Redox estimation from a calculation of Eu 2+ and Eu 3+ concentrations in natural phases

Abstract

Assumption of the equivalence of Eu 2+ and Sr interphase partitioning permits the calculation of the Eu 2+ and Eu 3+ concentrations in each of any two equilibrated phases of known Sr and rare-earth concentrations. The calculation has been applied to a number of porphyritic terrestrial lavas, two lunar samples and two basaltic achondrites. Multiphase rocks generally give internally consistent results. The potential size of the positive Eu anomaly in feldspars appears to increase with decreasing feldspar anorthite content. The potential size of the negative Eu anomaly in clinopyroxenes appears to increase with increasing pyroxene iron content. A mica apparently has a positive Eu anomaly. The typical basalt Eu 2+/Eu 3+ ratio is about 0.15. No correlation of Eu 2+/Eu 3+ and FeO/Fe 2O 3 was found for the terrestrial samples. Calculated and estimated differences in terrestrial and lunar oxygen fugacities appear to be in agreement.