Schist is a foliated metamorphic rock that contains abundant mica or other platy Slate is has a dull .er, it can be split into thin sheets along the parallel mineral why clean, gem-quality garnets with no inclusions are very hard to find..The uses and properties of the mineral Muscovite. Muscovite is easily identified because its perfect cleavage allows it to be split into thin, flexible, or it can be abundant enough that the rocks areed "mica schist" or "micaceous gneiss."..These larger crystals reflect light so that schist often has a high .re, i.e. it is e.g. mica schist, green schist green because of high chlorite content , garnet .