Igneous rocks are derived from magma (molten rocks) or lava (molten rocks that break through the earth’s surface) that cool down and solidify.
Sedimentary rocks are derived from accumulating and depositing other pre-existing rocks, or tiny pieces of animal remains that get cemented at the bottom of water bodies.
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.
Key Takeaways
- Igneous rocks are formed from cooled magma or lava and include basalt and granite; sedimentary rocks are formed from the accumulation and compaction of sediment, such as sandstone and limestone; metamorphic rocks are formed from the transformation of existing rocks due to heat and pressure, such as marble and quartzite.
- Igneous rocks have a crystalline structure and can be extrusive (formed from lava) or intrusive (formed from magma); sedimentary rocks are layered and contain fossils or other evidence of past environments; metamorphic rocks may have a banded or foliated appearance due to the compression and recrystallization of minerals.
- Igneous and metamorphic rocks are harder and more resistant to weathering than sedimentary rocks; sedimentary rocks are more likely to contain fossils and provide evidence of past environments.
Igneous Sedimentary vs. Metamorphic Rocks
Magma cooled down to form crystal-like solids with glassy surfaces known as igneous rocks. Sedimentary rocks are made from long-existing rocks; animal remains become hardened after deep water. Metamorphic rocks are made from old rocks that undergo physical or chemical changes.
Comparison Table
| Parameters of Comparison | Igneous Rocks | Sedimentary Rocks | Metamorphic Rocks |
|---|---|---|---|
| Origin | Igneous 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. |
| Formation | Igneous 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 undergo chemical and physical changes due to heat and pressure. |
| Structure | Igneous 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. |
| Texture | The 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 class, age, and depositional setting. These are grainy. | The texture of metamorphic rocks is foliated due to pressure. Some rocks may even appear to be non-foliated and banded. |
| Types | Igneous 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. |
| Examples | Intrusive igneous rocks include – granite, diorite, and 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, they can be called ‘primary’ rocks.
Moreover, there are around 700 different varieties of these rocks. Out of these, granite is a widely known igneous rock used to construct most kitchen surfaces.
What are Sedimentary Rocks?
Sedimentary rocks are derived from pre-existing rocks and pieces of once-living animals undergoing 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.
Sometimes, a chemical reaction between two minerals present in rocks may occur. On cooling down, these minerals precipitate and turn into chemical sedimentary rocks.
What are Metamorphic Rocks?
Metamorphic rocks are formed when pre-existing rocks are subjected to changes in heat and pressure, causing physical and chemical changes. 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 categorized into two types – foliated and non-foliated rocks.
Metamorphic rocks constitute most of the earth’s crust. It is a rock found in abundance.
Main Differences Between Igneous, Sedimentary, and Metamorphic Rocks
- Igneous rocks are formed from molten material that solidifies. On the contrary, sedimentary and metamorphic rocks are derived from pre-existing rocks.
- Igneous rocks are crystalline in structure; sedimentary rocks tend to be fragmentary and stratified, whereas metamorphic rocks are either foliated or non-foliated.
- https://www.sciencedirect.com/science/article/pii/0016714285900018
- https://pubs.geoscienceworld.org/gsa/gsabulletin/article/86/8/1085/201860
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