Here's why:
* Mica's Structure: Mica minerals, such as biotite and muscovite, have a layered, sheet-like structure. This structure allows them to align themselves parallel to each other under pressure.
* Foliation Formation: When rocks are subjected to intense pressure during metamorphism, the mica crystals arrange themselves perpendicular to the pressure direction. This creates distinct layers or bands of aligned mica, which is the defining feature of foliation.
While other minerals can be present in schists, mica is the primary mineral responsible for the strong, visible foliation that characterizes this metamorphic rock.
