Difference Between Igneous, Sedimentary, and Metamorphic Rocks (with Table)

The difference between igneous, sedimentary, and metamorphic rocks lies in their origin, formation, texture, classification, and so on.

Igneous rocks are derived from magma (molten rocks) or lava (molten rocks that break through the earth’s surface) that cool down and solidify. These rocks are mainly crystalline. Some examples of igneous rocks include granite, basalt, and pumice.

Sedimentary rocks are derived from the accumulation and deposition of other pre-existing rocks or tiny pieces of animal remains that get cemented at the bottom of water bodies.  These rocks are fragmentary in structure. Examples of sedimentary rocks include sandstone, chalk, and coal.

Metamorphic rocks are formed when pre-existing rocks undergo chemical and solid-state changes due to heat and pressure. These rocks are very hard and may appear to be foliated. Some examples of metamorphic rocks include marble, quartzite, phyllite, etc.

Comparison Table Between Igneous, Sedimentary, and Metamorphic Rocks

Parameters of ComparisonIgneous RocksSedimentary RocksMetamorphic Rocks
OriginIgneous rocks are derived from molten material (magma or lava).Sedimentary rocks are derived from sediments of pre-existing rocks, fossils, and tiny pieces of animal remains.Metamorphic rocks are derived from other rocks.
FormationIgneous rocks are formed when molten material from volcanoes cools down and solidifies.Sedimentary rocks are formed when sediments are accumulated, deposited, and cemented at the bottom of water bodies.Metamorphic rocks are formed when other pre-existing rocks go through chemical and physical changes due to heat and pressure.
StructureIgneous rocks mainly have a crystal-like structure.Sedimentary rocks have a fragmentary structure and contain an inner layering called bedding.Metamorphic rocks are very hard and may appear to be banded or layered.
TextureThe texture of igneous rocks depends on how fast it has cooled down. Textures range from coarse-grained to glassy.The texture of sedimentary rocks depends on their clast, age, and depositional setting. These are generally grainy.The texture of metamorphic rocks is foliated due to pressure. Some rocks may even appear to be non-foliated and banded.
TypesIgneous rocks are of two types – intrusive (solidified from magma below the earth’s surface) and extrusive (solidified from lava on the surface of the earth)Sedimentary rocks are of three types – clastic sedimentary rocks (detrital), organic sedimentary rocks (biochemical), and chemically precipitated sedimentary rocks.Metamorphic rocks can be divided into two basic categories – foliated metamorphic rocks and non-foliated metamorphic rocks.
ExamplesIntrusive igneous rocks include – granite, diorite, pegmatite; Extrusive igneous rocks include – basalt, tuff, pumice, scoria, etc.Limestone, iron ore, chalk, coal, sandstone, siltstone, shale, flint, etc.Slate, marble, quartzite, phyllite, gneiss, hornfels, etc.

What are Igneous Rocks?

Igneous rocks are formed when molten material cools down and solidifies to form crystalline material. Since these rocks are derived from liquid form (as opposed to sedimentary and metamorphic rocks which are derived from pre-existing rocks), they can be called ‘primary’ rocks.

Igneous rocks are abundant as they make up 95 percent of the upper section of the earth’s crust. Moreover, there are around 700 different varieties of these rocks. Out of these, granite is a widely known igneous rock that is used for constructing most kitchen surfaces.

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What are Sedimentary Rocks?

Sedimentary rocks are derived from pre-existing rocks and pieces of once-living animals that go through the process of weathering, transport, deposition, compaction, and cementation. These rocks are formed over millions of years at the bottom of water bodies like oceans and rivers.

Sedimentary rocks can be categorized into clastic, organic, and chemically precipitated rocks. Clastic sedimentary rocks are those which are created in response to mechanical weathering on pre-existing rocks.

Organic sedimentary rocks are those which are derived from accumulated and deposited remains of dead plants and animals. Sometimes, a chemical reaction between two minerals present in rocks may occur. On cooling down, these minerals precipitate and turn into chemical sedimentary rocks.

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What are Metamorphic Rocks?

Metamorphic rocks are formed when pre-existing rocks are subjected to change in heat and pressure causing physical and chemical changes in them. The rocks go through a temperature of above 150 degrees Celsius and pressure of around 1500 bars to form new rocks.

Metamorphic rocks can be categorised into two types – foliated and non-foliated rocks. Foliated rocks are those which have a structure of thin layers, while non-foliated rocks have no such structure.

Metamorphic rocks constitute most of the earth’s crust. It is a rock found in abundance. Interestingly, since the Taj Mahal is made up entirely of marble, the monument is one big metamorphic rock.

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Main Differences Between Igneous, Sedimentary, and Metamorphic Rocks

  1. Igneous rocks are formed from molten material that solidifies. On the contrary, sedimentary and metamorphic rocks are derived from pre-existing rocks.
  2. Igneous rocks are crystalline in structure, sedimentary rocks tend to be fragmentary and stratified whereas metamorphic rocks are either foliated or non-foliated.
  3. 95 percent of the upper section of the earth’s crust is made from igneous rocks, while the latter constitute the remaining percentage among other rocks and minerals.
  4. Metamorphic rocks are found closer to the earth’s surface as compared to igneous rocks which are found in the earth’s crust or mantle and sedimentary rocks that are found at the bottom of water bodies.
  5. The most widely known igneous rock, granite, is used for constructing kitchen surfaces. Rock salt is a sedimentary rock that is consumed across the world. Metamorphic rocks such as marble are used to construct homes and buildings.

Conclusion

Igneous, sedimentary, and metamorphic rocks can be told apart easily by their formation, texture, structure, and so on. The three types of rocks may sometimes be the same mineral or sediment going through a rock cycle.

For example, an igneous rock may go through the process of weathering and cementation to form a sedimentary rock. This rock may further change into a metamorphic rock if subjected to changes in heat and pressure.

References

  1. https://www.sciencedirect.com/science/article/pii/0016714285900018
  2. https://pubs.geoscienceworld.org/gsa/gsabulletin/article/86/8/1085/201860