Metamorphism is a geological process involving rocks changing their form. The process requires millions of years in transformation. Earlier, the transformed rocks could either have been igneous, sedimentary, or even older metamorphic rocks. The heat and pressure of the Earth's crust bring about profound changes in terms of physical as well as chemical properties, and give new textures to the rock. The new texture that develops is through the process of recrystallization. The texture and the kinds of minerals they consist of are how these rocks are classified. Here, we will have a look at some related facts, and also the various types of metamorphic rocks.

• Metamorphic rocks can be divided on the basis of their metamorphism - regional, thermal, hydrothermal, and fault zone metamorphism.
• Regional metamorphic rocks are found in the mountainous regions, and are developed in accordance to the pressure exerted onto them by the Earth's crust. This phenomenon affects a very large area. The transformation is also affected by the thermal intensity. More pressure leads to major changes in the texture of the rock.
• On the other hand, thermal metamorphic rocks are formed as a result of high thermal intensity of the magma and Earth's pressure. The more the heat, the more changes will occur to the rocks.
• Hydrothermal metamorphic rocks are formed when hot fluids from hot springs circulate between the rocks.
• Fault zone metamorphic rocks are formed as a consequence of changes that happens along fault lines within the Earth's crust.
• Most classifications of metamorphic rocks involve first separating the rocks into two categories by their texture -foliated rocks and non-foliated rocks.
• The foliation or layering that occurs in these rocks is because of the immense directional pressure they undergo deep within the Earth, usually along the boundary of a converging tectonic plate. In this environment, over an enormous time period, flat crystals of minerals as well as fragments, like stream pebbles and volcanic pyroclasts, progressively become perpendicular to the direction of the pressure. Apart from the effects of the pressure, the increase of the temperature can also result in minerals such as chlorite and mica re-crystallizing into bigger crystals that are more visible. These rocks are termed as foliated rocks.
• The rocks which do not have planar patterns of strain or stretching are termed as non-foliated metamorphic rocks. These rocks are most often deduced from single mineral sedimentary rocks.
• High temperature and pressure erases out the fossils of the metamorphic rocks.
• Metamorphic rocks do not have pores or openings, and may be accompanied with visible layers of crystals.

Amphibolite Parent Rock: Basalt The rock consists of amphiboles, is generally dark-colored and heavy, with a weakly foliated structure. It is used for used for construction purposes, building facings and paving. It is easily available and has attractive textures. Blueschist Parent Rock: Basalt This rock derives its name from its color. The metamorphism is generally accompanied by high pressure and low temperature. The presence of the mineral glaucophane imparts blue color to this rock. Marble Parent Rock: Limestone or dolomite Both dolomite and limestone contain calcium carbonate in large concentrations. Compared to its parent rock, marble is much harder. This enables it to get polished, and makes it popular as a building material. It is also used in bathtubs, floor tiling, sink tops, kitchen countertops, and so on. Artists do use it as a carving material. Marble is made up of various sized crystals, and also has many variances in color because of the impurities that are present during the formation process. Hence, marble can be white, gray, black, red, green, pink, banded and mottled. Eclogite Parent Rock: Peridotite This rock is formed under great pressure and temperatures. It consists of pyroxene and red garnet, along with small amounts of stable minerals. The color of eclogite is red-green, which makes it quite beautiful to look at. Being a dense rock, eclogite helps in convection within the Earth's crust. Greenschist Parent Rock: Basalt This rock is formed under low temperatures and pressure. The rock gets its color from the presence of chlorite, epidote, or actinolite. Slate Parent Rock: Shale The rock is fine-grained, containing perfect cleavage, which enables splitting it into fine sheets. Slate generally contains dark- to light-brown streaks. It is formed because of comparative low pressures and temperatures, and is referred to as low-grade metamorphism. It has been used in various ways over the years; for example, as grave markers or headstones. However, one of the problems with slate is the perfect cleavage it has, which resulted in gravestones splitting and cracking along the cleavage lines. It is also commonly used for chalkboards. Nowadays, due to its cracking and splitting, and its weight, slate is not used much. Schist Parent Rock: Shale This metamorphic rock is classified as medium grade, which means it has been formed by more pressure and heat compared to slate. This rock is coarse-grained, with the individual grains of the minerals that it is made up of being visible to the naked eye. Most of the original minerals are transformed into flakes, and since it has experienced far more pressure, it is usually found crumpled or folded. Usually, schists are named according to the main mineral they have been formed from. For example, talc schist, garnet mica schist, hornblende schist, and biotite mica schist. Gneiss Parent Rock: Granite or shale This rock is classified as high grade, which means that compared to schist, it has been subjected to more pressure and heat. Gneiss is distinctly banded and is coarser than schist. The banding comprises alternating layers, which are made up of different minerals. One of the most important minerals that gneiss is made up of is feldspar, along with quartz and mica. Gneiss can also form from the metamorphosis of sedimentary rocks like shale or sandstone, or from igneous rocks like granite. Gneiss is used as a building stone and for paving. Hornfel Parent Rock: Basalt, limestone and shale This rock does not appear in crystalline form, but the small grains enclosed fit in as a mosaic. Hornfel is non-foliated and its texture is banded. Its color is variable and largely depends on the source of rock it has metamorphosed from. Quartzite Parent Rock: Quartz sandstone When sandstone is metamorphosed it turns into quartzite. It becomes more harder than its parent rock. It is formed when sandstone comes into contact with magma that is deeply buried. Quartzite appears quite similar to sandstone, and the best way to tell the difference is to break both the rocks. While sandstone shatters into many grains, quartzite breaks across the grains. Serpentinite Parent Rock: Peridotite This rock is mainly composed of serpentine minerals - antigorite, lizardite and chrysotile. The color can be green to dark-green or reddish-brown to black. It is very finely grained, and its texture is variable. It is used as a decorative stone in architecture. It was used to make chimneys earlier, due to its heat-resisting property. Soapstone Parent Rock: Peridotite This rock is primarily composed of talc and contains small amount of chlorite, mica and amphiboles. It is formed when the Earth's crust is subjected to high heat and pressure. Soapstone is used for countertops in kitchens, making bowls and plates, electrical panels, and also as wall tiles and floor tiles. Phyllite Parent Rock: Shale or pelite Shale being the parent rock, is metamorphosed to become a fine grained phyllite, consisting of clay minerals. This rock is subjected to a greater degree of heat and pressure than slate, and also has larger crystals. The chief composition of phyllite consists of quartz, sericite mica, and chlorite.