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Minerals and rocks
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
Muscovite (K2Al4Si6Al2020[OH]4) is a light-coloured member of the mica group, which has a similar atomic structure and crystal form to biotite. It occurs in silica-rich igneous rocks as a ‘wet’ mineral which crystallises at a late stage, together with quartz. It is particularly common in veins of coarse granite-like rock (pegmatite) and may be mined from them to be used as sheets having good thermal or electrical insulation. It is also present in many sedimentary and metamorphic rocks. Like most other micas, muscovite alters to clay minerals, particularly illite and montmorillonite. Sericite is a term used to describe fine-grained white micas. Such white micas are chemically similar to muscovite.
Metamorphism
Published in Aurèle Parriaux, Geology, 2018
This mineralogical transformation is confined to clays; it causes the formation of small embryonic white micas called sericite. Mica gives the rock a lustrous appearance. The rock does not appear to be crystalline. It breaks up into thin plates, is often black in color (slate), and is perfectly suitable as roofing material (Fig. 11.16).
Comparison and evaluation of alumino-silicate samples as a dual source of alumina and potash values
Published in Canadian Metallurgical Quarterly, 2023
In this study, the non-bauxite aluminosilicate samples (mica, sericite, diaspore, feldspar) are explored to extract aluminum and potassium values. Mica has layered muscovite sheets; sericite comprises fine-grained muscovite and illite phases with quartz present as a major impurity. In contrast, diaspore contains illite as a major phase with diaspore. Direct HCl leaching of samples yielded 1-5% Al and K dissolution. The mechanical and thermal activation was evaluated before HCl leaching for structural dissociation and metal dissolution. Mica and sericite were found amenable to the milling pretreatment, and 8 h milling before 2 M HCl leaching yielded 72-82% Al and 63-75% K extraction.