What is Metamorphic Rock, Formation Process, and Examples

The existence of various kinds of rocks that are around us does have benefits for human life itself. Without realizing it, we need the presence of these stones. We can use the presence of these stones to make building materials which will be very useful to us later. There are also those that are used directly as building materials or just for aesthetics. In ancient times, these rocks were actually widely used by humans.

Not only useful for building materials, the stones around us can also provide aesthetic value or beauty. The stone is generally used to decorate the house or garden. These types of rocks are also used as part of the interior design of a building.

In fact, there are many kinds of rocks. One of them is metamorphic rock. The term metamorphic is one of the names of the types of rocks that complement igneous rocks and also sedimentary rocks. This metamorphic rock is a type of rock that changes shape. Where this rock is the result of the transformation of the previous rock type into a rock that complements igneous and sedimentary rocks.

Rock itself is a solid object made naturally from mineraloids or minerals, which can be found on the surface of the earth wherever these objects are located. Therefore, in this article we will discuss more deeply about metamorphic rocks and their various forms.

What Is Metamorphic Rock?

Understanding or definition of metamorphic rock is often associated as metamorphic rock. This is because this metamorphic language is more towards a foreign language, while the metamorphic language looks more like Indonesian. This metamorphic rock is a group of rocks that have undergone a transformation or change in shape due to the lifting or erosion of the soil, then transformed into new rocks.

Soil erosion that lifts rocks into metamorphic rocks requires high temperatures and pressures. Therefore, we often encounter these metamorphic rocks in volcanic soils around volcanoes. Where rocks that are eroded by low temperatures do not turn these rocks into metamorphic rocks, but become sedimentary rocks.

Broadly speaking, metamorphic rock is a class that results from changes in existing rock in response to changes in environmental conditions, such as variations in temperature, pressure, and also mechanical stress and the addition or reduction of chemical components. The existing rock may be sedimentary, igneous, or other metamorphic rock.

Definition of Metamorphic Rocks According to Experts

Here are some definitions of metamorphic rocks according to experts, including:

1. American Geosciences Institute

According to him, metamorphic rocks are rocks that have been changed by intense heat or pressure when they were formed. Under conditions that are sufficiently hot and depressed deep in the earth’s crust, either sedimentary or igneous rocks can be converted into metamorphic rocks. One way to think about the process of metamorphism or metamorphism is to consider what happens when soft earthen objects are placed in a furnace and then heated to very high temperatures. Then the ground will change from being slippery to hard. The object cannot be changed back to its original form, because the material itself has changed. That’s what happens on a large scale underground to produce metamorphic rocks.

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The Process of Occurrence of Metamorphic Rocks

As previously explained, this metamorphic rock will only form when a special metamorphic process occurs on the earth’s surface. These rocks will not form directly, but must go through this process of metamorphism. Where the process will change the parent rock in the form of igneous rock or sedimentary rock into metamorphic rock with different shapes and characteristics and colors compared to the original rock. In general, the process of forming metamorphic rocks can be simplified into several stages, namely:

a. Available main rock or protolith
b. Protolith has been exposed to the process of metamorphism
c. The protolith rock begins to change its characteristics
d. Formation of metamorphic rock

Initially, all metamorphic rocks originate from a parent rock known as a protolith. Where these rocks are then exposed to metamorphic processes which are influenced by high pressure and high temperatures as well. This metamorphism process will slowly change the characteristics of the protolith rock into another rock that is metamorphic. At the end of the long process of metamorphism, this protolith rock will turn into a complete metamorphic rock that already has certain characteristics and forms of foliation. In that section, we will learn about the factors that influence the process of metamorphism and also the type of metamorphism that occurs in the formation of these rocks.

Examples of Metamorphic Rocks

The following are some examples of metamorphic rocks that need to be understood, including:

1. Slate Metamorphic Rock

This slate rock is a metamorphic rock in which the process of formation is from the transition process of Shale or Mudstone sedimentary rock or claystone at very low pressure and temperature. Where this slate metamorphic rock has a foliated structure consisting of various types of very fine grains. Slate rock itself was previously a type of shale and mudstone rock. The colors of this slate rock are black, gray, brown, red, yellowish, and others. Meanwhile, the grain texture of this slate rock has very fine grain. This slate rock can easily split into very thin sheets. The function of the thin-shaped slate is usually used for slate, while the thicker ones are used for sidewalks and roofs.

