Origin of colour after firing feldspar-quartz raw material from the Sobotka region \(Lower Silesia, SW Poland\)

The article presents the studies of feldspar-quartz raw material from deposits in the Strzegom-Sobotka massif (Lower Silesia, SW Poland). The goal of this paper was to establish the causes of colour variation of samples after firing at 1200C. The scope of research encompassed among others a detailed chemical analysis of raw material and Mössbauer studies of two selected samples, as well as measurements of colour parameters after firing (L*, a*, b*). The chemical analysis revealed that the samples of darkest colours are characterized by the highest contents of: Fe2O3, MnO, Th, U, Ce, Nd. The Mössbauer studies demonstrated the quantitative predominance of Fe over Fe in the sample of relative darker hue, while its spectra parameters suggest that Fe is located in octahedral coordination that can result in cold blue tint. Ions Fe, occupying probably the tetrahedral sites, prevail in the other analysed sample, which probably causes its warm, reddish shade. The above-mentioned examinations lead to the finding that colour of analyzed samples after firing originates from ions of transition elements of various valence states and coordination (especially iron), as well as some REE and actinides.