Rock Cycle – Steps Involved in Rock Cycle

Earth Materials and Systems – Rock Cycle

The cycling of matter such as rock, magma, water, ice, gases, and living things and their remains drives both processes like the rock cycle and water cycle. As they move between the Earth’s surface and its internal layers, rocks and matter undergo uplift, weathering, erosion, deposition, melting, crystallization, and metamorphism. Water particles go through evaporation, condensation, precipitation, and flow as part of the water cycle.

Matter can change physically and chemically as it moves through these cycles. A physical change is frequently accompanied by a change in the state of matter, such as melting, crystallization, evaporation, or condensation. Folding, faulting, breaking, physical weathering, transport, and deposition are all examples of physical changes. Chemical reactions occur when rock, water, and air come into contact, as in the process of chemical weathering.

Rocks

A rock is a solid and hard object made up of different minerals. Minerals are naturally occurring, non-living things. Minerals are the main unit of rocks. Normally, rocks are not made up of particular structures or substances that can be described by any scientific formula. So, scientists generally categorize rocks by their method of formation.

Rocks are classified into three types: metamorphic rock, igneous rock, and sedimentary rock. Water, rock, nitrogen, and oxygen are all recirculated- circulated between the environment and living things. The existing material should cycle consistently to support life. If the matter does not cycle continuously, then the Earth cannot support life.

As matter goes all the way through the cycles of the Earth’s system, the matter changes over time and the Earth’s surface also varies. Some of the processes in the cycle take millions of years. For example, the formation of mountains. The rock cycle also takes many years.

Rocks are formed by three processes: igneous, metamorphic, and sedimentary. Any rock can convert into any new type of rock. The rock cycle obtains energy both from internal (convection currents, see the plate tectonic cycle above) and external sources (the sun).

Rock Cycle

The rock cycle refers to the sequence of processes by which rock changes from one form to another, is destroyed, and is formed again by various geological processes. This entire process takes many years.

Melting, cooling, heating, weathering, erosion, heat, and pressure are all part of the rock cycle.

Weathering is the process by which rock is cracked down into smaller pieces as a result of changes in wind, water, and temperature.

The flow of weathered rock from one place to another by wind, water, ice, or gravity is known as erosion.

During the rock cycle, rock forms deep within the earth, occasionally moving, changing, and coming to the earth’s surface before returning to the earth’s interior. The three types of rocks move through the cycle in different ways.

The Three Major Rock Types

Earth’s rocks can be classified as per the processes that created them:

Steps Involved in the Rock Cycle

Rocks may see several ways in the rock cycle. For example: When rock is exposed to weathering or erosion, igneous rock changes to sedimentary rock. Under severe heat conditions, igneous rock changes to metamorphic rock. The path that rocks follow in the rock cycle is seen by the forces acting on it.

The three most important methods that can change the rock are given below:

1. Cooling and Crystallization:

Deep inside the earth, the temperatures are very high, which creates magma. Magma is in liquid form. Sometimes, magma that reaches the earth’s surface is called lava. The magma may reach to earth’s surface by a huge explosion through a volcano, or sometimes it comes out slowly through the cracks. As magma cools, crystals grow to form igneous rock. The formation of crystals from magma is called crystallization.

Igneous Rock:

Its formation starts as magma, or molten rock, and solidifies/crystallizes as it cools in one of two completely distinct environments.

Extrusive igneous rocks formed by volcanic processes, such as basalt, cool quickly on or near the Earth’s cold surface and form rocks with a fine crystal structure.

Intrusive igneous rocks, on the other hand, cool slowly in well-insulated plutons (a mass of igneous rock – Pluto was the Roman god of the Underworld) deep beneath the Earth’s surface, forming rocks with large crystals, such as gabbro.

Gabbro is a mineral that has the same chemical composition as basalt but a different crystalline structure.

Examples of igneous rocks:

2. Weathering and Erosion:

Rocks wear down by water, wind, ice, and even by plants and animals. Over time, wind, water, and ice can break down larger rocks into sediments. The method of breaking down rocks is called weathering. Moving water, wind, and glaciers take these pieces of rocks from one place to a new place. This is known as erosion.

The sediments are dropped somewhere and deposited. This is referred to as sedimentation. The sediments can then be compressed and glued together just to form a sedimentary rock (compaction + cementation = lithification). This entire process could take hundreds or even thousands of years.

Sedimentary Rocks:

Sedimentary rocks are mostly composed of clasts, which are pieces of other rocks that have broken off (or grains). Large rocks are broken down into clasts by weathering, which are then transported (eroded) by wind or water and deposited in a basin.

After some time, the clasts are lithified (lithos is the Greek word for stone) through compaction and cementation processes. Clastic sedimentary rocks are classified according to the size of the clasts that formed them; sandstone, siltstone, and mudstone, for example, are made up of smaller and smaller clasts (see table below).

