Difference Between Intrusive And Extrusive Rocks
Introduction
Geologists classify rocks into different types based on their formation process, composition, and texture. Two major categories of rocks are intrusive and extrusive rocks. These terms refer to the manner in which the rocks have cooled and solidified from molten rock material beneath or on the Earth’s surface. