The extraction and utilization of coal inevitably lead to the generation of significant solid waste, including coal gangue. This byproduct is rich in kaolin mineral resources, and their effective utilization presents a critical strategy for the management of such a bulk solid waste, offering substantial environmental and economic benefits. The processing methodologies are often hindered by the inherent mineralogical properties of the materials. Kaolinite minerals are central to the chemical reactivity in calcined coal kaolin clay, the content and characteristics of kaolinite can vary significantly in different coal kaolin sources due to the diversity in coal-forming geological conditions. It is thus necessary to clarify the mineralogical properties of kaolinite from various sources for the innovative application of coal gangue. In this paper, a high-iron coal-series kaolin clay was analyzed. In addition, the impact of mineralogical properties on the thermal activation and preparation of calcined kaolin clay was also investigated.