Minerals in coals from the Changxing Mine of eastern Yunnan, southwestern China, were investigated using low temperature ashing plus X-ray diffraction (LTA + XRD), optical microscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM-EDX). The results show that minerals in the Changxing coals include mixed-layer illite/smectite (I/S), quartz, kaolinite, dolomite, Mg-bearing siderite, anatase, ammonium illite, K-illite, calcite, and chamosite, as well as minor amounts of hematite, paragonite. K-feldspar, and an Al-hydroxide mineral (gibbsite?). The Changxing coals are typically rich in mixed-layer I/S, accounting for an average of 47.2% in their low temperature ashes. Mixed-layer I/S occurs mainly in two types: (1) lentoid as thin beds, and (2) fractures- or cells-fillings. The Type 1 is of terrigenous detrital origin and probably related to the weathering products of the Emeishan basalt while the Type 2 is of epigenetic origin and precipitated from hydrothermal fluids of a mafic magma intrusion. The high K and poor Na in the Type 1 mixed-layer I/S indicate that it is in a higher evolution stage than the Type 2. Ammonium illite, K-illite, and paragonite are probably products of dissolution and recrystallization of mixed-layer I/S, while Mg-bearing siderite and partly chamosite are related to the Fe, Mg, Al, and Si released from the evolution of mixed-layer I/S. (C) 2012 Elsevier B.V. All rights reserved.