Potassium in Clinopyroxene Inclusions from Diamonds

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Science  08 Feb 1991:
Vol. 251, Issue 4994, pp. 652-655
DOI: 10.1126/science.251.4994.652


Analytical transmission electron microscopy, electron microprobe analyses, and singlecrystal x-ray diffraction data support the conclusion that high potassium contents, up to 1.5 weight percent K2O, of some diopside and omphacite inclusions from diamonds represent valid clinopyroxene compositions with K in solid solution. This conclusion contradicts the traditional view of pyroxene crystal chemistry, which holds that K is too large to be incorporated in the pyroxene structure. These diopside and omphacite inclusions have a high degree of crystal perfection and anomalously large unit-cell volumes, and a defect-free structure is observed in K-bearing regions when imaged by transmission electron microscopy. These observations imply that clinopyroxene can be a significant host for K in the mantle and that some clinopyroxene inclusions and their diamond hosts may have grown in a highly K-enriched environment.

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