Types of Rocks: Igneous, Sedimentary and Metamorphic Rocks

Types of Rocks: Igneous, Sedimentary, and Metamorphic Rocks

The characteristics of each mineral are combined in aggregates to form rocks. The phrase "rock type" can refer to any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics.

There is a specific classification scheme for each important type of rock. Rocks come in a wide variety in the natural world.

Rarely do natural rocks have such basic characteristics, and they typically exhibit some variation in the characteristics as the measurement scale is changed.

Types of Rocks

Rocks come in three different varieties:

  • Igneous Rocks
  • Sedimentary Rocks
  • Metamorphic Rocks

Igneous Rocks:

  • Any igneous rock's magma is its core. In addition to gases and other volatile substances, magma is made up of a mixture of molten or semi-molten rock.
  •  The temperature rises as you descend further underground; if you keep going, you'll eventually reach the Earth's mantle, a thick solid rock surrounding the planet's core.
  • When molten rock—rock liquefied by extreme heat and pressure—cools to a solid state, it solidifies into igneous rocks, classified as this type of rock.
  • At volcanic centres, lava is the molten rock that flows out of fissures or vents; when it cools, it solidifies into rocks like basalt, rhyolite, or obsidian. Ashes, bombs, tuffs, and volcanic breccias are just a few of the fragmented materials ejected into the air during a volcano eruption and collected as pyroclastic deposits.
  •  Igneous rocks are called primary rocks because they are the first rocks in the rock cycle to form from magma.
  • Examining a rock's texture, density, colour, and mineral makeup can quickly determine whether it is igneous. The texture of the rock is influenced by its size, shape, cooling and solidification processes, and the distribution of crystallinity within the rock.

Igneous rock Texture

A rock's texture describes its parts' sizes, shapes, and arrangements.

Rule of Thumb

The size of the mineral crystals in igneous rocks may indicate how quickly the lava or magma cooled before solidifying into the rock. The number of gases or the availability of the chemicals needed to form crystals in the molten rock can also impact crystal size.

Larger crystals typically indicate intrusive igneous rocks. Smaller crystals typically indicate faster cooling when it comes to extrusive igneous rocks.

Types of Igneous Rock Texture

  • Aphanitic: fine-grained, less than 1 mm, grains not seen with the unaided eye.
  • Phaneritic: “coarse-grained”; visible crystals; 1 to 10 mm
  • Pegmatitic: "very coarse-grained"; > 1 cm
  • Porphyritic: composed of large and fine-grained crystals; the large crystals are called phenocrysts, and the background is the matrix.
  • Vesicular: rocks that have vesicles resembling a sponge (e.g. scoria and pumice)
  • Pyroclastic: fragmented, angular grains ejected during the eruption (e.g. volcanic breccia)
  • Glassy: when lava cools quickly, there is not enough time for large mineral crystals to form (e.g. obsidian)

Characteristics of Igneous Rocks

  • There are no fossilized deposits in igneous rocks. Any fossils that may have existed deep within the crust are destroyed when they erupt from the Earth's surface due to the heat these rocks generate.
  • The majority of igneous forms contain multiple mineral deposits.
  • Glassy or coarse are both possible.
  • Normally, these don't react with acids.
  • Mineral occurrences come in the form of varying-sized patches.

    Types of Igneous Rocks

According to the conditions under which they cool, igneous rocks can have a variety of aesthetic qualities as well as different compositions. Rocks classified as extrusive and intrusive are the two main types of igneous rocks.

  • Intrusive Igneous Rock: Rocks that are intrusive igneous are those that crystallize slowly and produce large crystals as they cool. Intrusive igneous rocks include pegmatite, granite, and diorite.
  • Extrusive Igneous Rock: Rapid cooling produces small crystals in extrusive igneous rocks, which are rocks that erupt onto the surface. Some rocks cool so quickly that an amorphous glass forms as a result. Some examples of extrusive igneous rock include basalt, tuff, and pumice. 

Sedimentary Rocks: 

Existing rocks or pieces of extinct organisms that have accumulated on the surface of the Earth over time form sedimentary rocks. Sedimentary rocks are produced due to the compression and cementing of deep sediment burial.

How Do Sedimentary Rocks Develop?

The deposition of material at the Earth's surface within bodies of water, followed by cementation, forms sedimentary rocks. These rocks are created in four different ways:

  • Weathered remnants of other rocks being deposited
  • Sediment accumulation and consolidation
  • Resultant biogenic activity's deposition
  • Precipitation from the remedy.

Types of Sedimentary Rocks

Three categories are used to categorize sedimentary rocks: 

  • Organic Sedimentary Rocks: Due to the accumulation and deposition of dead plants and animals in rock layers, this type of rock is primarily composed of coal and limestones.
  • Clastic Sedimentary Rocks: This type of rock is created when different rock types are mechanically weathered to form rock layers.
  • Chemical Sedimentary Rocks: This kind of rock is produced by a chemical reaction that causes naturally occurring minerals to cool over time as precipitates before returning to their original rock form.

Uses of Sedimentary Rocks

The majority of structures and monuments use sedimentary rock. The list below includes a few applications for this kind of rock.

  • Cement is produced using limestone.
  • Building stones include sandstone and limestone.
  • Glass is made from quartz, a type of sedimentary rock.
  • Plaster is produced using rock gypsum. 
  • Natural gas, oil, coal, uranium, and other energy resources are created in sedimentary rocks.

Facts about Sedimentary Rock

Sediment is deposited over time, resulting in the formation of sedimentary rocks. Here are some interesting facts about sedimentary rocks.

  • The mineral quartz is found in hard, sedimentary forms such as flint.
  • Most of the Earth's rocky surface is composed of sedimentary rocks, but these rocks only comprise a very small portion of the planet's crust.
  • They frequently have fossilized plants and animals that are millions of years old.
  • The fossilized remains of marine life that perished millions of years ago are frequently used to create limestone.
  • In exposed cliffs, these layers of rock, known as strata, are frequently visible.

Metamorphic Rocks: 

Metamorphic rocks are created when rocks undergo numerous physical changes, such as pressure, heat, and chemical activity. When igneous or sedimentary rocks experience physical processes like pressure exposure, temperature changes, and tectonic plate movement at the plate boundaries When exposed to an environment, these rocks undergo these changes.

Types of Metamorphic Rocks

  • Foliated Metamorphic Rocks: These rocks exhibit an arrangement of some mineral grains that resemble parallel stripes. When a rock is compressed under pressure, the minerals inside align in an elongated or flat pattern known as foliation. The sheet-like structure of these rocks reflects the direction of pressure.

Granite, gneiss, and biotite schist are foliated metamorphic rock types. 

  • Non-Foliated Metamorphic Rocks: Minerals that are not flat or elongated are used to create these rocks. In this case, applying pressure won't cause the grains to align. Non-foliated metamorphic rocks do not have layered or banded appearances.

Skarn, novaculite, marble, hornfels, and quartzite are foliated metamorphic rocks.

Characteristics of Metamorphic Rock

  • Along with tectonic plate faults, cataclastic metamorphism occurs when rocks rub against one another, reducing the grain size.
  • These rocks cannot be transformed into a non-foliated rock, and their transformation is regarded as low grade.
  • Numerous mineral water chemical reactions caused by the movement of rock produce a variety of precious metals and gemstones.