Mica
A group of minerals having perfect basal cleavage and capable of splitting into thin laminae is called mica. Chemically they contain complex silicate of aluminium and alkalies with hydroxyl. They crystallize in monoclinic system. Some varieties may contain iron, magnesium, lithium and rearely fluorine, barium, manganese and vandium. Mica is found in pegmatites intruding mica schists. It is found to occur in book form in the pegmatites. The mode of formation of mica which is found in the form of small flakes to big slabs cleavable into the fine laminae is still the subject of active research. The presence of tourmaline crystals and decomposed felspar in the pegmatites shows the possibility of finding good quantity of mica.
Mica pegmatites have been found to occur in various shapes and sizes mostly occuring as lenses. They may occur as parallel veins, pipes or in massive form. It is difficult to ascertain when the vein will pinch out and hence the mining of mica is regarded as quite speculative. Also, the abrupt decrease in degree of mineralization and disappearence of mica from the working face is quite common. Pipe mica veins have been worked upto a maximum depth of 200 metres.
Industrial Uses
1) 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.
2) In the paint industry, ground mica is used as a pigment extender that also facilitates suspension due to its light weight and platy morphology.
3) Ground mica also is used in the well-drilling industry as an additive to drilling “muds.”
4) The plastic industry used ground mica as an extender and filler and also as a reinforcing agent.
5) The rubber industry uses ground mica as an inert filler and as a mold lubricant in the manufacture of molded rubber products, including tires.
6) 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.