Clinopyroxenes of the coesite eclogite of southern Norway, the graphite eclogite of the Münchberger Gneisgebietes of Bavaria, and kimberlitic Group I eclogite of South Africa; and chromian diopside of South Africa were examined. Accommodation of potassium in clinopyroxene is generally thought to require special pressure conditions, e.g. the clinopyroxenes included in diamond; and possibly involves distorted low symmetry eightfold coordination cation polyhedra M2. The clinopyroxenes of various origins and potassium contents provide a basis for comparison. The Bavarian cpx is below 0.1 wt%, mostly below 0.05%, in K20. The Group I eclogite cpx is up to 0.5% K20, and the Norwegian cpx is in between and close to the lower end. Correlation between the K20 content and cell parameters is inconclusive for the omphacites examined.
Multichannel micro Raman spectrum of single crystal Bavarian omphacite has principal bands at 1018.6 cm-1 (interpreted as non-bridging oxygen symmetric stretching mode), 675.2 cm-1 (bridging oxygen); and bands of smaller intensities. The corresponding bands of Group I omphacite are slightly lower in frequency, 1013.7 cm-1 and 671.8 cm-1.
If the bands near 670 cm-1 are associated with ns(T-0-T) in the cpx chains, and the shift is signifikant, the T-O-T intertetrahedral angle of Group I K-omphacite can be larger than that of Bavarian omphacite. Accommodation of K in these omphacites may not involve signifikant increase in the overall cell volume, but possibly adjusted T-O-T angle.