20+ Types Of Rocks

We have researched on different Types of rocks in the world, main group and so much more.

What Is A Rock?

According to Wikipedia, A Rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter.

It is categorized by the minerals included, its chemical composition and the way in which it is formed.

Rocks form the Earth’s outer solid layer, the crust, and most of its interior, except for the liquid outer core and pockets of magma in the asthenosphere.

Rocks are usually grouped into three (3 types of rocks) main groups:

igneous rocks, sedimentary rocks and metamorphic rocks.

1. Igneous rocks are formed when magma cools in the Earth’s crust, or lava cools on the ground surface or the seabed.

2. Sedimentary rocks are formed by diagenesis or lithification of sediments, which in turn are formed by the weathering, transport, and deposition of existing rocks.

3. Metamorphic rocks are formed when existing rocks are subjected to such high pressures and temperatures that they are transformed—something that occurs, for example, when continental plates collide.

20+ Types Of Rocks

Types Of Rocks
3 Types Of Rocks

• Igneous Rock

Igneous Rock or magmatic rock, is one of the three main (3) types of rock , the others being sedimentary and metamorphic.

Igneous rock is formed through the cooling and solidification of magma or lava.

The magma can be derived from partial melts of existing rocks in either a planet’s mantle or crust.

Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.

Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks.

Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses.

Igneous rocks occur in a wide range of geological settings: shields, platforms, orogens, basins, large igneous provinces, extended crust and oceanic crust.

• Granite Rock

Granite is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase.

It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground.

It is common in the continental crust of Earth, where it is found in igneous intrusions.

These range in size from dikes only a few centimeters across to batholiths exposed over hundreds of square kilometers.

• Basalt Rock

Basalt is an aphanitic extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon.

• Marble

Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite.

Marble is typically not foliated, although there are exceptions. In geology, the term marble refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone.

• Sandstone Rock

Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.

• Slate Rock

Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism.

It is the finest grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression.

• Limestone Rock

Limestone is a common type of carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).

Limestone forms when these minerals precipitate out of water containing dissolved calcium.

This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years.

Limestone often contains fossils, and these provide scientists with information on ancient environments and on the evolution of life.

• Shale Rock

Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.

Shale is characterized by its tendency to split into thin layers (laminae) less than one centimeter in thickness.

• Gneiss Rock

Gneiss is a common and widely distributed type of metamorphic rock.

Gneiss is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks.

Gneiss forms at higher temperatures and pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage.

• Schist Rock

Schist Rock is a medium-grained metamorphic rock showing pronounced schistosity.

This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes or plates.

• Conglomerate Rock

Conglomerate is a clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts.

A conglomerate rock typically contain a matrix of finer grained sediments, such as sand, silt, or clay, which fills the interstices between the clasts.

• Gabbro Rock

Gabbro is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth’s surface.

Slow-cooling, coarse-grained gabbro is chemically equivalent to rapid-cooling, fine-grained basalt.

Much of the Earth’s oceanic crust is made of gabbro, formed at mid-ocean ridges. Gabbro is also found as plutons associated with continental volcanism.

Due to its variant nature, the term gabbro may be applied loosely to a wide range of intrusive rocks, many of which are merely “gabbroic“. By rough analogy, gabbro is to basalt as granite is to rhyolite.

• Diorite Rock

Diorite is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals.

It is intermediate in composition between low-silica (mafic) gabbro and high-silica (felsic) granite.

• Obsidian Rock

Obsidian rock is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock.

• Quartzite Rock

Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone.

Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts.

Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite.

Other colors, such as yellow, green, blue and orange, are due to other minerals.

• Intrusive Rock

Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form intrusions, such as batholiths, dikes, sills, laccoliths, and volcanic necks.

Intrusion is one of the two ways igneous rock can form. The other is extrusion, such as a volcanic eruption or similar event.

An intrusion is any body of intrusive igneous rock, formed from magma that cools and solidifies within the crust of the planet.

In contrast, an extrusion consists of extrusive rock, formed above the surface of the crust.

• Pumice

Pumice called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals.

It is typically light-colored. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker vesicle walls, and being dark colored and denser.

• Andesite Rock

Andesite is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite.

It is fine-grained (aphanitic) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende.

• Chert

Chert is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2).

Chert is characteristically of biological origin, but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood.

• Breccia

Breccia is a sedimentary rock composed of broken fragments of minerals or rocks cemented together by a fine-grained matrix.

• Sedimentary Rock

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth’s surface, followed by cementation.

Sedimentation is the collective name for processes that cause these particles to settle in place.

• Coal

Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams.

Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.

Coal is formed when dead plant matter decays into peat and is converted into coal by the heat and pressure of deep burial over millions of years.

• Dolomite Rock

Dolomite (also known as dolomite rock, dolostone or dolomitic rock) is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite, CaMg(CO3)2.

It occurs widely, often in association with limestone and evaporites, though it is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 65 million years in age).

The first geologist to distinguish dolomite rock from limestone was Belsazar Hacquet in 1778.

• Hornfels

Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable.

For more info on Rocks, visit our blog category on Rocks and feel free to drop your review on these types of rocks in the comments section

Add a Comment

Your email address will not be published.