The Formation of Igneous Rocks: A Geological Explanation

Introduction

Understanding our planet is has been one of the greatest achievements for humanity, even if there is a lot that we still don’t know, our understanding of our surrounding help us realize the history and composition of our planet, this has been a main goal for science and has been divided on different fields of study for example Physics, Chemistry and Biology; there is so much that we know now thanks to the hundreds of years of study and research done into these different fields, but there is a branch of science that focus on the origin, composition and history of Earth as well as the chemical, biological and physical forces in and outside the planet and is called Geology. In essay about how rocks are formed will be revealed the nature of rocks and the main job of a geologist.

Geologist comprehend the history of Earth throughout the study of rocks, minerals and events like earthquakes, that helps them have a better understanding of the past of the planet, the continents and the oceans and also have an idea of the future. 

Rocks

A rock is an inorganic solid created naturally, containing different minerals, and can be classified because of it and the way it was formed. There are three types of rocks and this are named after their origin: Igneous, Sedimentary and Metamorphic. 

• Igneous rocks their name is derived from the Latin word Ignis that means fire, this are formed from magma in a process of cooling that end up is the solidification of this and giving different proprieties depending on different factors such and rate of cooling, minerals, etc.
• There are rocks that are found very deep in Earth and are subject to heavy heat and pressure causing metamorphosis which means these may change into different rocks, this are called Metamorphic rocks.
• And we have the Sedimentary rocks that are from by older rocks crushed into pieces called clastic sediments such as gravels, sand, clay, and different chemicals. This is the name given to rocks formed by existing rocks weathered , moved, creating sediments.

Igneous Rocks

In how rocks are formed essay attention will be focused precisely on the first type of rocks. Igneous rocks are classified by the minerals contained by the rocks, which helps geologists to have an idea of the composition of the magma the rock came from. For example, when an Igneous rock contains a high amount of silicic acid is a clue which indicates the composition of the magma of origin in this case acidic. Also depending on the mineral composition of the rock we have a classification based on the colours of the main mineral that compose the rock for light colours the term used is Felsic base on the dominant mineral on the light group quartz and feldspars and for dark colours Mafic base on the dominant dark minerals magnesium and iron. 

The second more important characteristic for the classification of Igneous rocks is the grain size. The difference in grain size on the rock is due to the variation on the cooling rate of the magma, at a very rapid rate of cooling small crystals and glass is created on the contrary a slow cooling manga generated larger crystals, one of the variables that can contribute on the cooling rate of the magma can be the way the magma is exposed to the surface , can be a big explosion sending magma to high altitudes causing a very quick cooling. To classify the Igneous rocks, we have that depending on grain size the rocks are divided into:

1. Coarse-grained (Average>5)
2. Medium-grained (1-5mm)
3. Fine-grained And depending on the darkness of the mineral into:

• Acid: Abundance of silica and other elements forming quartz, light mineral composes a large proportion of the rock
• Intermediate: Lower proportions of silica and quartz are either absent or in small proportions
• Basic: Even lower proportions of silica and contains ferro-magnesian minerals giving a dark colour. 

One big formation of Igneous rocks is the Kangaroo point cliffs which is one of the main attractions in the Brisbane City in Queensland, Australia. But this formation of rock was created by a natural event that is extremely rare.

Kangaroo Point Cliffs

The Kangaroo point cliffs are a formation of igneous rock developed from quarrying building stone in the 1970s by female prisoners which mined the rock. Is known that this rock was formed because of a change in temperature due to the horizontal jointing, and as mentioned before Igneous rocks are formed after magma has experienced a change in temperature, but since this rocks are not crystalline geologist have come to a conclusion that is was created by a pyroclastic flow which means it was not lava that solidified but ash.

When ash solidifies creating rocks these are usually soft, on the contrary the cliffs are extraordinarily strong this is because the eruption of the stratovolcano was horizontal instead of vertical causing the ash and the minerals that came out of it to be welded together. This sort of flow is given the French name Nuée Ardente, another example of this flow the was the Mount Pelée eruption in 1902 for which the term was revived by French geologist Alfred Lacroix to describe gas clouds. This type of flow is extremely rare and the type of rock which form the cliff is not found any were else .

The assumption of the horizontal flow and the ash eruption Is supported by the air bubbles and the xenolith that can be seen on the cliff, these must have been trapped under the ash and then when it solidified became part of the rock and are visible on the face of the cliff.

Conclusion

In essay about rocks, what types of rocks exist were briefly considered, attention was focused on Igneous rocks that are formed from magma. Also there was presented an example of the cliff that is formed from Igneous rocks - the Kangaroo point cliff.

References

• Baker-Blocker, A., 2018. Geology and the extraction of natural resources. Salem Press Encyclopedia of Science, p. 3.
• Gosman, G., 2013. What do we know about rocks?. Illustrated edition ed. s.l.:Powerkids Pr.
• Park, G., 2006. Introducing Geology: A Guide to the World of Rocks. 3rd edition ed. s.l.:Dunedin Academic Press.
• Salmon, V. L., 2019. Mount Pelée Erupts.. Salem Press Encyclopedia, p. 3.
• Willmot, W., 2004. Rocks and landscapes of the national parks of southern Queensland. Sydney: Geological Society of Australia Inc.
• Woodhouse, D., 2018. Geology for Environmental Engineers. New York, New York: Momentum Press LLC.