The dictionary defines mica as "A class of silicates having a prismatic angle 120°, eminently perfect basal cleavage, affording thin tough laminae or scales, colorless to jet black, transparent to translucent, of widely varying chemical composition, and crystallising in the monoclinic system".
In brief, mica is a generic term applied to a group of a complex aluminosilicate minerals having a sheet or plate like structure with different chemical compositions and physical properties. All micas from flat six-sided monoclinical crystals with a remarkable cleavage in the direction of the large surfaces, which permits them to split easily into optically flat films, as thin as one micron in thickness. When split into thin films, they remain tough and elastic even at high temperature.
What makes micas so important to command such a unique position? Because it had been gifted with exceptional values. It possesses some of the most outstanding combination of chemical, physical, electrical, thermal and mechanical properties, which are not found in any other product.
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Physical Properties:
Mica is transparent, optically flat, easily split able into thin films along its cleavage, colourless in thin sheets, resilient and incompressible.
Chemical Properties:
Mica is a complex hydrous silicate of aluminum, containing potassium, magnesium, iron, sodium fluorine and/or lithium and also traces of several other elements. It is stable and completely inert to the action of water, acids (except hydro-fluoric and concentrated sulphuric) alkalies, conventional solvents, oils and is virtually unaffected by atmospheric action.
Electrical Properties:
Mica has the unique combination of great dielectric strength, uniform dielectric constant and capacitance stability, low power loss (high Q factor), high electrical resistivity and low temperature coefficient and capacitance. It is noted for its resistances to arc and corona discharge with no permanent injury, and has little or no effect when exposed to electronic radiation dosages up to 1018 nvt. Thus maintaining its a-c dielectric material when exposed to the oxidizing action of electrical discharges either on the surface or within internal gas spaces in built-up mica insulation.
Thermal Properties:
Mica is fire proof, infusible, incombustible and non-flammable and can resist temperatures of 600°C to 900°C (1112°F to 1652°F) depending on the type of mica. It has low heat conductivity, excellent thermal stability and may be exposed to high temperatures without noticeable effect.
Mechanical Properties:
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 withstand great mechanical pressure perpendicular to plane but the lamination has cleavage and can be easily split into very thin leaves.