A mineral of the mica group with an ideal
composition of KAl2(AlSi3)O10(OH)2. Sometimes it is referred to as a
white mica or potash mica. Like most micas, muscovite will form "books"
of mica crystals from which perfect, thin sheets can be peeled.
Muscovite is mined using underground mining. It is found in India,
Pakistan, Brazil, and the U.S.
Physical properties include specific gravity
2.76¨C2.88, hardness on the Mohs scale 2¨C2.5, and luster vitreous to
pearly. Thin sheets are flexible and may be colorless, with books
(thick crystals) translucent, yellow, brown, reddish, or green.
Muscovite occurs commonly in all the major rock types, in igneous rocks
(granites, pegmatites, and hydrothermal alteration products), in
metamorphic rocks (slates, phyllites, schists and gneisses), and in
sedimentary rocks (sandstones and other clastic rocks). As larger
flakes, muscovite is used as an electrical insulator, both for its
dielectric properties and for its resistance to heat. Ground muscovite
is used for fireproofing, as an additive to paint to provide a sheen
and for durability, as a filler, and for many other applications.
The name of muscovite comes from Muscovy-glass, a
name formerly used for the mineral because of its use in Russia for
windows. It is anisotropic, and has quite a high birefringence. Its
crystal system is monoclinic. If you crush this mineral¡ªno matter what
color it is¡ªit will form a colorless dust. Light will go through it
anywhere from clearly to blurrily. You might be able to see through
thin pieces of it. Muscovite would look glassy or pearly if you shined
a light on it. If you break this mineral, it will split into sheets or
layers.
Material Notes:
One cleavage direction. Occurrence: Igneous,
sediments, metamorphic. Very resistant to weathering. Muscovite is used
as an insulator because it is heat resistant. It is also used in
roofing, cosmetics, and paints. If you compared it to an equal volume
of water, it would be about average. If you held it in your hand, it
would seem to be about an average weight for its size.
Muscovite is also called white mica. The best way
to tell a mica is by the thin, transparent sheets that it cleaves into.
Large, clear plates of mica were once commonly used for windows, and
the productive Russian mica mines gave muscovite its name. Today mica
windows are still used in cast-iron stoves, but the greater use of
muscovite is as insulators in electrical equipment.
