Coal demineralization by Ca(OH)(2) leaching followed by dilute HCl washing was investigated primarily using reflected light microscopy and scanning electron microscopy with energy-dispersive X-ray analysis. A Hunter Valley coal was examined both in as-received form and after demineralization to various levels of residual ash. The major minerals in the original coal are quartz and clay. As the degree of Ca(OH)(2) leaching increased, mineral inclusions showed morphological changes and decreased in amount. Some clay was fairly readily removed by demineralization; other clay and quartz, in general, appeared to be less reactive. After Ca(OH)2 leaching, some residual inorganic inclusions were found to be rich in Ca and Si or in Ca, Si and Al; these inclusions may be leaching products. When no more than moderate amounts of CaO were added, the Ca-bearing components formed were effectively removed by acid washing. Under these circumstances, extensive leaching led to the removal of as much as 90% of the inorganic matter and few mineral inclusions were observable in the treated coal. With the addition of more CaO, some Ca consistently remained in the treated coal in a highly dispersed form.