PX-NOM—an interactive spreadsheet program for the computation of pyroxene analyses derived from the electron microprobe

Abstract

PX-NOM is a Microsoft Excel™ spreadsheet program that enables the user to calculate structural formulae of pyroxene analyses obtained from the electron microprobe and to determine respective pyroxene names according to the classification scheme of the International Mineralogical Association. The nomenclature used in the program contains only mineral names and adjectival modifiers accepted by the Subcommission on Pyroxenes. Additionally, PX-NOM permits the use of the jadeite+quartz geobarometer for clinopyroxenes containing jadeite as well as various garnet-clinopyroxene Fe–Mg exchange thermometers. The barometer calculates a minimum pressure, if only secondary plagioclase is available in the mineral assemblage and therefore X Ab Pl has to be set to 1. The exchange thermometers show best results in LT-MT eclogites which bear only low contents of high-Si phases (quartz, feldspar). Pyroxene analyses belonging to the Ca–Fe–Mg, Ca–Na or Na group can be plotted in the Wo–Fs–En triangle or the Quad-Ae-Jd diagram, respectively. The diagrams are presented on separate sheets and can be manipulated and printed optionally.