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Twenty-two chemically analyzed clinopyroxenes near the Di-Hd join (chosen for their low content of intergrown phases) have been analyzed by microprobe X-ray-emission techniques for Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni. As far as possible, intergrown phases such as orthopyroxene and ilmenite were avoided, and some systematic bias with respect to the bulk chemical analysis is to be expected, and was indeed found, especially for Ti, Ca, and Mg. The average microprobe estimates for SiO₂ and Al₂O₃ are 0. 3 per cent greater and 0. 4 per cent less, respectively, than the mean chemical estimates, in conformity with the bias found previously for feldspars and orthopyroxenes. Systematic bias in the gravimetric techniques is suggested as the principal cause. Microprobe estimates of Mn agree well with chemical estimates but tend to be slightly higher. Most analyses for Na agree within 0. 05 per cent (all values in this abstract are given as percentages of the whole sample). Oxide totals (assuming iron is partitioned between the valence states according to the chemical determinations) range from 97. 7 to 101. 0 per cent, with seventeen out of twenty-two between 99 and 101 per cent.
J. V. Smith (Fri,) studied this question.