Metamorphic rocks are classified based on their texture, mineralogy, and composition. The facies classification of metamorphic rocks is based on the conditions of temperature and pressure under which the rock formed. The following are the facies classification of metamorphic rocks:
- Zeolite facies: This facies forms at low temperatures (less than 200°C) and low pressure. The minerals that typically form in this facies are zeolites, chlorite, and prehnite.
- Greenschist facies: This facies forms at low to medium temperatures (between 200°C and 500°C) and low to medium pressures. The minerals that typically form in this facies are chlorite, amphiboles, and plagioclase.
- Amphibolite facies: This facies forms at medium to high temperatures (between 500°C and 800°C) and medium to high pressures. The minerals that typically form in this facies are amphiboles, plagioclase, and garnet.
- Granulite facies: This facies forms at high temperatures (above 800°C) and high pressures. The minerals that typically form in this facies are feldspars, pyroxenes, and garnet.
- Eclogite facies: This facies forms at high pressures (greater than 1.2 GPa) and relatively low temperatures (less than 800°C). The minerals that typically form in this facies are garnet and omphacite.
Each of these facies reflects a specific range of conditions under which the metamorphic rocks formed, and the facies classification helps geologists to better understand the geological history of the rocks
