Abstract: Major, minor, and trace elements were measured with electron and ion microprobes for eighteen anorthoclase megacrysts from five locations. Comparisons with concentration ranges tabulated by Smith (1974) show excellent agreement except for consistently lower values of Mg and B. The discrepancy for Mg probably reflects Mg-rich impurities contaminating samples analysed by bulk methods. The cause of the discrepancy for B is unknown and deserves further study. Samples from Mt. Erebus, Antarctica, contain glass inclusions from which the following crystal/liquid partition coefficients ensue: Mg, 0.008; P, 0.04; Ti, 0.08; Fe, 0.04; Ba, 5.2; Sr, 8; Rb, 0.27.