Evaluation of limonite concretions by chemical and mineralogical composition, their formation model

The formation conditions of limonite, often iron-oxide and hydroxide containing mineraloids can be related to the crystallisation process of iron oxides minerals in weathering crust sedimentation. Iron oxides (goethite, hematite) and their various admixtures form lithification compounds. The research involved the analysis of limonite concretions and their thin sections, composition analysis and interpreting the conditions of formation. Thin sections were examined by the difference in the formation of limonite ageing, colour, interpreting composition and colour range of tones depending on available chemical elements during their formation process, as well as granular composition. Two limonite formation models were interpreted – surface crust formation on top of other mineral aggregate (by evaporating mineral water solution), as well as the formation of limonite in the process of alluvial deposit. It was concluded, that the variation of the limonite tint depends on the degree of iron oxidation state, admixture of elements, fine grain practices and the environment of the formation, including the amount of water available. The mineral composition of limonite can be homogeneous or with polyphase structure, without noticeable change in colour, at the same time, the materials of relatively uniform mineral composition can be cardinally different in colour range.