FIRST DIAMOND-BEARING PHLOGOPITE PYROXENITE FIND (A XENOLITH FROM THE MIR KIMBERLITE PIPE, YAKUTIA)

Abstract

To settle the question of whether phlogopite can exist at high pressures and temperatures in upper mantle rocks, the authors give the results of their study of a diamond-bearing phlogopite pyroxenite specimen from the Mir kimberlite pipe, constituting a mineral association a priori known to be of the high-pressure kind. The fragment of a compositionally unique xenolith high in phlogopite (12 percent), with large isolated crystals of diamond. The main minerals of this very striking, variegated, green and orange xenolith are garnet, clinopyroxene and phlogopite. They are present as large grains, among which, on the inner shear surface of the specimen, there is a large diamond crystal. The secondary minerals in the true sense, i.e., formed by protomagnetic partial melting, include hornblende, plagioclase, hercynite and second-generation phlogopite. The rock is coarse grained and idiomorphic.