Here's the breakdown:
* Starting Point: Gneiss can originate from both igneous and sedimentary rocks.
* Igneous: Think granite, gabbro, or basalt.
* Sedimentary: Think sandstone, shale, or limestone.
* Transformation: These original rocks are subjected to high temperatures and pressures deep within the Earth's crust. This process causes:
* Recrystallization: Minerals within the original rock change their size and orientation.
* Banding: Minerals separate into distinct layers or bands, giving gneiss its characteristic striped appearance.
Key point: Gneiss is a high-grade metamorphic rock, meaning it has undergone significant transformation.
