Muscovite
Muscovite ( mica and clay ) is a very common mineral of the mica group within the mineral class of " silicates and Germanates ". It crystallizes in the monoclinic depending on the modification or the trigonal crystal system with the general chemical composition KAl2 [ (OH, F) 2 | AlSi3O10 ]. Structurally, it belongs to the layer silicates
Muscovite usually develops tabular, foliated, flaky crystals, but also massive aggregates in yellowish, brownish, reddish or greenish color. Even colorless crystals are known. Rare, but in meter-sized crystals, muscovite also occurs pseudohexagonal, that is the crystal form shows by twinning a seemingly hexagonal symmetry.
Its cleavage is perfect and the gap leaves are elastically flexible. This property, which he has in common with the dark mica ( biotite ), can give rock a slaty structure.
Etymology and history
Muscovite means in Russian as much as Moscow glass and was named in 1850 by James Dwight Dana so, since it is found in large aggregates grobblättrigen in Russia and was formerly used for window glazing and images of saints. Due to its heat resistance, it is also very good as a protective glass for oven window.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the muscovite belonged to the department of " layer silicates ( phyllosilicates ) ," where he along with seladonite the " celadonite - muscovite series ( Phengite ) " with the system no. Formed VIII/H.10 and the other members Aluminoseladonit, Boromuskovit, Chromphyllit, Chromseladonit, Ferro - Aluminoseladonit, Ferroseladonit, Ganterit, Nanpingit, paragonite, roscoelite and Tobelith.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the muscovite also in the department of " layer silicates ( phyllosilicates ) " a. However, this is further subdivided according to the crystal structure, so that the mineral according to its construction in the subsection " layer silicates ( phyllosilicates ) with mica sheets, composed of tetrahedral and octahedral nets " can be found where there is sole named the " Muskovitgruppe " with the system No. Forms 9.EC.15 and the other members Aluminoseladonit, Boromuskovit, celadonite, Chernykhit, Chromseladonit, Chromphyllit, Ferro - Aluminoseladonit, Ferroseladonit, Ganterit, Montdorit, Nanpingit, paragonite, roscoelite, Tainiolith and Tobelith.
The mainly common in English-speaking classification of minerals according to Dana assigns the muscovite in the department of " layer silicate minerals " one. Here he is as a member and namesake of the " mica group (muscovite - subgroup ) " with the system no. To find " layers of six-membered rings with 2:1 layers phyllosilicates " 71.02.02a within the subdivision.
Modifications and varieties
Muscovite is a collective term for the modifications:
- Muscovite - 2M1 - monoclinic prismatic - 2 / m ( C2h )
- Muscovite -1M, also muscovite - 2MD - monoclinic
- Muscovite -3T - trigonal
The following varieties are known so far
- Alurgit - red by the incorporation of manganese
- Astrolith - white to yellow
- Damourit - pseudomorphs after topaz or corundum
- Fuchsite - by a low chromium content ( 1-5 %), scaly, green iridescent aggregate
- Margarodit - contains sodium and calcium
- Mariposit - contains up to one percent of chromium
- Phengite - highly siliceous
- Pinite - pseudomorphs after cordierite
- Pinitoid - pseudomorphs after feldspar
- Sericite - Fine-grained or feinschuppiges muscovite or paragonite aggregate ( grain size < 0.1 mm)
Education and Locations
Muscovite is a major rock forming mineral and is formed by the metamorphosis especially in mica schist and gneiss, but also magmatic in granite or pegmatite, where it can form crystals of up to 5 meters and 85 tonnes, as among others in the " Inikurti Mine " at Nellore in India surfaced in. It comes in many acidic plutonic rocks and crystalline schists before, but not in volcanic effusions. Weathered it, the result is called by releasing potassium a clay mineral, illite or Hydromuskovit. Accompanying minerals occur among others in alkali feldspar and plagioclase, biotite, quartz, topaz and tourmaline.
Muscovite is found in many places around the world, with a total to date (as of 2013) are considered to be known around 13,000 localities.
In Germany they found the mineral, among others, in many places in the Bavarian Forest ( ground corn, Drachselsried, Vilshofen ), in the Eifel ( Ettringen, Niedermendig, Niederzissen), in Eppsteiner slate of the Taunus # Vordertaunus, in the Erzgebirge ( Ehrenfriedersdorf, Freiberg, Upper Lusatia ), in the Fichtelgebirge ( Troestau, White city), in the resin ( Bad Harzburg ) in Münchberger gneiss mass, in the Upper Palatinate Forest ( Waidhaus ), in the Odenwald ( Reichel home ), in the Black Forest ( Hornberg, Wittichen ), the winning country in the Spessart, in the Thuringian Forest ( Gottlob, Henneberg ) and in Vogtland ( Lengenfeld ).
In Austria muscovite previously could be found primarily in Carinthia ( mountain hut, Gurktaler Alps, Hohe Tauern ), Salzburg ( Nassfeldtal, Habachtal, Untersulzbachtal ), Styria ( Fischbacher Alps, Koralpe ) and Tyrol ( Kalstal, Zemmgrund, Zillertal ).
In Switzerland, the mineral Graubünden especially in the cantons ( front and rear Rhine Valley ), Ticino (Valle Maggia, Valle Leventina) and Wallis ( Binn valley ) was found.
Beautifully designed crystal specimens of up to 10 centimeters in size are also known from the pegmatites in Alabashka Murzinka ( Sverdlovsk Oblast ) in the Urals.
Almost transparent Muskovitscheibe with Hematite inclusions from Chandler's Hollow, Delaware ( Overall Size: 32.0 x 22.9 x 0.2 cm)
Smoky quartz and muscovite in microcline from the " Little Three Mine", San Diego County, California ( Size: 6.8 x 6.8 x 2.4 cm)
Crystal structure
Muscovite polytype crystallized in a monoclinic symmetry, referred to as muscovite 1M, muscovite 2M1 and 2M2 and muscovite in trigonal symmetry with the label muscovite 3T and triclinic symmetry designated muscovite 2A.
Use
Muscovite is due to its good thermal and electrical insulation an important raw material in the technical industry. Previously he was also often used for heat-resistant oven window and in Russia for glazing ( glass Moscow ).
Finely ground he serves (also with other types of mica ) as a filler and the inner reinforcing coating systems. Fillers based on muscovite mica having a wide range of particle sizes ranging from 0.001 mm up to 0.5 mm. In cosmetics, the Muscovite place along with the biotite used in lipsticks and other cosmetics to give a long lasting shine.
The variety Fuchsite (chrome - muscovite ) served in the painting as a green pigment and is known for its use in Native American art from Guatemala.