2. Philite Metamorphic Rock

This phyllite rock is a type of metamorphic rock which usually consists of quartz, sericite mica, and also chlorite. Where this phyllite rock comes from the continuation of the transition process from slate rock. Because, the origin of phyllite rocks comes from slate rocks, therefore the main material for the formation of phyllite rocks is shale rock. The colors of phyllite are silver, red, white, purple, brown and greenish. The grain size of phyllite tends to be smoother than slate. So when viewed directly, the stone is very neat.

Meanwhile, the structure of this phyllite rock is foliated. The composition of the material itself is made of mica and quartz. The temperature and pressure during the formation of phyllite rocks are from low to medium. This phyllite rock has characteristics that divide following the wave surface. Where phyllite rock is useful as an insulator or a good conductor of electricity. In addition, this type of stone can also be used as an additional material for building construction, floors, roofs, and others.

3. Gneiss Metamorphic Rock

Gneiss rocks are rocks that originate or metamorphose from an igneous rock that exists at high temperatures and pressures. Usually, these gneiss rocks have colors such as black, gray, brownish, silver, blue, greenish, and also yellowish. The grain size of this gneiss stone tends to be medium and has a foliated structure. While the composition in this gneiss rock is quartz and feldspar. The most prominent characteristics of this gneiss rock are quartz and feldspar which are seen alternating with layers similar to mica. Generally, this gneiss rock is widely used as a building material.

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4. Schist Metamorphic Rock

Schist is a metamorphic rock derived from basalt. Generally, these schist rocks are black, purplish, greenish, brownish, golden, yellowish, and reddish in color. For the grain size of medium or medium sized schist rocks. The composition contained in this schist rock is mica and granite. Meanwhile, the structure of the schist itself is foliated. The temperature and pressure during the process of forming schist rocks is very high. Therefore, schist rocks have wavy characteristics and sometimes garnet crystals are present in them. For its own use, usually this type of rock is used as a building construction material.

5. Marble Metamorphic Rock

Marble rock is formed from the metamorphism of limestone which gets pressure and also high hot temperatures. So that it changes shape and also crystallizes calcite. The main ingredient of this marble rock is calcium carbonate. Marble rocks usually have a light yellowish brown color. As for its nature, marble rock has solid, compact, and non-foliated properties. Marble rock is one of the materials for buildings, floors, walls, and is also sometimes used as a craft material.

6. Quartzite Metamorphic Rock

Quartzite rock is one part of the metamorphic rock that has a strong texture. Where this rock is formed when sandstone gets hot pressure and high temperatures. Quartzite rocks have colors that are yellowish gray, red, and brown. For the stone structure itself, namely nonfoliation. While the composition of quartzite as a whole consists of quartz rocks. The main function of this quartzite rock is as the main ingredient for the glass and ceramic industry which can be used as household furniture.

7. Millonite Metamorphic Rock

Milonite rock is a metamorphic rock that contains a lot of compact minerals. Where this milonite rock crystallizes dynamically following the mineral carrier substance that forms metamorphic rocks. The colors of these rocks are gray, brown, black, and also slightly bluish. This milonite rock has a structure that is not foliated. What is unique about this milonite rock is that its composition varies for each rock. Generally, milonite rocks are formed at high temperatures and pressures. In addition, what is interesting about milonite rocks is that a function has not been found for the utilization of these rocks.

8. Filonite Metamorphic Rock

Filonite rock is a metamorphic rock that forms at higher temperatures and pressures than slate. So, this phylonite rock is formed from the metamorphism of shale rocks and mudstones. This phylonite rock has little resemblance to milonite, it’s just that the difference is in the grain of the rock. Where the grains of phylonite rock are coarser than milonite rocks. The color characteristics of this phylonite rock are gray, greenish, bluish, preferring silver, brownish, and also blackish. This rock has a structure that is not foliated. While the composition of this phylonite rock is quartz and mica.

The characteristic of phylonite rock is that it has a surface that looks shiny. The function of this rock is to be used as the main material for making statues and also decoration because it has good characteristics to use it.

This is an explanation of various examples of metamorphic rocks and their characteristics. Hopefully useful.