Mica is a mineral name given to a group of minerals that are similar in their physical properties and chemical compositions. They are all silicate minerals, which means that chemically they all contain silica(SiO4). Mineralogists call micas sheet silicates because their molecules combine to form distinct layers. Mica crystals are six-sided. They are fairly light and relatively soft, at 2 to 4 on Mohs’ hardness scale for the univalent micas. Sheets and flakes of mica are flexible. Mica is heat-resistant and does not conduct electricity.
There are 37 different mica minerals. In addition to the silicate tetrahedrons in all micas,Purplelepidolite contains the elements potassium, lithium, and aluminum. Black biotite contains potassium, iron, and magnesium. 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.
Application Of Mica
Micas commonly occur as flakes, books, or sheets. Sheet muscovite (white) mica is used in electronic insulators (mainly in vacuum tubes), ground mica in paint, as joint cement, as a dusting agent, in well-drilling muds, and in plastics, roofing, rubber, and welding rods.
The principal use of ground mica is in gypsum wallboard joint compound, where it acts as a filler and extender, provides a smoother consistency, improves workability, and prevents cracking. In the paint industry, ground mica is used as a pigment extender that also facilitates suspension due to its light weight and platy morphology. The ground mica also reduces checking and chalking, prevents shrinkage and shearing of the paint film, provides increased resistance to water penetration and weathering, and brightens the tone of colored pigments. Ground mica also is used in the well-drilling industry as an additive to drilling “muds.”
Coarsely ground mica flakes help prevent lost circulation by sealing porous sections of the uncased drill hole. The plastic industry used ground mica as an extender and filler and also as a reinforcing agent. The rubber industry uses ground mica as an inert filler and as a mold lubricant in the manufacture of molded rubber products, including tires.
Sheet mica is used principally in the electronic and electrical industries. The major uses of sheet and block mica are as electrical insulators in electronic equipment, thermal insulation, gauge “glass”, windows in stove and kerosene heaters, dielectrics in capacitors, decorative panels in lamps and windows, insulation in electric motors and generator armatures, field coil insulation, and magnet and commutator core insulation. Mica is also used as segment plates between copper commutator sections to insulate copper from the steel; phlogopite mica is used because it wears at the same rate as the copper segments.
Sources Of Mica
Scrap and flake mica is produced all over the world. In the U.S., scrap and flake mica was produced in Arizona, North Carolina, South Dakota, Georgia, New Mexico and South Carolina. North Carolina’s production accounts for half of total U.S. mica production. The flake mica produced in the U.S. comes from several sources: the metamorphic rock called schist as a by-product of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. Canada, India, Finland, and Japan export flake mica to the U.S.The United States has limited sheet mica resources. U.S. mining of sheet mica is costly and labor costs are high. As a result, the U.S. imports more than half its sheet mica from India, but also from Belgium, Germany, China, and a few other countries.