There are different types of rocks on the planet, depending on their formation and origin. They are also classified by their physical and chemical characteristics and properties. Basically, we have the basic rock types: sedimentary, igneous, and metamorphic. Each of these rock types has further, more specific classifications.
In this article we are going to tell you about the main types of rocks that exist, their classification and characteristics.
Rock types
Sedimentary rocks
Rocks originate from the transport and deposition of material due to the action of wind, water, ice, or the chemical deposition of aqueous fluids. The definition also includes accumulations of inorganic substances, such as shells secreted by organisms. Sedimentary rocks are further divided into detrital and non-detrital rocks. To learn more about the formation of these rocks, you can consult how rocks are formed at this link.
Detrital sedimentary rocks
They were deposited from other rock fragments after a phase of transport. These rocks are classified according to the size and shape of the fragments that compose them.
Therefore, rocks with large fragments (greater than 2 mm) and rounded shapes are conglomerates, while if they are angular they are called breccias. When the pieces are loose, they are deposits called gravels. Sandstones have a medium grain size (0,06 to 2 mm) visible to the naked eye or light microscope, and silts and clays have a very small grain size (less than 0,06 mm), which can only be view with an electron microscope.
Gravel is used as an aggregate in construction, primarily to make concrete. Gravel, especially sandstone, can be used as a building stone if its durability is good.
Clay is used in many aspects of daily life . It has medicinal and cosmetic uses. It is used as a building material for making bricks and ceramics. It is also used as a raw material in the construction of mud and adobe walls and in the manufacture of traditional ceramics, earthenware, and porcelain. Due to its water-resistant properties, it can be used for absorbing contaminated products, industrial filtration, and other applications.
Non-detrital sedimentary rocks
They are formed by the precipitation of certain compounds in aqueous solution or by the accumulation of substances of organic origin. A very common type is limestone, composed mainly of calcium carbonate precipitates or accumulations of bone fragments (corals, gastropods, ostracods, etc.). The presence of these remains, which make up fossils, is often observed in these rocks. The various limestones are highly porous, calcareous tuffaceous rocks rich in plant remains, originating in rivers from the deposition of calcium carbonate on vegetation. Dolomite is another rock, different from limestone, whose chemical composition contains, in addition to carbonates and calcium, a high proportion of magnesium.
Flint is produced when the remains of the shells of organisms such as diatoms that use silica to build their shells accumulate, or when the silica is washed away by water to precipitate.
Another type of rock is evaporite, which is produced by the evaporation of water in marine and lagoon environments. The most important rock of this type is gypsum, a rock formed by the precipitation of calcium sulfate.
Limestone is a material used to make cement and lime for construction. It is also a material used in the construction of building facades and floor coverings. Plaster is used in wall cladding and in the manufacture of castings.
Coal and oil are non-clastic sedimentary rocks of organic origin because they arise from the accumulation of organic matter. Coal comes from plant remains, and oil comes from marine plankton. Given their ability to generate heat and the energy they produce through combustion, they are of great economic importance.
Igneous rocks
They are rocks that have cooled from liquid silicate components of the Earth's interior. This melt is in a high temperature state. The area near the surface (the crust) produces plutonic rocks when it cools and solidifies on its way to Earth's surface, and volcanic rocks when it cools and solidifies on the surface.
plutonic igneous rocks
Plutonic rocks originate beneath the Earth's surface. When subjected to immense pressure, their minerals bond together tightly, forming dense, non-porous rocks. They cool very slowly, allowing the mineral crystals that compose them to be relatively large. Sometimes, these crystals are visible to the naked eye.
Granite is the most common plutonic rock. It consists of a mixture of the minerals quartz, feldspar, and mica. To learn more about this type of rock, visit our section on igneous rocks.
Volcanic rocks
They originate when magma is expelled from the Earth's surface, producing lava from volcanoes and cooling to low temperatures and pressures on the Earth's surface. The result is a rock composed of a large number of small crystals or an amorphous substance (glass) that does not crystallize. Sometimes, some minerals may be surrounded by microcrystalline or amorphous material.
Volcanic rocks are usually classified according to their chemical composition. Basalt is a very common rock that is easily identified by its dark hue. Rhyolite, on the other hand, takes on a lighter shade.
Metamorphic rocks
Metamorphic rocks arise from pre-existing rocks that undergo readjustment due to a significant increase in temperature and pressure due to geological processes (burial, magma intrusion, etc.). This realignment causes changes in its mineral and chemical composition, transforming the original rock (sedimentary, igneous or metamorphic) into a new type that we call metamorphic.
The metamorphic process takes place in the solid state ; that is, the transformation occurs while the rock has never melted. Most metamorphic rocks are characterized by widespread fragmentation of the minerals, which makes them appear flattened, creating the rock's layered structure. This phenomenon is called foliation.
The slabs are made of clay, which experiences a very low increase in temperature and pressure due to burial . They have a leaf-like structure called slaty slate (very straight, parallel, and very thin leaf-like structures). They are usually black and often contain fossils. They are used for roofing tiles in construction and for covering the walls and floors of houses.
I hope that with this information you can learn more about the types of rocks and their characteristics.
