CIPWnorm

CIPWnorm is a method used in geochemistry to standardize the chemical composition of igneous rocks into a normative mineralogy. The "CIPW" stands for Cross, Iddings, Pirsson, and Washington, the geologists who developed the system in the early 20th century. The goal of CIPWnorm is to convert the weight percentages of oxides in a rock's chemical analysis into hypothetical mineral abundances. This is done by assuming certain crystallization temperatures and a sequence of mineral precipitation based on thermodynamic principles.

The process involves a series of calculations that prioritize certain elements and oxides to form specific minerals. For example, silica (SiO2) is allocated to quartz or feldspars, while calcium (CaO) is preferentially assigned to plagioclase feldspar. Other oxides like MgO and FeO are used to form mafic minerals such as olivine and pyroxene. Trace elements and volatile components are generally ignored in the standard CIPWnorm calculation.

The output of a CIPWnorm calculation is a list of normative minerals and their weight percentages, such as normative quartz, feldspar, olivine, and pyroxene. This normative mineralogy can be useful for classifying igneous rocks, comparing different rock compositions, and inferring petrogenetic processes. It provides a standardized way to represent the mineralogical potential of a rock based solely on its bulk chemical composition, regardless of whether those minerals are actually present in the rock or in what proportions. CIPWnorm is a widely used tool in igneous petrology, although its assumptions and limitations are also recognized.