Nature is the most wondrous and enigmatic thing in the whole world. All the processes, cycles and elements being well-justified form a strong mechanism that does not need to be controlled or run by anything or anybody else but the nature itself. However, a person does not always notice all the changes that take place in nature; changes happen everywhere and all the time. If a person lives near the coast, it is not complicated to notice how the shape of the coastline alters daily, weekly, monthly, or yearly. If one lives in the interior of a continent, changes are less transparent while rivers, for instance, change their course approximately every 100 years. However, not all the changes can be easily observed by humans. While the rock cycle mainly operates underneath the ground and involves a lot of time and processes, rock appears to be one of the most mystical and impressive wonders of nature. The paper deals with the notion of the rock cycle and explains other terms, processes, and geological settings involved in the formation of all types of rocks.
The process of dynamic transitions among the main rock types is called in geology the rock cycle. Being the main concept in geology, rock cycle illustrates how rock types such as igneous, sedimentary, and metamorphic are connected with one another and how the involved processes change with the flow of time. As a result of the driving forces of the rock cycle (water and plate tectonics), rock never remains in balance and is forced to adapt to a new environment. Every type of rocks experiences particular processes that make them change their condition, geological setting or content. As a result, a new species of rock is created.
The rock cycle can be regarded as a kind or rock reincarnation while this process has a beginning, but has no end. The majority of rocks begin their cycle as igneous ones. In some time, igneous rock creates sedimentary one, which later can be either eroded and transformed into new sedimentary rock or changed into metamorphic rock. Metamorphic rocks, in their turn, can either change into sedimentary rocks or melt and become magma. Sedimentary and igneous rocks can also melt and become magma. In the end, the rock cycle starts from igneous rocks, which change first into sedimentary rocks and then into metamorphic rocks, melt back to magma, and begin the cycle again. As far as the geological setting is concerned, the rock cycle proceeds in every geological setting, starting from the deepest water points (oceans, where the seafloor reacts with seawater and forms new “hydrated” minerals) to the highest peaks, where existing rocks are eroded and transported to lower elevations by glaciation.
According to the ways of rock formation, there exist three principal classifications of rocks – igneous, sedimentary, and metamorphic.
It is a fact that the nature of every rock existing on the Earth is initially igneous. When magma, being in the state of liquid, chills and forms crystal structured rocks, igneous rocks are created. In nature, there exist different types of igneous rocks. The fact that igneous rocks are formed in fire is a distinctive feature that connects all its types.
Scientists divide igneous rocks into two contrasting categories: the ones that are cooled below the surface and the ones that are cooled on the surface. Igneous rocks that begin their lives below the surface are called intrusive rocks while the rocks that are cooled on the surface are called extrusive.
Intrusive igneous rocks, which is the most common type of rocks, are formed when “a pocket of magma slowly cools down enough to form into solid rock”. The first widely known fact about it is that every intrusive rock is created from different kinds of minerals. As soon as the liquid chills to solid, the substance crystallizes. Crystallization means that, in the process of cooling, the magma elements establish solid ties with their neighbors in an unchanging manner. Minerals are formed into bigger crystals unless they encounter other crystals. As soon as minerals are connected together strong enough not to be taken apart, intrusive igneous rock is formed. The best and the most evident example of an intrusive igneous rock is granite.
Extrusive igneous rock is one more type of igneous rocks. This type of rocks is created when magma that has reached the surface of the Earth chills and transforms into solid rock. Similar to intrusive rocks, extrusive ones also have small-grained crystals. However, the crystals are so minor that a person cannot see them. Depending on the kind of lava that formed the rock and on the time of cooling, extrusive igneous rocks can be divided into different types. Three basic types of volcano produce three corresponding kinds of extrusive rocks.
Examples: obsidian (Glass Mountain; a large obsidian flow at Medicine Lake Volcano), pumice (Mount St. Helens, Washington), rhyolite ( The Thuringian Forest, Germany; Indiana Rock, Oakland), andesite (Andesite Mount Žarnov, Slovakia), basalt (Yellowstone National Park, USA), granite (Roche Rock, Cornwall, England), diorite (Cretaceous diorite rock outcrop near Boca Ketu, Aruba), gabbro (Rock Creek Canyon, eastern Sierra Nevada, California), porphyry (East African Rift, including Mount Kilimanjaro), pegmatite (White Elephant Mine in the Black Hills, South Dakota), scoria (Maungarei in New Zealand).
