X-Ray-Emission Microanalysis of Rock-Forming Minerals II. Olivines

Thirty-six olivines have been analyzed by X-ray emission techniques for Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, and Zn to extend and improve previous analyses of the same samples by Smith and Stenstrom (1965). There is excellent agreement with bulk chemical analyses for certain suites of samples but poor agreement for other samples. At least some of the poor agreement is caused by impurities. Thirty-two out of thirty-six microprobe analyses yield oxide totals between 99 and 101 per cent, and twenty-nine out of thirty-six give sums of formula units, calculated from the octahedral cations, within 99 and 101 per cent. Atomic proportions in tetrahedral and octahedral sites differ by not more than 3 per cent from stoichiometry. Titanium, Mn, and Zn are higher in Fe-rich samples, Cr and Ni in Mg-rich samples, though environmental factors also are important. Calcium increases markedly with presumed temperature of crystallization and is negatively correlated with Mg.