The studies of granitoids from the Sobótka region in light of theories of the origin of colour in minerals

What is it about?

The article presents the results of the studies of 19 feldspar-quartz raw materials samples, coming from deposits located in the Sobótka region, in light of four distinct physical theories explaining mechanisms for creating the colour of minerals. This is a successive stage of research carried out by the author on reasons for colour variation of samples after firing at 1200oC. This step encompassed a detailed chemical analysis for main and trace elements contents of all the investigated samples as well as Mössbauer studies of two of them.

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Why is it important?

The chemical analysis reveals that the darkest samples are characterised by the highest contents of the following colouring compounds and elements: Fe2O3, MnO, Th, U, Ce, Nd, and V, accompanied by a relatively low amount of TiO2. The Mössbauer studies demonstrated the quantitative predominance of Fe2+ over Fe3+ in the sample of a relatively darker hue with a high Fe2O3 content, while its spectra parameters suggest that Fe2+ is located in octahedral coordination that can result in a cold blue tint. Cations (located probably in the tetrahedral position) prevail in the other analysed sample that contain less Fe2O3 and a relatively high content of TiO2, Ce, and Nd, Fe3+. This probably causes a warm, reddish shade of the sample.