Major Element Geochemistry

Abstract

This chapter deals with the use of major elements in geochemistry. We first cover the important topic of the classification of fresh or relatively less-altered volcanic rocks, for which the mass-balance based CIPW norm (Cross et al. in Journal of Geology, 10, 555–690, 1902) procedure of Verma et al. (in Schweizerische Mineralogische und Petrographische Mitteilungen, 83, 197–216, 2003) is presented and related computer programs are pointed out. The chemical classification of plutonic rocks is covered, but the difficulties with the use of ternary diagrams for the mineralogical classification are dealt with first. Similarly, the difficulties with the other highly used classification diagrams are pointed out. Then, after commenting on the classification of sedimentary rocks, the shortcomings of the frequently-used weathering indices are discussed. The chapter ends with the adverse evaluation of the existing major element concentration-based diagrams for both igneous and sedimentary rocks, which has made is clear that geochemometric solutions to the problem of the nomenclature and tectonic discrimination should be proposed.