Muscovite
The Muscovite is a silver plated Minéral of color which is output in layers, of formula ( hydroxylated silicate of aluminum and potassium ).
(I=interfoliaire, O=octaédrique, T=tétraédrique).
Its form high pressure is called Phengite and, has as a formula with 0 ≤ X ≤ 1.
One passes from muscovite to phengite by the substitution of Tschermack: Its sodic equivalent is the Paragonite of formula: Muscovite, Phengite and Paragonite belong to the family of the white micas.
The Mica S are phyllosilicates or silicates in layer of structure EARLY with interfoliaceous cation. (cf diagram)
The tetrahedral layer (T) is made up of tetrahedrons of (Al can sometimes replace If) associated in layer. Each tetrahedron divides 3 of these 4 oxygen atoms with 3 other tetrahedrons. On this layer is an octahedral layer (O), known as sometimes brucitic. Tetrahedral apical oxygens are divided with the octahedral layer but the latter has also groupings OH. This octahedral layer can be tri-octahedral (filling by divalent cations) or di-octahedral (filling to the 2/3 by trivalent cations such as Al). Lastly, between each stacking of structure EARLY a cation resides.
In the case of muscovite, the layer T is made up of , the layer O of (dioctaedric layer O) and the interfoliaceous cation I is K+.
Phengite is a good pressure gauge which there existed at the time formation. Indeed, more the pressure is raised, more substitution of Tschermack takes place and more its content silicon increases.
Muscovite is enriched out of aluminum compared to biotite, its presence in the granites is a crustal proof of anatexie.
Layer
Muscovite often meets in the plutonic rocks (Granite, Pegmatite) and in the metamorphic rocks (Gneiss, Micaschiste). One finds also muscovite like secondary mineral in the faded rocks (Séricite)
Use
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