What is the Difference Between Basalt and Granite

Basalt and granite are two types of igneous rocks. Both are classified as silicate rocks and contain common minerals like feldspar. However, there is a distinct difference between basalt and granite.

What is the difference between basalt and granite? Basalt has 53% silicon dioxide (SiO_2), while granite has 73% of silicon dioxide.

Key Areas Covered

1. What is Basalt 
      – Definition, Features
2. What is Granite
      – Definition, Features
3. Similarities Between Basalt and Granite
      – Outline of Common Features
4. Difference Between Basalt and Granite
      – Comparison of Key Differences
5. FAQ: Basalt and Granite
      – Answers to Frequently Asked Questions

Key Terms

Basalt, Granite, Igneous Rock

What is Basalt

Basalt is a dark, fine-grained, extrusive igneous rock that has a composition similar to gabbro. The difference between basalt and gabbro is that basalt is a fine-grained rock, while gabbro is a coarse-grained rock. It is formed when molten rock containing magnesium and iron erupts from volcanoes and cools rapidly on reaching the surface. This quick cooldown prevents large crystals from forming, giving basalt its characteristic fine-grained texture. Apart from the Earth, it can also be found on other celestial bodies like the moon and Mars. Most areas of the Earth’s ocean basins are formed by basalt. In the moon, much of the surface area is underlain by flood basalts and basaltic lava flows. Such areas on the moon are called lunar maria.

Basalt has high strength and heat-resistant properties. Its fire-resistant properties are due to its volcanic origins. Crushed basalt is used in the making of roads and at the base of buildings. Basalt fibers are also used as an alternative to asbestos. Geologists study the structure, formation and properties of basalt in order to discover information on volcanic activity and the origin of the Earth.

What is Granite

Granite is a coarse-grained igneous rock rich in history and applications. It is formed deep underground. Granite originates from molten rock (magma) that cools and crystallises slowly. This slow cooling allows for the formation of visible mineral grains, primarily quartz, and feldspar, giving granite its characteristic speckled appearance.

Granite gets its colour from other minerals like mica and amphiboles. The colour of granite may vary from pink and grey to even black. It is strong and durable. These properties make it very usable in the construction field. It is used in creating countertops, floor tiles, and monuments due to its resistance to weathering and wear and tear.

Apart from its uses in the construction industry, it is also used to study Earth’s history. Because it forms deep within the Earth’s crust, granite’s presence often signifies the core of continents. Studying these ancient rocks helps geologists unravel the story of our planet’s formation and evolution.

Similarities Between Basalt and Granite

1. Both granite and basalt are igneous rocks.
2. Basalt and granite contain common minerals like feldspar.
3. Basalt and granite are classified as silicate rocks.
4. Geologists use these rocks to study the nature and history of Earth.

Difference Between Basalt and Granite

Definition

• Basalt is a dark, fine-grained, extrusive igneous rock that has a composition similar to gabbro, while granite is a very hard, granular, crystalline, igneous rock that consists mainly of quartz, mica, and feldspar.

Formation

• Basalt forms when lava erupts from volcanoes and cools rapidly on the Earth’s surface. This rapid cooling results in fine-grained crystals. Granite forms from magma that cools and solidifies slowly beneath the Earth’s surface. This slow cooling allows for the formation of large, visible crystals in the rock.

Appearance

• Moreover, basalt is typically dark gray to black in color due to its higher iron and magnesium content, whereas granite has a wider color range, including light gray, pink, red, or even blue, depending on the mineral composition.

Silicon Dioxide Content

• Basalt has 53% silicon dioxide, while granite has 73% of silicon dioxide.

Type of Rock

• Basalt is considered a mafic rock, meaning it has a higher iron and magnesium content compared to lighter elements like silicon. However, granite is classified as a felsic rock, indicating a higher proportion of silicon and lighter elements compared to iron and magnesium.

Found in

• Basalt is found on ocean floors and volcanic areas, whereas granite is found on continental crust.

Conclusion

In conclusion, basalt and granite are both igneous rocks with distinct characteristics and origins. Basalt, formed from rapid-cooling lava, is dense and dark, found in volcanic regions and ocean floors. Granite, the result of slow-cooling magma, boasts visible mineral grains and a wider color range, often located in continental crusts. Despite their differences, both rocks hold significance in construction and geological studies.

FAQ: Basalt and Granite

1. Which is stronger, granite or basalt?

Granite and basalt are both hard igneous rocks but granite is generally harder than basalt because of its mineral composition and the way it forms.

2. Is basalt lighter than granite?

Basalt has a density of around 3.0 – 3.3 grams per cubic centimeter, while granite has a density of 2.6 – 2.8 grams per cubic centimeter. Hence, basalt is heavier and denser than granite.

3. Does basalt form faster than granite?

Basalt is a volcanic or extrusive igneous rock. Granite, on the other hand, is a plutonic or intrusive igneous rock. This means, basalt forms when lava erupts from volcanoes and cools rapidly on the Earth’s surface while granite forms from magma that cools and solidifies slowly beneath the Earth’s surface.

4. Why is basalt heavier than granite?

Basalt is heavier than granite because mafic magmas, from which basalt forms, contain higher amounts of denser minerals such as pyroxenes and olivine. In contrast, felsic magmas, which produce granite, have a higher content of lighter minerals such as quartz and feldspar.

5. Why is basalt so expensive?

Basalt is a very strong and hard igneous rock.  Hence, it can be difficult to cut and shape. It is this property that makes it an expensive rock in the industry.

Reference:

1. “Basalt.” Encyclopedia Britannica.
2. “Granite.” Encyclopedia Britannica.

Image Courtesy:

1. “Granito nicol incrociati”  By Chiara Groppo – Atlante di petrografia (CC BY-SA 2.5) via Commons Wikimedia
2. “Mineralogy igneous rocks EN” By Woudloper – Own work (Public Domain) via Commons Wikimedia