Intrusive Igneous Rock

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Intrusive igneous rocks are formed by the intrusion of magma into older rocks deep inside the Earth’s crust, which then solidifies slowly within the crust.

Intrusive rocks are coarse-grained such that the interlocking mineral crystals can be easily identified with the naked eye. They can be classified based on the size and shape of the intrusive body.

As the magma within the rocks starts cooling, elements tend to combine and form silicate minerals which are the building blocks of igneous rocks. These mineral crystals can grow large if there is enough space. Typical intrusive formations include dikes, sills, laccoliths, stocks and batholiths. Some of the coarse-textured intrusive rocks include diorite, gabbro and granite.

Intrusive igneous rocks such as granite are present in the central cores of major mountain ranges. These cores, however, may cover large areas of Earth’s surface when exposed by erosion. Intrusive rocks that form near the surface are known as hypabyssal, while the coarse-grained intrusive rocks at depth of the crust are known as abyssal.

References

• Igneous Rocks – Geology.com
• Intrusive igneous rocks – California State University
• Intrusive Rocks – Georgia State University