In the course of time, igneous rocks are destroyed by water and wind. Small rock particles find their way to the bottom of seas, streams, lakes, rivers, and oceans. As a result, the layer of sediment on the bottom of the water formations expands. The sediments’ weight becomes so immense that they start pushing the lower layers of sediment with enormous force. As a result, with the help of minerals that help to bond sediments together, sedimentary rock is created. Scientists differentiate four basic kinds of sedimentary rocks such as clastic, chemical, biochemical, and other.
Clastic sedimentary rocks are the rocks created out of separated particles of rocks. According to the shape of pieces that form the rock and their size, sedimentary rocks are divided into: conglomerates, sandstone, siltstone, mudstone, and breccias.
Remains of living organisms form biochemical sedimentary rocks. For instance, dead animals’ shells that are made of calcium form limestone. After animal’s death, calcium combines with different components and minerals and solidifies into rock. Fossils, coal, chart and coquina serve as the examples of this type of rock.
Chemical sedimentary rocks are produced when water vaporizes and minerals that retain solidify into rock. An unbelievable sample of this sort of rock is salt. Accordingly, when a person eats salt, he/she eats a stone called halite.
Another kind of sedimentary rocks is extremely infrequent, being usually the result of asteroid’s impact. An asteroid hits so hard that it separates rock and its pieces float together into another sedimentary rock. Another illustration is hot rock erupted from a volcano, however, not so hot that it can melt the rock it assaults. As a result, it hardens around other pieces of rock, producing another sedimentary rock.
Examples: breccia (Titus Canyon Narrows, Death Valley National Park, California), chert (Ouachita Mountains of Arkansas, Oklahoma), coal (coal mine in Wyoming, the United States), conglomerate (Carmelo Formation/Conglomerate at Point Lobos), dolomite (Dolomite rock, Japan), flint (Norfolk, England on the beaches at Beeston Bump and West Runton), limestone (Limestone in Waitomo District, New Zealand), rock salt/halite (Jurassic rock, Carmel Formation, Utah), sandstone (Devonian Sandstone at Suur Taevaskoda, Estonia).
Metamorphic rocks are produced deep under the surface when pressure and heat are used either to igneous or sedimentary rocks. Pressure and heat affect rocks so that they substantially change their structure. As a rule, metamorphic rocks are formed from various rocks. Marble, for instance, is created when limestone or dolomite is heated for many thousands of years. Gneiss is formed form igneous rocks like granite, schist and from sedimentary like mudstone or siltstone, and slate from shale.
There exist three different ways how heat and pressure influence rocks: regional, contact metamorphism, and tectonic process. The most common way of metamorphism is the regional one while it is the easiest one. It happens when rocks get buried by new rocks created on top of them.
Examples: quartzite (the Prospect Mountain Formation on top of Jeff Davis Peak in Nevada, the United States), marble (Marble wall of Ruskeala. Republic of Karelia, Russia), slate (Slate Cedar Point quarry, on Lake Bomoseen, Castleton), phyllite (Dalradian metasediments of northwest Arran), schist/soapstone (Moine Schist, Scotland), gneiss (Loch Laxford, Scotland), hornfels (Hornfels Rock, Japan), novaculite (Novaculite flatirons in the Marathon Uplift), anthracite (Culm pile, Pennsylvania, the USA), serpentine (Serpentinite outcrop on the coastal bluffs of the Presidio).
To conclude, igneous rocks are considered to be the most prevalent rocks that form the crust of the Earth. Moreover, igneous rocks always stand at the beginning of every rock cycle. Although sedimentary rocks form only around 8 percent of the Earth’s rocks, they are extremely important. They store the history of life on the Earth, containing fossils and being formed of the most ancient rocks on the bottom and the newest ones at the top. Metamorphic rocks, in their turn, prevail on the continental plates. All in all, the way rocks are created consists of many natural processes working without failures. Therefore, they can undoubtedly be considered one of the nature wonders. Having an everlasting, eternal nature, the rock cycle can be understood and considered as the reincarnation of rocks.