Average Composition of Granites, the Genesis of Tektites, and Petrogenesis

Abstract

THE recent article by Lovering¹, in which the average chemical composition of tektites was compared and contrasted with the average composition of terrestrial shales, calcalkaline granites and granophyres, involves an important question which is too frequently ignored. Comparison was made with the average bulk chemical composition of shales (78 analyses from Clark's Tables), granites (72 analyses quoted by Nockolds) and acid granophyric differentiates of basic magma (35 analyses available in the literature). As a basis of discussion, it may be assumed that the bulk chemical analyses are accurate representations of each of the 185 samples involved. Probably it is reasonable to assume that each of the 185 specimens was chosen by a competent geologist as a ‘typical sample’ to represent the rock-mass concerned.