APPLICATION OF ELECTRON PROBE SPECTRUM METHOD IN THE SPECIES IDENTIFICATION OF PYROXENE

The main identification marks of pyroxene in metamorphic rocks under microscope are high positive relief, pyroxene-type cleavage and interference color. The mineral family of pyroxene is consisted of two subfamilies:orthopyroxene and clinopyroxene. The orthopyroxene subfamily includes 7 species of pyroxene; while the clinopyroxene, 12 species. In order to verify the accuracy of rock thin section identification results, X-ray powder diffraction technique is usually used for comparative analysis. There are several kinds of pyroxene and pyroxene species in rocks, which cannot be distinguished by the X-ray powder diffraction method. This study adopts electronic probe spectrum technique to analyze the major elements of mineral and speculate the mineral name with microanalysis of chemical composition of samples. Statistics of microanalysis for 25 samples show the chemical composition of the mineral:8.36%~17.34% of MgO, 27.57%~39.77% of FeO and 47.94%~52.70% of SiO₂, with minor Cr₂O₃(0.01%~6.28%), Na₂O(0.00%~0.19%), Al₂O₃(0.43%~3.11%), CaO(0.38%~1.94%) and MnO₂(0.09%~0.79%). The chemical composition of tested samples corresponds to that of hypersthene, thus it can be determined as hypersthene.