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Muscovite Mica: Mineral Information
With additional info on several other Mica varieties: Biotite, Clinochlore, Fuchsite, Lepidolite, Seraphinite and Zinnwaldite
Muscovite is the pure potassium mica.
Muscovite is colorless, and it has no impurities replacing elements in its crystal structure.
There are several muscovite mica varieties including lepidolite and fuchsite.
When muscovite occurs with natural green color due to chromium impurities replacing aluminum in the mica crystal structure is known as Muscovite Mica Information Topics:
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MUSCOVITE MICA PHYSICAL PROPERTIES
- Chemical composition of muscovite mica:
- Muscovite: KAl2(Si3Al)O10(OH)2
- Muscovite Mica Class: phyllosilicate
- Muscovite Mica Crystal System: monoclinic; 2m
- Muscovite Mica Crystal Habit: scaley, platy, micaceous, also compact massive. Distinct crystals are uncommon and are typically tabular with a book-like form with basal planes, showing a hexagonal or diamond-shaped outline. Prism faces are striated horizontally and frequently taper.
- Twinning: occaisional twinning on {110}, a twin axis in the {001} composition plane forms the complex mica twin.
- Muscovite Mica Specific gravity: 2.77-2.88
- Muscovite Mica Index of refraction: 1.552-1.616
- Muscovite Birefringence: .036-.049
- Pleochroism: muscovite is colorless
- Muscovite Mica Hardness: 2.5-4, hardness is greater perpendicular to the cleavage
- Color: colorless
- Muscovite Mica Luster: vitreous, pearly, metallic
- Muscovite Mica Transparency: translucent, transparent in thin sheets
- Muscovite Mica Cleavage: perfect basal cleavage
- Streak: white
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MUSCOVITE MICA BACKGROUND INFO
The micas are complex hydrous potassium-aluminum silicate minerals. There are more than 20 chemically distinct mica species with considerable variance in geologic occurance, but all have essentially the same crystal structure. The micas crystallize with a sheet structure, the sheets being held together by relatively weak bonds resulting in the perfect basal cleavage of the micas.
Muscovite is the pure potassium mica, containing no impurities. Muscovite is colorless.
There are several muscovite varieties.
Fuchsite
mica is a chromium rich variety of muscovite where
chromium cations substitute for some of the octahedral aluminum in the
muscovite crystal structure.
The chromium impurities in fuchsite are
responsible for its emerald green color.
Lepidolite mica is a lithian mica where an occaisional lithium cation substitutes for some of the octahedral and tetrahedral aluminum in the mica crystal structure.
Zinnwaldite is a lithian ferrous mica, where lithium and iron cations substitute for some of the octahedral and tetrahedral aluminum.
Biotite is the most common of the micas, containing iron and/or magnesium impurities substituting for octahedral aluminum.
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FUCHSITE MICA GEOLOGIC OCCURRENCE AND DIAGNOSTIC FEATURES
The micas have a very wide range of geological occurances. The many varieties of mica are distinguished by their chemical composition, some varieties occuring only in very specific geological settings while others have more widespread occurances.
Muscovite mica also is a very widespread and common rock forming mineral.
In igneous rocks, muscovite is characteristic of granites, and it commonly occurs in granitic pegmatites together with quartz, albite and microcline with accesory minerals topaz, aquamarine and other beryls, kunzite and tourmaline in a variety of colors with the most common being black tourmaline crystals.
In metamorphic rocks muscovite is very common especially in some mica schists where it is the dominant mineral.
In some mica schists and quartzites, muscovite crystallizes with a significant percentage of chromium impurities resulting in the emerald green colored variety fuchsite.
Muscovite also commonly occurs as sericite, a fine-grained alteration product of other minerals.
When microscopic flakes of fuchsite crystallize inside of quartzite giving it a green color, the rock is known as green aventurine quartz which is a popular lapidary material for making natural color green aventurine jewelry.
Lepidolite mica occurs mainly in granitic pegmatites associated with
quartz, micrcoline,
albite, amblygonite and occaisionally the gem varieties of
tourmaline and spodumene.
Zinnwaldite mica occurs mainly in granite pegmatites and high temperature
hydrothermal veins.
Biotite mica is the most common of the micas, in fact it is the most common ferromagnesian mineral! It occurs in most igneous and metamorphic rocks and is commonly found in detrital sediments.
The micas are usually recognized by their perfect basal cleavage. Some mica varieties can be distinguished with reasonable certainty by their color; for example the green muscovite variety fuchsite and the lavender muscovite variety lepidolite.
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MUSCOVITE MICA HISTORY AND USES
The name mica was derived from the Latin micare which meant to shine. The name Muscovite was derived from the term muscovy-glass which it was previously known by because of its widespread use as a glass substitute in the old Russian state of Muscovy in the 14th century. The chromium-rich muscovite variety fuchsite was named after the German mineralogist Johann Nepomuk von Fuchs. Biotite was named after the French physicist J. B. Biot. The name Muscovite was derived from the term muscovy-glass which it was previously known by because of its widespread use as a glass substitute in the old Russian state of Muscovy in the 14th century. The chromium-rich muscovite variety fuchsite was named after the German mineralogist Johann Nepomuk von Fuchs.
Muscovite has a wide variety of uses as an insulating material in electrical equipment due to its strongly dielectric properties and to its good electrical resistivity and capacitance stability. Muscovite also has a low coefficient of expansion, and it has been used extensively because of its heat resisting properties. Muscovite and some other micas are used extensively in paints to increase weatherability and to reduce running. Muscovite is also used in the manufacture of wallpapers to give them a silky or shiny luster. Muscovite mica is also used in the manufacture of lubricants and in dry-powder fire extinguishers.
Impurities within sandstones commonly alter to mica during high grade metamorphism. If chromium is present, then the green colored muscovite mica variety fuchsite can occur disseminated throughout the quartzite matrix in parallel orientation giving it a green color and a spangled effect. This material is known as green aventurine quartz.
Aventurine rough has been worked by man into ornamental objects for thousands of years. Green aventurine quartz is a popular lapidary material today, showing an atractive natural green color when polished or when wet.
The astrological sign of muscovite is Aquarius, and the sign of biotite is Scorpio.
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MUSCOVITE METAPHYSICAL PROPERTIES
Muscovite is said to increase one's understanding and perception, and to enhance one's reflective abilities.
Biotite is said to enhance one's perception, allowing one to more clearly understand what is really happening in any situation.
Fuchsite is said to enhance the body's ability to heal itself, and to increase the effectiveness of other minerals that are being used in healing.
Lepidolite is said to be very soothing and to have a calming effect, relieving anxiety and tension. Lepidolite with rubellite tourmaline (try holding a rubellite tourmaline in lepidolite sphere) is said to bring happiness, joy and increased vitality, and to inspire love.
For more in-depth metaphysical information, see our Metaphysical Books section.
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This is the end of our Muscovite Mica Factsheet and Information page.
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Last Updated: June 9, 2020
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