For 10 points, name this kind of mineral known for its ability to easily fragment into sheets and flakes.
Phyllite is a type of schist that contains very small grains of this mineral. Along with quartz and feldspar, this type of mineral is commonly found in pegmatites, where tourmaline content is a good indicator of a high content of this mineral. The end window of a GeigerMüller tube is often made of this mineral. Bunsen and Kirchoff discovered rubidium in lepidolite, a type of this silicate mineral, which along with talc and graphite exhibits perfect basal cleavage. Examples of this mineral include glauconite, biotite, and muscovite. For 10 points, name this kind of mineral known for its ability to easily fragment into sheets and flakes.
Phyllite is a type of schist that contains very small grains of this mineral.
mica