MICA
Garnet Mica Schist from Belgium (I think)
Schist: A medium- or coarse-grained metamorphic rock with a large proportion of platy minerals, such as mica, which are aligned in one direction, defining an often undulating foliation. Fairly high temperatures (>400C) and pressures are required for its formation.
So there you go!! Biotite is a type of mica too.
Forms in conditions of medium-grade, regional metamorphism, at deeper levels than phyllite. The pressure is moderately high, and temperature has been influential in changing the rock's original character.
Mica: A type of sheet silicate mineral (biotite: brown - muscovite: white)
Garnet: A silicate mineral found in metamorphic rocks. Various chemical compositions are possible.
The general formula for mica is AB2-3 (Al, Si)Si3 O10 (F, OH)2. In most micas the A is usually potassium, K, but can be calcium, Ca, or sodium, Na, or barium, Ba, or some other elements in the rarer micas. The B in most micas can be aluminum, Al, and/or lithium, Li, and/or iron, Fe, and/or magnesium, Mg. The mica group is a large group with nearly 30 members recognized, but only a few are common. Those few however make up a large percentage of the most common rock types found in the Earth's crust.
mica nero (black) from Vesuvius