Abstract

This contribution (i) chemically distinguishes the two carbonatites: sovite and alvikite, and (ii) presents new "average" (median) compositions for them. The best and most used average chemical composition for calciocarbonatite is that calculated by Woolley and Kempe in 1989, and it is shown here that this composition comprises two distinctively different compositions corresponding to those of sovite and alvikite. Sovite and alvikite are the coarse-grained and the medium- to fine-grained varieties, respectively, of calcite-carbonatite. It is proposed that the corresponding calciocarbonatites should be termed C1 calciocarbonatites and C2 calciocarbonatites, based on their chemical compositions. The distinction of the two lies, not in the major elements, but in the minor, trace- and rare-earth-element contents. Using a comprehensive database of post-1970 analytical data, the "average" compositions for C1 and C2 calciocarbonatites have been calculated. Instead of the arithmetical average, the arithmetical median has been calculated for each, since this gives truer estimates of the two compositions. It is believed that the two median compositions will enable C1 and C2 calciocarbonatites to be recognized.

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