Statistical Comparison between Pyroxenes from Kimberlites and Their Associated Xenoliths

Cluster analysis of 458 pyroxenes from kimberlites, associated xenoliths and diamonds has allowed recognition of 5 chemically distinct orthopyroxene groups and 10 distinct clinopyroxene groups from the $$TiO_{2}, Al_{2}O_{3}, Cr_{2}O_{3}$$, FeO, MgO, CaO, and $$Na_{2}O$$ contents. Names assigned to these groups convey their distinctive chemical features. Because many groups contain cases from both kimberlite and xenoliths, some kimberlite pyroxenes may derive from fragmented xenoliths. However from size alone, large discrete orthopyroxene crystals, discrete sub-calcic diopside nodules and low-Cr diopsides intergrown with ilmenite are apparently not xenolithic; nor are the minute diopside crystals growing in the kimberlite matrix. Pyroxene inclusions in diamonds and pyroxenes coexisting with diamond in eclogite and peridotite xenoliths range widely in chemical composition.