Individual grains of calcian fayalite and ferroan kirschsteinite, as well as fayalite-kirschsteinite intergrowths are observed in the groundmass of basic crystallised melts, o parabasalts, from burned spoil-heaps of the Chelyabinsk brown-coal basin. Exsolved fayalite and kirschsteinite rims surround the grains of fayalite and early Mg-Fe olivine. The chemical study of the olivines has shown that during their crystallisation they were becoming enriched in fayalite and larnite and depleted in forsterite. The intergrowths of ferroan kirschsteinite (> 20 wt.% of CaO) and calcian fayalite (< 8.5 wt.% of CaO) are the exsolution products of an initially homogeneous Ca-Fe olivine with CaO > 8.5 wt.%. The exsolution temperatures were estimated to 980–800 °C. The main reasons for the appearance of the Ca-Fe olivine in the parabasalts are the composition of the initial melt enriched in FeO and CaO, fractional crystallisation resulting in further enrichment in iron of the residual low-silica melt, and reducing conditions during olivine crystallisation and exsolution.

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