1. Muscovite mica- KAl2(AlSi3O10)(OH)2 - has greater dielectric strength than any other insulating material. It surpasses all mica in dielectric strength, thermal endurance, mechanical strength, moisture resistance, transparency, flexibility, resilience, toughness and perfection of cleavage and is therefore recognized as the best Mica for electrical and electronics devices. It is almost insensitive to atmospheric weathering and offers greater resistance to outside chemical influence. Muscovite Mica is harder than Phlogopite Mica.
Muscovite Mica is the most commonly used Mica in electrical insulation and since it has the best electrical properties of all Mica. High quality Mica cleaves the easiest and into the thinnest sheets and with the fewest imperfections that could be seen at the atomic or near atomic scale with AFM or TEM instrumentation. Muscovite Mica is commonly divided into two color groups:
Ruby : varies in color from clear to pink to red / brown
Green: varies in color from pale green to olive to dark green
Ruby Muscovite : Color ranges from an almost white through pink to a light ruby and into shades of brownish ruby and brown. Ruby Mica has excellent cleavage capabilities permitting it to be split into the thinnest desired film without the risk of cracking.
Green Muscovite : Ranges from light to pale green through yellowish and olive green to a dark green. Color as such has less significant influence on quality. Still ruby Muscovite is generally preferred especially in the higher qualities as it is considered to be superior to green Mica for applications requiring high dielectric strength and low power loss (or high Q). Ruby and green Mica have excellent cleavage permitting it to be split into the thinnest desired film without the risk of cracking. Use of ruby and green Mica is a matter of preference and application.
2. Phologopite Mica - KMg3(AlSi3O10)(OH)2 - is a hydrous potassium magnesium aluminium silicate. Here the calcination temperature is reached at about 800 C. Generally speaking, Phlogopite Mica is softer than Muscovite mica and this for instance makes it more suitable for the manufacture of commutator micanite used in commutators of flush running designs.
Phlogopite Mica is commonly called amber mica and varies in color from light silver to dark brown. Phlogopite Mica has poor electrical properties and chemical resistance in comparision to Muscovite mica