TASplot). The CIPW Norm is the most commonly used calculation algorithm to estimate the standard mineral assemblages for igneous rocks CIPW, generated over more than a hundred years ago and thereafter modified by some authors to the passage of the years (e.g., Verma et al., 2002). It is based upon assumptions about the order of mineral formation and known phase relationships of rocks and minerals, using simplified mineral formulas.

In the option CIPW.trace, the trace elements that can be used are Ba, Cl, Co, Cr Cs, F, Li, Ni, Rb, S, Sr, V and Zr. Additionally, the oxides concentrations of Cr2O3, NiO and SO3 (expressed as wt. percent) are handled like trace elements as well. However Cr2O3 are preferable to Cr and NiO to Ni. Sulfur concentration when available is reported as either SO3 or S, in which case their separate identity should be maintained.