Here's why:
* Slate: Slate is formed from low-grade metamorphism of shale. Mica, specifically muscovite, is a common mineral found in shale and persists in the metamorphic process.
* Schist: Schist forms from a higher grade of metamorphism than slate. The heat and pressure cause the mica crystals to become larger and aligned, giving schist its characteristic foliation.
* Gneiss: Gneiss is formed from high-grade metamorphism. Mica, along with other minerals like quartz and feldspar, become segregated into bands, giving gneiss its distinctive banding.
While mica is common to all three rocks, the specific type of mica can vary depending on the original rock and the degree of metamorphism.
