What is a Basalt?

Basalt is an extrusive igneous or volcanic rock that has a low silica content, dark in color, and very rich in iron and magnesium.

A basalt dark in color can be called the dark basalt. We find its applications in textile industries, fire protection. From these places, we get a clear idea that understanding basalt use is really important for us. 

In this article, we will understand what basalt is, the use of basalt, basalt type, and more about this in detail. 


Basalt is an igneous rock that is formed from the quick cooling of lava rich in magnesium and iron when exposed at or very near the surface of a terrestrial planet or the moon.

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Point to Note:

We must note that more than 90% of all volcanic rock on Earth is basalt, and the eruption/bursting of basalt lava is seen by geologists at around twenty volcanoes every year. 

Basalt is also a crucial volcanic rock type on other planetary bodies in the Solar System. For example, the lunar maria are plains of flood basaltic lava flow and basalt is a common rock existing on the surface of Mars.

Basalt Formation

Now, let’s understand the basalt formation at various locations:

  • Place 1: At oceanic divergent borders

We can find most of Earth’s basalt at the tectonic plate boundaries in the ocean that forms a global ridge system in the middle of the ocean. 

The convection currents in the mantle pass hot molten magma to the Earth’s crust via eruptions on the seabed, and therefore, forming large landscapes of pillow-shaped basalt after cooling down. However, since these activities occur far away from human observation/view, we find that seismic readings are the only way of monitoring such basalt flow.

  • Place 2: Oceanic hotspots

In a similar process, we discussed above, the oceanic hotspots are known to produce huge amounts of basalt. The magma flow at any one spot can burst anytime, and continuous lava flow at such locations may slowly accumulate to become an island. 

Fun Fact:

The Hawaiian Islands that we find in China were all made due to basalt eruptions.

  • Place 3: Continental volcanic activity

Dark basalt  (a basalt type) is formed inland, it mostly comes from large vents and fissures that deposit large amounts of basaltic lava to the surface of the Earth. These eruptions continue for a long period or a time, which ultimately result in vertical stacks or columns.

  • Place 4: Basalt rock cycle

The basalt rock cycle is a process that commences over a time -period of millions of years. All the basaltic magma is pulled out of the mantle to the Earth’s crust because convection currents are continually pushed away from the fissures because of the new magma flow. 

Finally, over a period of many years (millions of years), the older basalt crust slowly sinks back into the magma, ending its cycle where it began or started its formations.

Properties of Basalt

Let’s discuss some physical properties of basalt:

  • Rock Hardness

Rock hardness property is usually measured to determine the compressive fracture strength, to determine whether a rock is a soft rock or a hard rock. T

The rock hardness of basalt is 6 as per the Mohs scale and can be observed through a combination of its compressive strength.

Generally, 100-300 Mpa or Megapascal is the compressive strength.  Its tensile strength is10-30 Mpa, and its shear strength is 20-60 Mpa, which denotes that depending on the mineral makeup, basalt rocks fall in the category of a strong – very strong. 

Rock hardness property is common among the densest, fine-grained textured rocks, such as basalt.

  • Density

The density of basalt is very high, the density of basalt can be seen through the combination of the porosity of the rock, i.e.,  0.1 – 1%, and its bulk density is 2.8 – 3 Mg aka megagram per meter cube; It is because about 50 percent of basalt is made of silica.

Use of Basalt

Uses During Ancient Times

During the ancient period of the Roman Empire, engineers employed basalt for discovering roads, and also to make seats in areas of public performances viz: stadiums and amphitheaters. 

Basalt rocks were also widely employed in mills for grinding purposes. The Rosetta Stone is also formed of basalt.



There are several uses of this rock in construction. For instance, crushed basalt is used in making the base for roads and pavements, as a part of concrete mixtures for constructing railroads, and as filter stones in drainage projects. The rock is also employed in slabs and sheets to create tiles, bricks, and other stone objects for constructing buildings and large monuments.



Many farmers and gardeners employ basalt rock dust fertilizer because it is good for increasing the growth of plants while making it tough for weeds to spread in flowerbeds or other unwanted growing areas.


Industrial Manufacture

The tensile strength of basalt is quite high, it is much greater than carbon fiber/fiberglass. Therefore, melted composites of the basalt rock are employed for manufacturing pipes and rebars that are used in the construction of wind turbine blades. 

We often use Ophitic basalt in the medical industry for orthopedic purposes.

FAQs (Frequently Asked Questions)

Question 1: State Various Uses of Rocks.

Answer: The uses of various types of rocks are as follows:


1. Uses of Andesite Rock

Andesite is an igneous rock that comprises a porphyritic texture. This rock is made of molten magma, which has a low viscosity. 


2. Use of Igneous Rocks

Igneous rocks are generally used in flooring, landscaping, and construction projects. However, igneous rock uses are specific to its type that is classified according to the process of formation, and mineral content.


3. Uses of Silicone oil

A Silicone oil has numerous medical, automotive, and various industrial applications.

Question 2: State Property of Basalt Rock.

Answer: Basalt is the most commonly found rock on the Earth’s surface. Its specimens are black in color and weather dark green or brown. This rock is rich in iron and magnesium and is mainly formed of olivine, pyroxene, and plagioclase. Most of its specimens are compact, fine-grained, and glassy. They can/cannot be porphyritic, phenocrysts of olivine, augite, or plagioclase. Holes left by gas bubbles can give basalt a coarsely/deep porous texture.

It has the following properties:

1. A type of group – volcanic.

2. Colour – dark grey to black.

3. Texture – aphanitic, it can be porphyritic

4. Mineral content – groundmass of a basalt rock generally of pyroxene or augite, plagioclase, and olivine, possibly with minor glass particles. If porphyritic, the phenocrysts can be of olivine, pyroxene, or plagioclase.

5. Silica (SiO₂) content – 45% to 52%.

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