What is the Difference Between Basalt and Rhyolite

The main difference between basalt and rhyolite is that basalt usually appears in dark colours, while rhyolite usually appears in light colours.

Both rhyolite and basalt are types of igneous rocks. Igneous rocks are usually found in two forms as intrusive and extrusive igneous rocks, based on the method of formation. Basalt is an extrusive igneous rock type. Rhyolite is considered as an extrusive volcanic rock that is equivalent to granite.

Key Areas Covered

1. What is Basalt
     – Definition, Features, Formation
2. What is Rhyolite
     – Definition, Features, Formation
3. What is the Difference Between Basalt and Rhyolite
     – Comparison of Key Differences

Key Terms

Basalt, Igneous Rock, Rhyolite

What is Basalt

Basalt is a type of an extrusive igneous rock that forms at or near the surface of a planet’s crust. These rocks found not only in Earth but also in other planets such as Mars or moon. Moreover, these rocks form from the rapid cooling of magnesium and iron-rich lava. Almost 90% of volcanic rocks on Earth’s crust are basalt rocks.

Figure 1: Basalt

Due to the presence of low silica content, basalt lava has a low viscosity. This can cause rapid lava spreading over a great area before it gets cooled and solidified. In general, basalt is fine-grained material with very low amounts of silica and feldspar. Typically, we can observe this rock appear in grey or black colour. It can also easily undergo weathering into brown coloured basalt due to the oxidation of its mafic minerals.

The term basalt is important mainly to describe the extrusive rocks. There are different types of basalt, including tholeiitic basalt, high-alumina basalt, alkali basalt, boninite or high magnesium basalt, lunar basalt, etc.

What is Rhyolite

Rhyolite is a type of igneous rock that is extrusive. Typically, these rocks are light-coloured rocks. They have a small crystalline structure and gets cooled quickly. Moreover, we can categorize these rocks as felsic because these rocks are rich in silica. We can observe the occurrence of these rocks at the continental crust. Apart from that, these rocks are comparatively less dense.

Figure 2: Rhyolite

Rhyolite is considered as the extrusive equivalence to that of granite (a plutonic rock type). This type of rock has a high silica content and a low iron and magnesium content. Therefore, the magma of rhyolite forms highly viscous lava. We can observe the occurrence of these rocks at dikes and volcanic plugs. Some forms of rhyolite cool quickly. These rocks form obsidian (a natural glass) from quick cooling. Some rhyolite type rocks cool slowly. Moreover, the eruption of rhyolite lava is very rare.

Difference Between Basalt and Rhyolite

Definition

Basalt is a type of an extrusive igneous rock that forms at or near the surface of a Planet’s crust while rhyolite is a type of igneous rock that is extrusive.

Appearance

While basalt is dark coloured, rhyolite is light-coloured.

Silica Composition

Basalt has a low silica and feldspar content while rhyolite is rich in silica and feldspar

Iron and Magnesium Composition

Furthermore, basalt is low in iron and magnesium, while rhyolite is rich in iron and magnesium.

Conclusion

Both rhyolite and basalt are types of igneous rocks. Moreover, igneous rocks are usually found in two forms as intrusive and extrusive igneous rocks, based on the method of formation. Both rhyolite and basalt are extrusive rocks. The main difference between basalt and rhyolite is that basalt usually appears in dark colours, while rhyolite usually appears in light colours.

Reference:

1. “Basalt.” Wikipedia, Wikimedia Foundation, 19 May 2020, Available here.
2. “Rhyolite.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 20 Jan. 2020, Available here.

1. “BasaltUSGOV” By Unknown author – (Public Domain) via Commons Wikimedia
2. “PinkRhyolite” By Michael C. Rygel – Own work (CC BY-SA 3.0) via Commons Wikimedia