Mica is a generic term applied to a group of rock-forming complex aluminosilicate minerals having a sheet or plate like structure with varying chemical composition and physical properties. Crystals of Mica are characterised by highly perfect basal cleavage in the direction of large surfaces permitting it to split or delaminate into extremely thin and flat films.
Mica possess some of the most exceptional and outstanding blend of properties rarely found in any other product commanding a unique position :
PHYSICALLY : Mica is flexible, transparent, optically flat, reflective, refractive, colourless in thin sheets, easily splittable into thin films along its cleavage, resilient and incompressible.
CHEMICALLY : Mica is tolerant and completely inert to the action of water, acids (except hydro-hydrofluoric acid and concentrated sulphuric acid), alkalies, bases, mineral oils, conventional solvents and chemical influence. Virtually unaffected by atmospheric action and weathering.
ELECTRICALLY : Mica has distinctive combination of great dielectric strength, uniform dielectric constant and capacitance stability, low power loss (high Q factor), high electrical resistivity, low temperature coefficient and superior insulating properties. It is noted for its resistance to arc and corona discharge with no permanent injury.
THERMALLY : Mica is fire proof, infusible, incombustible and non-flammable. It has low heat conductivity, remarkable thermal endurance and can be exposed to high temperatures without any noticeable effect.
MECHANICALLY : Mica is relatively soft and can be hand cut, machined or die-punched. It is flexible, elastic and tough having high tensile strength. It can easily sustain mechanical stresses and pressures.
Of the nine common varieties in the mica group of minerals, the two principal classes of Mica types of commercial importance are Muscovite and Phlogopite :
Muscovite Mica :
K Al2 (Al Si3 O10 )(OH) 2
Phlogopite Mica :
K Mg3 (Al Si3 O10 )(OH) 2
Muscovite Mica is a hydrous potassium aluminium silicate with a predominance of potassium. It has a vitreous lustre and ranges from colourless through browns to greens or reds. Muscovite Mica is transparent and harder than Phlogopite Mica having more widespread availability. It surpasses all mica due to its superior properties and is therefore identified as a necessary input for electrical and electronic applications as well as other industries. Vast exploitable reserves are found chiefly in India which produces and markets over 80% of the total global output of Muscovite Mica. Indian Muscovite Mica is considered the finest in the world. Deposits are also located in China, USA, Brazil and South Africa.
Phlogopite Mica is a hydrous magnesium aluminium silicate with a predominance of magnesium. It is commonly called as “Amber Mica” which varies in colour from light silver to dark brown or amber. Transparency is less than Muscovite Mica and its films are a bit cloudy. Phlogopite Mica is softer than Muscovite Mica but has greater heat resistance and thermal durability. It is preferred where a combination of high heat stability at high temperature is required. The deposits are chiefly found and mined in Madagascar, Canada, Sri Lanka and Russia.
Muscovite Mica may be divided into two color groups :
Colour ranges from an almost white through pink to a light ruby and into shades of brownish ruby and brown. It is produced in the Indian States of Jharkhand (formerly Bihar) and Rajasthan.
Ranges from light to pale green through yellowish and olive green to a dark green. It is produced in the Indian State of Andhra Pradesh.
Colour, as such, has less significant influence on quality. Both Ruby Mica and Green Mica are equally suitable under normal working conditions. Still, Ruby Mica is generally preferred since at elevated temperatures Green Mica displays erratic electrical characteristics. The structure of Green Muscovite is stable but less perfect as compared to Ruby Muscovite. Moreover, Ruby Muscovite is harder than Green Muscovite having excellent cleavage permitting it to be split into the thinnest desired film without the risk of cracking.
The global demand for mica products are enormous. India views herself as a recognized leader in enjoying inestimable and fathomless natural resources of muscovite mica. More than 80% of the world needs is catered by India earning a dominating position.
Exploration and exploitation is successfully carried by means of systematic vertical shaft and open cast mining. Although mica pegmatite occurrences have been recorded in many Indian locations, the principal muscovite mica deposits are chiefly found in the States of Jharkhand (formerly Bihar), Rajasthan and Andhra Pradesh.
The most important and famous center of major mining belt runs in the State of Jharkhand (formerly Bihar State) which produces the world's finest muscovite mica well known throughout the globe. The House of Gunpatroy Pvt. Ltd. and its subsidiary Shree GR Exports Pvt. Ltd. specialises in the production and exports of muscovite mica originating from the vast expanse of this region.
Various documentation have been made for the purpose of classification of Mica according to diverse sizes and qualities. The usual pattern of grading laid down by ISI, ASTM, NEMA, BSI, and DIN standards are followed in order that they may be accepted universally.
The quality determination of Sheet Mica is a matter of visual assessment and judgement. In this system of quality evaluation, emphasis is put on clarity, colour, flatness, hardness and freedom from spots, stains, air bubbles, visible inclusions and structural imperfections. The grading of size is done based on maximum usable rectangle area that a piece of sheet may yield.
The quality determination of Scrap Mica or Ground Mica is designed to estimate the degree and level of purity, whiteness, brightness, loss on ignition value, calcination capability, aspect ratio, bulk density and other facets of the specimen. The grading of particle or aperature size is set in terms of millimeters, inches, microns and mesh counts.
Quality of Mica is still a function of many variables and mutual understanding between the buyer and the seller is practiced for individual requirements.