Etymology and History of Mica
Mica gets its name from the Latin word Mica which literally means "a crumb" and is assumed to be influenced by the word Micare, meaning "To shine or glitter. Mica is known as Abharak or Abhrak in Hindi. Mica has been used in India since ancient times. Finely powdered Mica have been utilised for various applications, like for decoration. During the Indian festival of Holi, coloured Gulal or Abeer used by Hindus in various parts of the country consists of fine minute crystals of mica. The majestic Padmanabhapuram Palace, 65 km from Trivandrum in India, has coloured mica windows.
Types of Mica
There are two types of Mica available in the world, dioctahedral and trioctahedral mica. In Trioctahedral mica, the most common types found are Muscovite, Zinnwaldite, Biotite, Lepidolite, and Phlogopite. Where as Clintonite is Brittle mica.
Availability of Mica
Mica is widely available and distributed in sedimentary, metamorphic and igneous regimes. Large sized mica crystals, utilised for various purposes, are usually mined from granitic pegmatites. In India, Mica is widely available in Karnataka, Bihar, Kolkata, Rajasthan, Gudur and Andhra Pradesh. Hazaribagh, Gaya and Mungerdistricts of Bihar account for a huge proportion of the total production. These districts lie on the northern fringe of Chota Nagpur Plateau. The remaining half is evenly divided between Nellore District in Andhra Pradesh and Bhilwara District in Rajasthan. Mica is also mined in small quantities in Udaipur, Sikar, Tonk and Ajmerdistricts of Rajasthan. Moreover, a small proportion is also mined in small quantity in Nilgiri district. Production has been worsening due to artificial replacements.
In India, mica belt is located along the northern fringe of the Bihar Plateau as includes parts of Hazaribagh and Gaya districts. Mica belt generally occurs in the veins of the metamorphic rocks. The mica belt in this region runs in the east-west direction. Giridih, Domchanch and Kodarma are the principal collecting centres where it is processed. This particular mica belt produces more than half of the total mica production of the country.
Properties of Mica
Muscovite and Phlogopite are the most commercially significant micas that have several uses. Mica's value is based on several of its unique physical properties. The crystalline structure of mica forms layers which can be split into thin sheets. The sheets are usually chemically inert, elastic, dielectric, hydrophilic, flexible, insulating, platy, lightweight, reflective, resilient, refractive, and range in opacity from transparent to opaque. Due to the unique combination of physical, chemical and thermal properties, low power loss factor, dielectric constant and dielectric strength, Mica is precious in the electrical industry. The properties like low power loss factor and dielectric constant make mica ideal for use in condensers, the basic function of which is to store electrostatic energy in the dielectric field momentarily perhaps one-Millionth part of a second and then to re-deliver it with the minimum possible loss. The quality of Mica for commercial use depends largely on the amount of staining, air inclusions, the degree of flatness, and the colour.
Uses of Mica
Sheet mica is utilised in numerous electrical and electronic appliances in different shapes and sizes. Mica is used in equipments like condensers, sheostats, transformers, electronic tubes, and radio and radar circuits as an insulating material. Mica is also used in the form of washers, discs, tubes and plates. Nowadays mica is finding increasing use in equipment that encounters very high temperatures like rockets, missiles and jet engine ignition system. Hlogopite is used in spark plugs. Mica films are used in alternate layers of binding materials like shellac, alkyl, or silicon resin and then pressed and baked.
In the electronic-field, natural mica is mainly used in the manufacture of capacitors such as bridge-spacers in electronic valves and as panel-board where heat-resistance and low-loss properties at high frequencies are required. The scrap mica obtained during the processing of crude mica, is utilised in the manufacture of mica bricks for heat insulation, mica powder for use as filler in rubber goods, plant, lubricant and to some extent in plastic industries. It is also used in the manufacture of roofing material, welding rod, wall-paper, lamp chimneys, shades etc.
Small quantity of this mineral resource of the country is also used for the production of mica powder and mica bricks. Mica powder is used in the production of rubber goods and paints. Mica bricks are used as an insulating material in steel and thermal power plants and petroleum refineries. Interestingly, the production of mica depends on foreign demand to a great extent. Huge amount of Mica in India is exported. Countries like United States, Japan and United Kingdom are the major buyers of mica.
Substitutes of Mica
Perlite, diatomite and vermiculite may be substituted for ground mica when utilised as filler. Ground synthetic fluorophlogopite may replace natural ground mica for uses that require thermal and electrical properties. Many materials can be substituted for mica in numerous electrical, electronic, and insulation uses, like cellulose acetate, acrylate polymers, fishpaper, fiberglass, phenolics, nylon, polyester, polycarbonate, styrene, vulcanized fiber and vinyl-PVC. Mica paper, obtained from scrap mica can be substituted for sheet mica.