Basic Rock Types

Understanding basic rock types gives you more ideas on how each type of rock is formed and this is a good basic for understanding geology.

Rocks can be classified into three main types which are igneous rocks, sedimentary rocks and metamorphic rocks. Figure 1 shows the relationship between the three main rock types.


Figure 1 – Rock Cycle

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Igneous Rocks

Igneous rocks are the most abundant type of rock on the Earth because it makes up about 70% of all rocks. Minerals such as quartz, plagioclase feldspar, pyroxene and olivine are important types of igneous rocks. Figure 3 illustrates minerals found in common igneous rocks.

Figure 2  – Minerals in Common Igneous Rocks.

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Plate Margins in Oil and Gas Industry

After learning about the Earth’s structure and Plate Tectonics, it is known that the Earth’s plates move relative to nearby plates; therefore this will result in high geological activities such as volcanic eruptions and earthquakes at the plate margins. It is also possible to have geological activities in the middle of plates, but it is quite uncommon. There are three type of plate margins; convergent, divergent and transform.

Divergent Margins

This happens when the Earth’s plates are moving apart and a new lithosphere is created (Figure 1).  In the oceans, the divergent process has produced the mid-ocean ridge system, which can also be described as a global range of underwater mountains. There are several ocean ridges such as the Juan de Fuca Ridge, the Mid-Atlantic Ridge, the Galapagos Rise and the East Pacific Rise. On land, the divergent margins create rift valleys such as the Red Sea and East African Rifts (Figure 2).

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Earth Structure and Plate Tectonic

The basic concept of the Earth structure and Plate Tectonic is good to know for drilling oil and gas wells.

The image below (Figure 1) shows the Earth structure. There are tree compositional layers which are curst, mantel and core. At the center of the Earth, the center core is a solid iron core which is surrounded by a liquid iron core. Core has a range between 2,900 – 6,370 km from surface. Mantel which has its range between 100 – 2,900 km consists of upper and lower mantel. Lower mantle (Meshosphere) is hot but strong due to high pressure however upper mantle is weak, hot and molten. Crust is a surface of the Earth and a majority of the Earth crust is made up of iron, silicon, oxygen and magnesium.

Figure 1 – Earth Structure

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