from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun A potassium aluminum silicate mineral, KAl2(AlSi3O10)(OH)2, the most common form of mica, which ranges from colorless or pale yellow to gray and brown, has a pearly luster, and is used as an insulator.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun mineralogy A pale brown
mineralof the micagroup, being a basic potassium aluminosilicatewith the chemical formula K Al2( Si3Al) O10(O H, F)2; used as an electrical insulatoretc.
from The American Heritage® Dictionary of the English Language, 4th Edition
from Wiktionary, Creative Commons Attribution/Share-Alike License
The mica group of minerals includes: biotite, muscovite, lepidolite, and phlogopite.
In 1850, James Dwight Dana formally named this mineral muscovite based on the Latin term.
The two micas used as a commodity are: brown mica or phlogopite which contains iron and magnesium; and the "reddish, green, or white (or clear) mica" or muscovite which contains potassium and aluminum.
Very large sheets or crystals of muscovite form in a pegmatite.
In teaching geology, micas - especially muscovite - makes an impact I can see through it!
These layers can be seen in muscovite mica specimens because it can be split (mineralogists call this feature cleavage) into very thin, flexible, transparent layers.
Muscovite was always a hit with people in my general classes, especially when I wold tell the girls that some of the "minerals" in their makeup were muscovite/micas!
In the metamorphosed Thunderhead Sandstone it was found that at the staurolite isograd, the boundary between the garnet and staurolite zones, the mineral chlorite disappears from the rocks and muscovite decreases sharply, whereas staurolite appears and biotite becomes more abundant.
It seems to be a true muscovite, and is seldom marred by magnetic markings or crystalline inclusions that would interfere with its industrial use.
The proportions of the constituent minerals which form granite, according to Prof. Phillips, are twenty parts of potash feldspar (orthoclase), five parts of quartz, and two parts of potash mica (muscovite), and a survey of Mr. Wilson's quarry exhibits these approximate relations with surprising force.