The extent to which orthoclase feldspar is absent in acid pegmatites is typical of an abundance of mica in a mineral lode. Another indication of significant deposits of mica is the high occurrence of tourmaline and degraded feldspar in pegmatites. Some of the common forms of mica include muscovite, phlogopite, biotite, lepidolite and paragonite.
Muscovite is formed by layers. Muscovite is so delicate when you hold it, it can break. One layer, then another, it keeps building but never grows humongous because people find it and use it.