Mineral microspherules in Chinese coal and their geological and environmental significance

Studies of finer-grained minerals in coal have great significance for both geology and the environment. Eleven coal samples of different rank were collected from different regions in China, and mineral microspherules were identified in these samples by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). The microspherules usually occur as regular spheres with smooth surfaces, and have an average size of less than 5 mu m in diameter. Most microspherules are colloidal in origin, and include phases such as Fe-sulfides, glauconite, Fe-hydr/oxides, calcium oxalate and allophane. Allophane is a product of colloidal Al2O3 and SiO2, which, as a precursor of kaolinite, exists ubiquitously in the coals, as does kaolinite. Some microspherules, such as garnet and sphene, are mainly derived from detrital sources, and a few microspherules probably result from volcanogenic ash and/or from cosmic dust. Ultrafine Na-bearing minerals were also found in the coals. Such micro, sub-micro, and ultrafine minerals in coal may play an important role in the formation of ultrafine coal fly ash particles. (C) 32011 Elsevier B.V. All rights reserved.