Metamorphic rocks forms due to heat and temperature which changes the original rock or parent rock into new rock. The parent rocks are sedimentary, igneous, or metamorphic. The metamorphic word comes from Greek and means “to change form“.
Metamorphic rocks are forms due to changes through a geological process like tectonic movements and magma intrusions. These geological process changes the mineral composition and texture of the pre-existing igneous and sedimentary rocks to form metamorphic rocks. The process through which existing rocks change into metamorphic rocks is called metamorphism. Metamorphic rocks form 12% of the earth’s surface. The study of metamorphic rocks gives us information about the temperature and pressure that occur at great depth within the earth’s crust.
There are 3 factors that cause an increase in pressure and the formation of metamorphic rock.
- Weight of the overlying layer of sediment.
- Stress due to plates colliding.
- Stress due to plates sliding past each other.
Table of Contents
Types of Metamorphism
There are 3 types of metamorphism are contact, regional, and dynamic metamorphism.
- Contact Metamorphism
- Regional Metamorphism
- Dynamic Metamorphism
Contact Metamorphism:
When magma comes in contact with rocks(country rock), the temperature is highest near magma and decreases to distance. the area near the magma alters the rocks, the area surrounding the igneous intrusion is called contact metamorphism.
Regional Metamorphism:
Happened in a greater area. large geological process e.g mountain building produces regional metamorphism. schist and gneiss produce due to metamorphism.
Dynamic Metamorphism:
It also produces by mountain building. rock bend, folded, crushed, and sheared because of heat and pressure. breccias composed of angular shattered rock fragments to very fine-grained, granulated, or powdered rocks with clear foliation and lineation. direct pressure is the main agent of dynamic metamorphism.
Metamorphic Rocks and Their Parent Rocks
There are two types of Metamorphic Rocks
- Foliated Metamorphic Rocks
- Non-Foliated Metamorphic Rocks
Foliated Metamorphic Rocks
Foliated metamorphic rocks are formed due to direct exposure to pressure and heat. Most important and largest groupings of metamorphic rocks. Foliated metamorphic rocks have four distinguishable types of aligned textures and normally have a banded or layered appearance. Examples are slate, gneiss, phyllite, and schist.
| Metamorphic Rocks | Parent Rocks | Mineralogy | Metamorphism | Crystal Size |
|---|---|---|---|---|
| Slate | Shale | Clay mineral | low-grade Regional Metamorphism | Very Fine |
| Phylite | Shale | Clay mineral, Muscovite, Biotite | low-grade Regional Metamorphism | Fine |
| Schist | Shale, Basalt | Muscovite, Quartz, Garnet, Biotite, Plagioclase | Medium-grade Regional Metamorphism | Medium to Course |
| Gneiss | Basalt, granite, shale | plagioclase, orthoclase, quartz, biotite, amphibole, pyroxene | high-grade regional metamorphism | Medium to Course |
| Serpentinite | Peridot, dunite | serpentine, magnetite, talc, chlorite | Low-grade regional metamorphism | Medium to Course |
| Blue schist | Basalt | Blue amphibole, Green mica | low-grade Regional Metamorphism, High pressure | Fine to Medium |
| Green schist | Basalt | Green Amphibole, Green mica, Plagioclase | Medium-grade Regional Metamorphism | Fine to Medium |
| Amphibolite | Basalt | Amphibole, Plagioclase, Biotite, Quartz | Medium-grade Regional metamorphism | Medium to Course |
Non-Foliated Metamorphic Rocks
Non-foliated metamorphic rocks are formed due to tectonic movement or direct pressure and Its formation is dependent on existing rocks. These metamorphic rocks don’t have bands or layered appearance. Examples are quartzite, hornfels, and novaculite.
| Metamorphic Rocks | Parent Rocks | Mineralogy | Metamorphism | Crystal Size |
|---|---|---|---|---|
| Quartzite | Sandstone | Quartz | Regional or Contact Metamorphism | Fine to course |
| Marble | Limestone | Calcite | Regional or Contact Metamorphism | Fine to course |
| Hornfels | Shale | Pyroxene, Amphibole, Plagioclase | Contact Metamorphism | Fine |