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Types of rocks: igneous, sedimentary and metamorphic (with examples)

There are three types of rocks: igneous, sedimentary and metamorphic. Rocks are a conglomerate of various types of minerals or other materials.

Rock types are determined by the processes involved in their formation. On the other hand, a rock can give rise to another type of rock, in what is known as the rock cycle.

definition Rock resulting from the solidification of molten rock Rock resulting from the compaction of sediments Rock resulting from the transformation of other rocks
Processes involved in training Fusion and solidification Compaction and cementation Pressure and temperature
type intrusive
By chemical precipitation
Not foliated
examples Slag, pumice, obsidian, basalt, porphyry, granite, andesite, gabbro, granite. Sandstone, halite, coal, limestone, lutolite, travertine, gypsum. Green schist, serpentine, marble, gneiss, quartzite, epidosite.

types of rocks: igneous, sedimentary and metamorphic

igneous rocks

Igneous rocks are rocks that form when molten material in the Earth’s crust cools. The magma is the molten material below the earth’s surface and the lava is the molten material that flows to the surface.

There are two types of igneous rocks:

  • Extrusive igneous rock: also called volcanic rock, it is the rock that forms when lava hardens. Examples of extrusive stones are obsidian and rhyolite.
  • Intrusive igneous rock: also called plutonic rock, when magma changes from fluid to solid underground. Examples of intrusive stones are basalt and granite

The chemical composition varies between igneous rocks. Some igneous rocks are rich in light, light-colored minerals such as feldspar and silica. These rocks are called felsic (eg bile: feldspar, i yes: silicon). Other igneous rocks are rich in iron and magnesium compounds, so they are called mafic (but by magnesium and f for ferrum, iron in Latin).

Granite, a coarse-grained felsic intrusive rock, has the same chemical and mineral composition as rhyolite, a fine-grained extrusive rock. Basalt is a fine-grained mafic extrusive rock, it has the same chemical composition as gabbro which is a coarse-grained mafic intrusive rock that cools at depth.

Examples of igneous rocks

12 examples of igneous rocks
12 examples of igneous rocks.

Sedimentary rocks

Sedimentary rocks are rocks that form from fragments that have been cemented together. In general, sediments accumulate by forming horizontal layers, which are compacted by the pressure of materials above the layers. Materials such as silica, calcium carbonate or iron oxides are used to cement or glue the fragments.

There are three main types of sedimentary rocks:

  • Clastic sedimentary rocks: clasts are fragments of pre-existing rocks, such as clay, sand, pebbles, pebbles and cobbles. Examples of these rocks are conglomerate, sandstone, siltstone, and shale.
  • Organic sedimentary rocks: they are produced by the remains of plants and animals that accumulate and compact. An example of this type of rock is coal.
  • Sedimentary rocks by chemical precipitation: they are formed when the saturation of a material occurs in a liquid medium, forming a precipitate. Examples are dolomite, gypsum, halite (common salt) and borates.

Examples of sedimentary rocks

12 examples of sedimentary rocks
12 examples of sedimentary rocks.

Metamorphic rocks

Metamorphic rocks are rocks that result from the transformation of other rocks without melting. For example, granite metamorphoses into gneiss, limestone forms marble, and silica-rich sandstones fuse into quartzite.

Metamorphic rocks are characterized by being harder, compact and resistant and having a reoriented crystalline structure.

The process of metamorphism commonly occurs in areas of high temperature and pressure, such as in tectonic zones and at great depths.

There are two types of metamorphic rocks:

  • Foliage: presence of plates or waves of light and dark minerals, as in gneiss.
  • Not foliated: absence of plates, such as quartzite and marble.

Examples of metamorphic rocks

12 examples of metamorphic rocks
12 examples of metamorphic rocks.

You may also be interested in seeing:


Petersen, JF, Sack, Sr., Gabler, RE (2017) Physical Geography 11 ed. Cengage Learning. USA

Tarbuck, EJ, Lutgens, FK (2005) Earth Sciences – An Introduction to Physical Geology 8th ed. Pearson Prentice Hall.

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