Mica

The micas are an important group of minerals. They represent the classic phyllosilicate mineral and are usually the first minerals to be thought of from this subclass of the Silicates Class. Micas are significant rock forming minerals being found in all three rock types: igneous, metamorphic and sedimentary. Because thin flakes of mica are generally flexible and brittle, it is surprising how resistant and durable mica crystals can be in withstanding high temperatures and pressures in metamorphic regimes as well as the punishment of erosional environments. The term "mica" is so familiar to the general public that it is often considered a mineral in itself. Of course it is actually a group of minerals and most people who are knowledgeable about minerals know the three most common mica minerals: muscovite, biotite, and lepidolite and perhaps a few of the less common micas glauconite, paragonite, phlogopite and zinnwaldite. The Mica Group is actually a rather large group of minerals with over 30 members.

Block and sheet mica are used primarily for electrical and electronic applications where the combination of high dielectric strength, uniform dielectric constant, low power loss, high electrical resistivity, low temperature coefficient, high temperature resistance, chemical resistance, transparency, and ease of fabrication make it an excellent material of choice. In the 1800s the major use for sheet mica was in the manufacture of stove windows, shades for open flame lamps, and for furnace viewing glass. Beginning in the 1890s, the electrical insulating properties of mica became important and large quantities of sheetmica began to be used to manufacture commutator segments for electric motors and generators, in electric irons, toasters, fuse plugs, radio tubes, airplane spark plugs, condensers, capacitors, telephone equipment, radar components and a variety of other electrical and electronic equipment. Currently, the major uses for sheet mica are (Tanner 1994):

• Microwave Windows: Sheet mica can be fabricated into windows having excellent mechanical strength and low power loss using low temperature pressing methods.
• Condenser Mica: Mica has an average dielectric constant of 7, which makes it one of the most dependable types of insulators for all types of electronic applications. Read more . . .