A RAPID METHOD FOR QUANTITATIVE MICROPROBE ANALYSIS OF OLIVINES, PYROXENES AND FELDSPARS

Abstract

A rapid method for the quantitative microprobe analysis of some rock-forming minerals with solid solution relationships is proposed and the determinative diagrams of the compositions of olivines, pyroxenes and feldspars are given. Determinative curves of X-ray relative intensities to the molar ratio of the end members are calculated on the basis of their ideal chemical compositions under the following conditions; X-ray take-off angle 40° and accelerating voltage 15 KV. The errors of molar ratio due to the deviation from the ideal composition, vertical or lateral displacement of specimen surface, drift of beam current intensity, and difference of carbon film thickness are evaluated in detail, and it is found that the errors are mostly within±l.0 mol%. It is concluded that the proposed method is rapid and accurate, and enables us to analyse a number of specimens for a short time. The utility of the proposed technique to some petrological problems is also discussed.