Chrome-rich garnets from the kimberlites of yakutia and their parageneses |
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Authors: | N V Sobolev Yu G Lavrent'ev N P Pokhilenko L V Usova |
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Institution: | (1) Siberian Division of the USSR Academy of Sciences, Institute of Geology and Geophysics, Novosibirsk, USSR |
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Abstract: | The chrome-rich magnesian garnets (6.6–18.9% Cr2O3) of kimberlitic concentrates and some peridotite xenoliths contain variable admixtures of CaO: from 0.69 to 26.0% (1.7–72% Ca-component). All the garnets both in respect of Ca and Cr-contents make up a continuous series.The variability in the Ca-content is caused by differences in paragenesis. Most of the Ca-poor pyropes are related to a paragenesis without clinopyroxene (mostly dunitic). Garnets rich in calcium are related to a paragenesis without entstatite. All the parageneses listed are of an ultramafic type, i.e. contain magnesian olivine. The solubility of knorringite—Mg3Cr2(Si3O12)—in kimberlitic garnets is possibly limited by pressure and does not exceed 50–60% mol. |
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