Free «The Rock Cycle» Essay Sample

Ideally, rock cycle is a continuous phase of changes. For instance, igneous rock may change into metamorphic rock or into sedimentary rock. On the other hand, sedimentary rock can change either into metamorphic rock or into igneous rock, whereas metamorphic rock may change into sedimentary or igneous rock. In essence, igneous rock is formed when magma cools and forms crystals.

According to Allen (2010), rocks undergo several cycles in order to yield the different types of rocks. The raw materials of rocks are magma from volcanic activity and organic material. The accumulations of these raw materials over a certain period yield the different types of rocks.

Magma from the centre of the earth plays a major role in the formation of rocks. Sedimentary rocks can however be formed through accumulated organic material. Magma is known to have come from light weighted rocks that slipped into the part of the earth known as the mantle (Morgan, 2010). Plate tectonics is known to have played a major role in this displacement.

The whole process begins from the eruption of magma. Basically, igneous rocks are formed from magma that has cooled over time. Rapid cooling of the magma yields small crystals and this is known as an extrusive igneous rock. This rapid cooling can only happen at the earth’s surface where there is free flow of air hence the name extrusive (Morgan, 2010). Slow cooling of magma yields larger crystals and hence the name intrusive igneous rocks. These types of rocks are found deep in the earth, and contain valuable minerals.

Igneous rocks are easily identifiable due to their exclusive characteristics. Some of these characteristics are; the minerals are arranged in no particular pattern, they have crystals of varying sizes and this rock is usually very hard. Some of these characteristics are absent in other types of rocks such as the sedimentary rocks, which are usually not very strong (Brotzge, 2009). 

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Specimen 98031 is a type of igneous rock that contains medium coarse grain measuring about nine millimeters in width. This means that this rock did not form very deep near the earth, but somewhere in between. The conditions must have allowed some free flow of air. During the cooling of magma, air improves the rate of crystal formation (Brotzge, 2009). Thus the rock can be classified as an intrusive igneous type of rock. It is composed of feldspar and quartz, which are more of alkaline materials.

This category of rock is known to be formed through a method known as fracture propagation (Allen, 2010). The centre of the earth rather known as the core is known to have very high temperatures. As such, magma is at a very high temperature as well as pressure. Magma that is meant to form granite is also very buoyant (Brotzge, 2009). These characteristics push the magma through the earth surface on the brittle areas; they form splits known as dykes. Pre-existing fault lines can also work in this process. After magma has erupted, it cools at different paces depending on the temperatures. This type of igneous rock is granular in structure and the crystals can be easily seen (Morgan, 2010). This form of physical appearance is a result of how the crystals arrange during cooling.


a) Conglomerate

This is an ordinary sedimentary rock, which form in dissimilar environments and weather conditions limited to the availability of adequate energy to move huge grains. The sediment that rock is formed from is regularly coarser compared to other sedimentary rock with exception of breccias. The grains of this rock are rounded and normally indicate that they have been carried more than angular grains thus differentiating them from other sedimentary rocks.

b) Limestone

In fact, limestone is a form of sedimentary rock made up of calcium carbonate in form of calcite. This is basically an organic rock formed in shallow, warm and clear marine environs. In such environment, organisms extract ingredients necessary for the formation of calcium carbonate fro marine water. Marine contains skeletal debris of dead animals thus a source of minerals that accumulate to form limestone. However, some limestone may form from the process of precipitation whereby high temperatures cause rapid flow of calcium carbonate from marine water.

c) Gneiss

This is a widespread from of surface rock or rather metamorphic rock. This rock has veins of minerals al through and its main constituents are mica and quartz. It is formed in environments such as high temperatures regions and areas experiencing considerable pressure to emit heat capable of melting rocks. Precisely, rocks under pressure are faulted and end up shearing resulting angular, fine-grained rock sediments. As a result gneiss rock is formed.

d) Marble

This is a form of metamorphic rock usually formed from limestone and is mainly made up of dolomite or a combination of various carbonate minerals. It is formed in areas under great heat and pressure beneath the earth’s crust. The process involves recrystallization. It involves rearrangement of fossilized materials such as grains of calcite, carbonate minerals (Suzanne, 2007).

e) Basalt

This is a variety of igneous rock, which ids quite dark in appearance. It mainly constitutes the ocean floor. It comprise of minerals such as, olivine and pyroxene. Basalt forms in areas that experience frequent volcanic eruption pouring lava on the earth’s surface. The cooling of the lava flow in a couple of days results in a solid rock, basalt (Suzanne, 2007).

f) Obsidian

This is an igneous rock that is formed from molten magma after an extrusive volcanic activity. It lacks minerals crystals. It forms in areas where geological process result in volcanic eruptions and the chemical composition of minerals are appreciably rich in silica. After an eruption the lava flows slowly on the earth’s surface in a viscous manner to form obsidian rock.


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