## 1 Introduction  
The province of Teruel (NE Spain) has historically been an important coal mining area. In this area there are still abundant coal deposits, but coal mining has ceased in recent decades. In this paper, firing transformations [1] of mine spoils from the mined coal in the Utrillas-Escucha-Estercuel and Arino-Andorra regions are studied (Figure 1). The production of porcelain stoneware has experienced a considerable increase since its initial development in Italy in the late 1970s [2]. The valuation of these mine spoils can bring economic and environmental benefits [3]. However, this increase in manufacture was not accompanied by the necessary research to know the scope of the reactions that take place during the firing process of the ceramic pieces. It is worth noting the fact that the few publications that exist on the porcelain stoneware microstructure refer, above all, to issues of porosity and glass formation, without addressing the study of mullite formation and mineral quantification [1, 2]. Therefore, it was considered necessary to undertake an investigation that would allow knowing the mineralogical and microstructural evolution that porcelain stoneware undergoes during its firing process, as well as establishing the influence of the mullite crystalline phase formation on some properties as open porosity [2]. For production of porcelain stoneware, ball clays are required [2]. In the Spanish ceramic cluster, white ceramic clays have usually been imported from Ukraine, France, and the UK [3]. However, a greater knowledge of the mine spoils from the lignite mines in Teruel will allow their incorporation as new raw materials in the main ceramic companies [4; 5; 6]. The future use of these spoils will represent significant savings in production costs [3]. Mine spoils from the lignite mines associated with the Lignitos de Escucha (Escucha Lignites) and Arenas de Urtillas (Utrillas kaolinite sands) formations belong to the upper part of the Lower Cretaceous [3]. These mine spoils have a great importance in the ceramic cluster of Castellon (Spain), due to their possibilities for being used as ceramic raw materials These clayed mine spoils for industrial uses, on the basis on their mineralogy and chemical composition, can be classified as ball clays [1; 2; 3]. Some of these spoils are mined nowadays [4]. High-temperature mineral phases are generated in firing processes. Mineral phase transformations in a ceramic firing process have previously been described in literature [3; 7]. Previously, a powerful study was carried out on the determination of high-temperature mineral phases using these mine spoils as ceramic raw material [3]. The formation of mulite and other high-temperature phases were studied in 2015 [3]. However, it was not possible to quantify the mineral phases and the vitreous phase present for each firing temperature. There is no information in the literature about the quantification of high-temperature phase generation and amorphous phase formation from these mine spoils for different firing temperatures. Knowledge and quantification of high-temperature minerals generated using these mine spoils as raw materials is interesting in industrial processes for manufacturing stoneware and ceramic tiles, as well as refractory ceramics [5; 6; 7; 8]. In this work, for the first time, a quantification of mineral phase in the thermal transformations experienced by kaolinite mine spoils has been carried out. The ceramic industry has been shown to have great potential to absorb industrial waste [8; 9]. However, the commercial production of tiles from waste materials is very limited and, in some countries, non-existent. Some reasons include possible contamination by the waste used, the absence of relevant standards, and slow acceptance by industry and consumers.