What metamorphic rock that has regional metamorphism has the highest grade of metamorphism?  GneissPhyllite

The metamorphic rock that has the highest grade of metamorphism within the context of regional metamorphism is Gneiss.

Explanation:

1. Metamorphic Grades: Metamorphism occurs at various grades, which refers to the intensity and conditions under which the rock undergoes transformation. The grades are usually categorized into low, medium, and high.

2. Types of Metamorphic Rocks:

   • Phyllite represents a lower grade of metamorphism, typically characterized by a shiny appearance and a foliation due to very fine-grained minerals.
   • Gneiss, on the other hand, represents a higher grade of metamorphism. It is typically banded and coarse-grained, with a distinct foliation formed under high temperature and pressure conditions.

3. Regional Metamorphism: This process affects large areas of the Earth's crust and is usually associated with tectonic plate movements, leading to high pressures and temperatures, which result in the formation of higher-grade metamorphic rocks such as gneiss.

In summary, gneiss is the metamorphic rock with the highest grade of metamorphism formed through regional metamorphic processes, while phyllite represents a lower grade.