Mica

—A mineral substance, distinguished by nearly perfect cleavage, largely used for insulating purposes because of its excellent properties of insulation and durability. Mica is capable of being split into elastic plates - of extreme thinne . It is either colorle or ees some shade of light brown, gray, smoky rown, black, and occasionally green or violet. It is generally more or le transparent. Mica po e es an electrical resistance of 84,000,000,000,000 ohms per cubic centimeter and is an ideal insulator, except for the fact that it frequently contains impurities that reduce its dielectric efficiency, and also when used as insulation for spark plugs, owing to its laminated structure, oil and gas may be forced by the pre ure of compre ion between the sheets composing the insulating sheath, thus, in time, producing short circuiting of the current.