They are classified on the basis of texture (foliated vs. Non-foliated), grain-size, and mineral composition. Texture: metamorphic rocks may have either foliated (layered) or non-foliated texture.
On What Basis Can Metamorphic Rocks Be Identified?
Metamorphic rocks are rocks that have been changed by heat, pressure, or chemical processes. The original rock may be igneous, sedimentary, or even another metamorphic rock.
Metamorphic rocks are often named for the type of rock from which they came (such as shale becoming slate) or for the type of change that took place (such as sandstone becoming quartzite).
There are two main types of metamorphism: contact metamorphism and regional metamorphism. Contact metamorphism happens when hot magma comes into contact with cooler rock.
The rock closest to the magma is changed the most. Regional metamorphism happens when rocks are buried deep underground and are changed by the heat and pressure of the surrounding rock.
There are three main ways to identify metamorphic rocks: texture, mineralogy, and structure. Texture is the size, shape, and arrangement of the grains in a rock.
Metamorphic rocks can have different textures depending on the type of rock they started as and the type of metamorphism that occurred.
For example, a sedimentary rock with large, well–rounded grains can become a metamorphic rock with small, angular grains. Mineralogy is the