The binding forces in one plane are quite strong, while the binding forces along the perpendicular plane are very weak. Because of this it has a distinct layered structure and it is possible to split or cleave mica into very thin, optically flat, sheets. For capacitors, mica sheets in the range 0.025 0.125 mm, or even thinner, are used. While there are many types of mica, only six or so are common rock-forming minerals. India is probably the biggest supplier of mica.
Natural mica contains many other materials including, iron, sodium, ferric oxide, and lithium.
Because of the variability in composition of natural mica, mica destined for use in capacitors must be carefully inspected and classified, which adds to the manufacturing cost. All varieties of mica are chemically very stable and inert. Mica s thermal, electrical, and chemical properties make for excellent capacitors. This, combined with low inductance designs, result in capacitors that are ideal for high frequency and RF applications. Specification sheets of mica capacitors commonly show parameters plotted into the gagahertz range.