We know that different types of rocks exist on our planet, depending on their origin and characteristics. These include sedimentary, igneous, and metamorphic rocks. These three types of rocks are distributed throughout the Earth's crust. However, many people don't know how rocks are formed.
Therefore, we are going to dedicate this article to telling you how rocks are formed step by step, what their characteristics are at their origin and the importance of these processes.
Rocks, crystals and minerals
The rocks you see around you—mountains, canyons, and riverbeds—are made of minerals. A rock is composed of two or more minerals. You need minerals to make rocks, but you don't need rocks to make minerals. All rocks are made of minerals; all parts of a mineral are made of the same substance . If you were to cut a sample of a mineral, it would look the same throughout. There are approximately 3.000 different minerals in the world. Minerals are made up of chemical elements, either a single element or a combination of elements. There are 103 known chemical elements.
Crystals are minerals that have a chance to grow in a predetermined way. The chemical elements that make up a mineral determine the forms that they can have. We can talk about different minerals from the crystalline forms they have.
Minerals sometimes form in spaces with very little room, so they don't have a crystalline shape. When a mineral has a large mass, it is called a massive mineral. If it has a well-defined shape, with easily visible flat sides and edges, it is called a mineral crystal.
Most of the crystals on Earth formed millions of years ago. Crystals form when liquid rock inside the Earth cools and hardens. Crystals sometimes form when subsurface fluids move between fractures and slowly deposit minerals. Most mineral crystals take thousands of years to "grow," but some like salt form so fast that you can watch them grow at home.
When rocks break into smaller and smaller pieces, they become sand. If you look at sand under a microscope, you'll see that it's made up of the same minerals as the rock it came from. When a plant begins to sprout in the sand, it transforms small rocks into soil.
how rocks are formed
Rocks are constantly forming, being deposited, and sinking, and then reforming again and again. This is called the rock cycle. It's like the water cycle, but over a much longer period of time. For rocks, this change takes thousands and millions of years. You can learn more about this process in our article on the rock cycle.
Erosion
Erosion is a key part of the rock cycle. It is responsible for shaping much of the interesting landscape around us. This is also a significant issue, as people live in large numbers in various areas and use the environment in different ways. There are things people can do to increase or decrease erosion. Erosion is primarily the result of weathering.
Water causes significant erosion. When it falls as acid rain, it can dissolve acid-sensitive rocks. Marble and limestone can deteriorate when exposed to rain. Floods occur when rainfall is very heavy, such as during monsoons. Swollen or overflowing rivers can cause landslides and erode riverbanks.
The action of waves on the beach can cause a lot of erosion. Waves crash against the rocks, and occasionally, cliffs collapse . This is why you often find small pebbles in the beach sand. Strong currents, like those found in fast-flowing mountain rivers, or huge waves on the coast, can cause rocks to roll. This causes the sharp edges of the rocks to be worn down, which is why river rocks, as well as beach stones, appear smooth.
From time to time, mountains collapse due to the freeze-thaw cycle, with large rocks crumbling into smaller ones. When water enters cracks in the rock, the volume of that water increases during the freezing cycle, making the cracks larger. When the cracks fill with water during the thaw, it allows more water to seep deeper into the rocks, causing them to break apart when they refreeze.
As the wind carries sand and dust, it can erode layers of rock. The wind can easily break up fine sand and then use this sand to strike rocks in its path. Sometimes, only layers of soft rock are eroded, leaving interesting shapes. This type of erosion usually only occurs in very dry areas, such as deserts.
How igneous rocks are formed
New igneous rocks are created when volcanoes erupt and molten rock rises to the Earth's surface. When rock is in a liquid state inside the Earth, it is called magma. When magma hardens within the Earth's crust, it becomes granite. Most mountains are made of granite. For a more in-depth exploration of igneous rocks, you can consult our article on igneous rocks.
When mountains first formed, they were tall and jagged, like the Rocky Mountains on the west coast of North America. Over time (millions of years), mountains become ancient mountains, like the Appalachians on the east coast of the United States. As they age, they become rounded and lose a lot of height. What happens during this time is that parts of the rock are torn away by erosion. Rain, freeze-thaw cycles, wind, and running water are slowly destroying the mountain.
How sedimentary and metamorphic rocks are formed
Eventually, most of the upper rock fragments fall into downslope rivers and streams. These small pieces of sand and rock are called sediments.
When the flow of water slows down, these sediments settle to the bottom of the lake or ocean into which it flows. Over many years, layers of different rocks settle to the bottom of lakes and oceans. Eventually, the layers of sandy soil at the bottom of lakes and oceans harden into rock. These are called sedimentary rocks.
Metamorphic rocks are rocks that have changed. The word comes from the Greek words "meta" and "morph," meaning to change shape. Metamorphic rocks are originally igneous or sedimentary rocks, but they have changed due to the movement of the Earth's crust. As the crust moves, the rocks are compressed, and the heat causes them to deform.
I hope that with this information you can learn more about how rocks are formed and their characteristics.
