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Author: Admin | 2025-04-27
Mica has been resolved.[14] View of tetrahedral sheet structure of mica. The apical oxygen ions are tinted pink. View of trioctahedral sheet structure of mica. The binding sites for apical oxygen are shown as white spheres. View of trioctahedral sheet structure of mica emphasizing octahedral sites View of dioctahedral sheet structure of mica. The binding sites for apical oxygen are shown as white spheres. View of dioctahedral sheet structure of mica emphasizing octahedral sites View of trioctahedral mica structure looking at surface of a single layer View of trioctahedral mica structure looking along sheets Chemically, micas can be given the general formula[15]X2Y4–6Z8O20(OH, F)4,in whichX is K, Na, or Ca or less commonly Ba, Rb, or Cs;Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.;Z is chiefly Si or Al, but also may include Fe3+ or Ti.Structurally, micas can be classed as dioctahedral (Y = 4) and trioctahedral (Y = 6). If the X ion is K or Na, the mica is a common mica, whereas if the X ion is Ca, the mica is classed as a brittle mica.Muscovite[16]ParagoniteBrittle micas:Margarite[17]Trioctahedral micas[edit]Common micas:Biotite[16]LepidolitePhlogopiteZinnwalditeBrittle micas:ClintoniteInterlayer-deficient micas[edit]Very fine-grained micas, which typically show more variation in ion and water content, are informally termed "clay micas". They include:Hydro-muscovite with H3O+ along with K in the X site;Illite with a K deficiency in the X site and correspondingly more Si in the Z site;Phengite with Mg or Fe2+ substituting for Al in the Y site and a corresponding increase in Si in the Z site.Sericite is the name given to very fine, ragged grains and aggregates of white (colorless) micas.Occurrence and production[edit]Mica embedded in metamorphic rockMica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites.[6]The
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