An unusual pyroxene, melilite, and iron oxide mineral assemblage in a coal-fire buchite from Buffalo, Wyoming

Near-surface combustion of the Healy coal seam near Buffalo, Wyoming, baked and partially fused a 20-m-thick overlying sequence of sandstone, siltstone and shale producing a multi-coloured vesicular rock resembling slag (buchite). This coal-fire buchite is highly heterogeneous and consists largely of clinopyroxenes, melilites and oxides, with minor glass. The pyroxenes are unusually rich in Al and Fe3+, and the Fe3+-rich melilites and oxides have chemical compositions heretofore unreported in nature.