片麻岩, or "gneiss," is a type of metamorphic rock characterized by its banded appearance and coarse-grained texture. It forms from the alteration of pre-existing rocks, such as granite or sedimentary rocks, under high temperature and pressure conditions. The mineral composition typically includes quartz, feldspar, and mica, which contribute to its distinctive layering. This rock is commonly found in regions that have experienced significant geological activity, such as mountain ranges. Gneiss is often used in construction and decorative stonework due to its durability and aesthetic appeal. Its formation process is a key aspect of the rock cycle, illustrating the dynamic nature of Earth's geology.