Element distributions in specific igneous rocks—VIII

Abstract

158 sets of observations on element distributions in igneous rocks have been summarized and examined. The great majority of distributions show positive skewness, sometimes quite extreme, and are referred to as lognormal-type distributions. Only two elements, Si and K, show distinct tendencies for negative skewness in some igneous rocks. For the most part, these tendencies in frequency distributions are considered to be characteristic and not due either to sampling procedures or analytical error (positive skewness only) as recently suggested by Butler. Because of the prevalence of skewness, average concentrations of elements in igneous rocks seldom equal the most frequent (typical) concentrations. Usually the average is greater than the typical concentration, because of the common tendency for positive skewness.