A revised CIPW norm

Abstract

The CIPW norm proposed one hundred years ago is still a useful scheme because abundances of normative minerals are required for a proper rock classification such as that recommended by the IUGS. However, a standard methodology for CIPW norm computation is required. This paper presents a detailed step-by-step procedure for a Standard Igneous Norm (SIN). Our proposal is based on mass-balance principles involving the concept of variable molecular weights, free or unused parameters such as oxygen, CO2 and other oxides, and silica deficiency. This SIN is capable of providing highly consistent results, with differences between CIPW norm sums and bulk chemical analyses generally smaller than 0.002.