Gravel, or clasts ranging in size from 2 to 4000 mm, when mixed with tiny particles, can lithify and form conglomerates (if the gravel is rounded, such as that found in riverbeds) or breccias (if the gravel is angular and sharp-edged, such as that found at the bottom of a mountain slope).

Furthermore, some rocks are formed when minerals crystallize or precipitate out of solution or pile up in the bodies of living organisms in a basin, resulting in chemical and biogenic sedimentary rocks.

3. Metamorphism:

Metamorphism is defined as “changing form.” Metamorphism occurs within the crust when rock is exposed to extreme temperatures and pressures. The entire rock does not melt with metamorphism, the rock changes as a result of extreme conditions of heat and pressure. A metamorphic rock may contain a new structure or texture of mineral.

The rock cycle does not have any starting point or end. It keeps on continuing. The different procedures involved in the rock cycle take place for hundreds, thousands, or even millions of years. Even though we say rocks are solid and unchanging, they slowly keep on changing all the time to various factors.

Metamorphic Rock:

Metamorphic rocks are formed when igneous, sedimentary, or other metamorphic rocks are subjected to extreme temperatures and pressure during burial or contact with intrusive or extrusive magma, causing changes in the mineral composition and texture of the rock (“meta” means change, and “morph” means form).

These induced changes include (i) the formation of new minerals at the expense of old minerals and (ii) altered rock texture as a result of changes in the size, shape, and orientation of mineral crystal structures. Quartzitic sandstone, for example, is metamorphosed to quartzite; the individual quartz grains recrystallize with the former cementing material to form an interlocking mosaic of quartz crystals, and most of the sandstone’s original texture and sedimentary structures are lost.

Regional metamorphic rocks are formed over large areas, primarily as a result of pressure, as seen at convergent plate boundaries. Contact rock metamorphism, on the other hand, is thermally driven and occurs frequently along the boundaries of igneous intrusions or beneath lava flow zones.

Steps to Remember in the Rock Cycle:

First, lava erupts from a volcano and cools into an igneous rock. Over a period, this igneous rock is weathered by the effect of wind and rain, which changes the rock into small pieces called sediments. These sediments are transported by wind and water, by erosion, and get accumulated. Following deposition, these sediments can be compacted and cemented into sedimentary rock. Tectonic activity causes the sedimentary rock to be buried deep within the Earth over time.

The pressure and heat from the inside of the Earth change the structure of the rock, transforming it into a metamorphic rock. This metamorphic rock is buried deeper and deeper until it becomes so hot that it melts into magma. The magma then explodes as lava from a volcano and cools as an igneous rock. The cycle starts again.

Selected Processes and Landforms Related to the Rock Cycle

1. Alluvium: Loose, unconsolidated (not cemented together into a solid rock) sediment eroded, reshaped, and deposited by flowing water in a riverbed, floodplain, or delta (non-marine environment). Clasts are usually well-rounded and sorted (equal in size) – form conglomerates when lithified.
2. Cementation: The process of lithifying clastic sediment through the precipitation of mineral cement among the sediment grains.
3. Colluvium: Loose sediment transported by gravity at the bottom of a slope or against a barrier on that slope. When lithified, angular, sharp-edged, and unsorted clasts form breccias.
4. Compaction: Tighter packing of sedimentary grains that results in weak lithification and a decrease in porosity, typically caused by the weight of overlying sediment.
5. Crystallization: The method by which specific minerals in a solution or melt form solid, segregated crystals is known as crystallization.
6. Deposition is the process by which sediments settle out of a transporting medium in a basin.
7. Erosion: It refers to the processes that loosen weathered clasts and transport them across the Earth’s surface. Water, ice, wind, and gravity are all erosion agents.
8. Lithification: The process of converting sediment into sedimentary rock. Compaction and cementation are both parts of this process.
9. Magma: A molten rock that is typically a silicate melt with suspended crystals and dissolved gases. When magma erupts from a volcano, it is referred to as lava.
10. Metamorphism: It is the alteration of a rock’s minerals and textures caused by changes in temperature and pressure, as well as the gain or loss of chemical components.
11. Sediment: Material (such as gravel, sand, mud, and lime) transported and deposited by wind, water, ice, or gravity; precipitated from solution; organic deposits (such as coal and coral reefs).
12. Subduction: The movement of one tectonic plate beneath another at a converging boundary and sinking into the mantle.
13. Weathering: The chemical or physical breakdown of rocks as a result of exposure to atmospheric agents and pressures and temperatures at or near the Earth’s surface, with little or no transportation of the loosened or altered materials.
14. Xenolith: A xenolith is a pre-existing rock fragment that becomes encased in a larger rock during its development and hardening.