Difference Between Dyke and Sill (With Table)

A number of slight, as well as drastic changes and activities, keep happening below the surface of the Earth. These changes are sometimes experienced above the ground, while sometimes they don’t. Similarly, Dykes and Sills are an accumulation of volcanic or igneous rocks that are forced to penetrate other stones and surfaces due to high pressure and temperatures. These rocks are slimmer than the other rocks that surround them.

Dyke vs Sill

The difference between Dyke and Sills is that Dykes are volcanic rocks that grow vertically, whereas Sills are igneous rocks that grow in the horizontal direction. Dykes and Sills are both are the end result of magma crystallization that is present beneath the surface of Earth.

Dykes are formed by the crystallization of molten magma and are, therefore, a type of igneous rock. They intrude in between other bedding rocks and grow vertically. The origin point of Dukes is below them. Due to their vertical growth, they can be easily identified and set apart from others.

Sills are also a result of the crystallization of molten magma below the Earth’s surface. They are different from Dykes in a number of ways like they grow in a horizontal direction and have their origin point on the left or right side of it. Since they grow horizontally, it’s hard to identify them.

Comparison Table Between Dyke and Sill

Parameters of ComparisonDykeSill
Direction of growthDykes grow verticallySills grow horizontally
Ease of distinguishingDykes are usually easier to distinguishSills are harder to distinguish
Point of originTheir point of origin is beneath themTheir point of origin can be on either left or right side
Way of intrusionDykes intrude in between the bedding rockSills intrude horizontally
Intrusion typeThese are called Discordant intrusionsThese are called Concordant intrusions

What is Dyke?

Volcanic eruptions result in a lot of molten magma flowing all around the volcano and even deep down in the grounds. Dykes are volcanic or, more commonly known as igneous rocks that are formed as a result of crystallization of the molten magma under the surface of the Earth. Their nature is to grow vertically and is therefore also classified in the same manner, which is vertical, nearly vertical, and steep.

There is another classification of Dykes, and by that, they are categorized as basaltic to granitic, diabase, and rhyolitic. Dykes protrude the bedding rocks from between. This process is also sometimes done artificially by introducing them into the rocks, and then they grow naturally. The intrusion type of Dykes is known as Discordant intrusion.

Like anything else, even Dykes have a point of origin. This origin point is generally under the Dykes. And so, when they need to be infused artificially, this characteristic of point of origin is kept in mind. One more advantage of the vertical growth of Dykes is that they can easily be identified and distinguished from other types of rocks. No extensive testing or investigation is required to differentiate or identify them, which is an excellent easy.

What is Sill?

Nature evolve and transform into a variety of thing from a single origin. Just like that, the molten magma from volcanic eruptions forms one more type of rock, which is known as Sills. These are also included in a similar manner as Dykes that is by crystallization of molten magma beneath the surface level of Earth. 

Sills grow differently that Dykes. They grow in a horizontal direction with respect to the original rock. These are made up of rocks that are medium-grained and often have a uniform orientation. In this, the surrounding rocks help it, but Sills can also be non-uniform at times. 

Sills protrude their surrounding rocks in a parallel fashion. The intrusion type of Sills is called concordant because they grow parallel with respect to the origin land or rocks. Interestingly, The origin point of Sills is not below them./ But instead, their point of origin is either on the left or right side of them. Their horizontal growth also gives rise to a complexity which is that they become hard to identify and differentiate from other surrounding rocks. And therefore, extensive testing and research are required to make sure which is a Sill type rock.

Main Differences Between Dyke and Sill 

  1. Dykes are igneous types of rocks that grow vertically, while Sills are igneous types of rock that grow horizontally.
  2. Dykes are known to be discordant intrusions, whereas Sills are known to be concordant intrusions.
  3. Dykes have intrusions in between the bedding rocks. On the other hand, sills have intrusions parallel to rocks and planes.
  4. Dykes are created when the origin point of the forming dyke is beneath, while Sills are formed with their origin point on the right or left side.
  5. Dykes are easier to identify, whereas Sills are difficult to distinguish. The reason for this is the direction of their growth.


The molten magma erupted from the hot volcanoes, made its way much deeper into the Earth’s surface, and then crystallized. These crystallized form of molten magma is of two types called Dykes and Sills. They are thinner than the rocks they cut into. They are different in a lot of factors like Dykes have their origin point below while Sills have it on either side that is left or right.

Also, Dykes protrude a rock from in between while Sills protrude parallel to the bedding rocks. They can even be injected artificially into a rock to form the origin and then left to grow on their own. There are also many other types of igneous rocks that are in some ways similar as well as dissimilar from Dykes and Sills.


  1. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2009JB006791
  2. https://www.sciencedirect.com/science/article/pii/001623619090016J

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