A suite of minerals found in coals were analysed using an improved ash fusion test, These minerals were quartz, potassium feldspar, sodium feldspar, calcite, dolomite, siderite, pyrite, kaolinite, illite and apatite. Each specimen was also analysed by XRD as an "as-received" specimen, an 800 degrees C product and a 1600 degrees C product. These results allowed evaluation of the applicability of the improved ash fusion test for determination of chemical changes occurring in the ash fusion furnace. Phase changes were observed in the improved ash fusion test for the Na feldspar, siderite and pyrite specimens. K feldspar movement could, in part, be related to phase changes. The complex reactions occurring in the illite and kaolinite specimens limited the interpretation. The calcite and dolomite specimens movement was dominated by reactions of calcite, lime and portlandite. The quartz and apatite specimens were relatively inert. These results indicate that the improved ash fusion test can provide a link between the various standard ash fusion tests and analytical tools such as XRD to provide enhanced understanding of the processes occurring in the ash fusion furnace.