True and brittle micas: composition and solid-solution series
| Autor: | Milan Rieder, G. Tischendorf, H. J. Forster, B. Gottesmann |
|---|---|
| Přispěvatelé: | 4.2 Inorganic and Isotope Geochemistry, 4.0 Chemistry and Material Cycles, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum |
| Rok vydání: | 2007 |
| Předmět: |
010504 meteorology & atmospheric sciences
Annite Chemistry Muscovite Mineralogy FEAL 550 - Earth sciences Crystal structure engineering.material 010502 geochemistry & geophysics 01 natural sciences Crystallography Octahedron Geochemistry and Petrology engineering Phlogopite Mica 0105 earth and related environmental sciences Solid solution |
| Zdroj: | Mineralogical Magazine |
| Popis: | Micas incorporate a wide variety of elements in their crystal structures. Elements occurring in significant concentrations in micas include: Si, IVAl, IVFe3+, B and Be in the tetrahedral sheet; Ti, VIAl, VIFe3+, Mn3+, Cr, V, Fe2+, Mn2+, Mg and Li in the octahedral sheet; K, Na, Rb, Cs, NH4, Ca and Ba in the interlayer; and O, OH, F, Cl and S as anions. Extensive substitutions within these groups of elements form compositionally varied micas as members of different solid-solution series. The most common true K micas (94% of almost 6750 mica analyses) belong to three dominant solid-solution series (phlogopite–annite, siderophyllite–polylithionite and muscovite–celadonite). Theirclassification parameters include: Mg/(Mg+Fetot) [=Mg#] formicas with VIR >2.5 a.p.f.u. and VIAl tot/(Fetot+Li) [=Fe#] formicas with VIR >2.5 a.p.f.u. and VIAl >0.5 a.p.f.u.; and VIAl/(VIAl+Fetot+Mg) [=Al#] formicas with VIR 0.7 a.p.f.u., or, fortr ansitional stages, 0.3–0.7 a.p.f.u. Some true K mica end-members, especially phlogopite, annite and muscovite, form binary solid solutions with non-K true micas and with brittle micas (6% of the micas studied). Graphical presentation of true K micas using the coordinates Mg minus Li (= mgli) and VIFetot+Mn+Ti minus VIAl (= feal) depends on theirclassification according to VIR and VIAl, complemented with the 50/50 rule. |
| Databáze: | OpenAIRE |
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