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Basalt Rock

Last updated date: 15th Apr 2024
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What is a Basalt?

Basalt is an extrusive igneous or volcanic rock that has a low silica content, dark in colour, and is very rich in iron and magnesium. Basalt rock is mainly composed of pyroxene, olivine, and plagioclase and is the most common rock on the earth's surface. The texture of basalt rocks is coarsely porous as those holes are left by gas bubbles. The specimens of these rocks are mostly fine-grained, glassy and compact. A large part of the ocean floors is made from basalt rocks. When erupted by volcanoes in ocean basins, it can lead to the formation of volcanic Islands. Basalt rocks have also built up huge plateaus on the surface of the land. Maria, the dark plains on the Moon and also volcanoes of Mars and Venus are known to be possibly made up of basalt. 

A basalt dark in colour 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

Basalt rocks are usually formed when the volcanic basaltic Lava rapidly cools from the deep interior of the earth's crust equivalent to plutonic gabbro-norite magma and gets exposed to the Earth surface. Gas cavities are absent in the basalt lows and these floors are generally quite thick and extensive. 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, 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.

  • 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-a 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.  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.


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 per cent of basalt is made of silica.

Basalt rocks are mainly composed of pyroxene olivine and plagioclase, these rocks are rich in Magnesium and iron. The most porphyritic minerals in basalt rocks are augite and olivine. Basaltic lavas are pumiceous and spongy.

These stocks can be categorized into two parts in terms of petrographic basis

  • Alkali basalts- that contain olivine.

  • Tholetiic basalts are basalts without olivine.

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 amphitheatres. 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 fibre/fibreglass. Therefore, melted composites of the basalt rock are employed for manufacturing pipes and rebars that are used in the construction of wind turbine blades.

Other Uses

Basalt rocks are used for construction purposes of buildings, blocks or are also used in the groundwork. These rocks are also used for making statues. Basalt rocks can inhibit crack propagation and also reinforce the concrete from a microscopic perspective. Basalt rocks are used for the toughness of concrete. With its high elastic modulus, it acts as a bridge at the cracks. Extruding and heating of these rocks get converted into stone wool which is potentially an excellent thermal insulator. Basalt rocks were also used for asphalt pavement, road base, railroad blast, and many other purposes.

Fun Fact

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

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

FAQs on Basalt Rock

1. State Various Uses of Rocks.

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

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

2. State Property of Basalt Rock.

Basalt is the most commonly found rock on the Earth’s surface. Its specimens are black in colour and whether 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%.

3. What type of rock is basalt?

Basalt rocks are generally hard black Volcanic rocks which is the most common rock found on the Earth's crust. Basalt rocks can either be hard and massive or full of bubbles and crumbly. Basalt rocks are also used for construction purposes as the fibres of these rocks can easily be mixed with concrete and increase speed post cracking energy absorption.

4. Does basalt absorb water?

Natural stones are generally porous to some extent. Due to exposure, they may absorb some amount of liquid and moisture. Basalt rocks are considered to be dense as compared to other natural stones especially when compared to sandstone but can absorb unwanted contaminants. 

5. What is the importance of sealing basalt tiles?

Application of a good sealant can prevent moisture from getting into the stones which most of the time can alter the appearance of tiles. Without the application of a good sealant, basalt rocks can be affected by permanent discolouration. Although this can be prevented with the penetrating or topical sealant. A topical sealant can protect the surface from various types of damage such as scratches, everyday dust etc.

6. Why are igneous rocks used in construction?

Igneous rocks are used in construction because they can withstand both erosion and weathering as compared to sedimentary rocks. These rocks are used as a plinth at the base. Igneous rocks give strong and hard Foundation construction of reservoirs and dams. Igneous rocks are durable and dense and are also used in making tools.  Granite is the most common igneous rock and is used extensively in making statues and building materials.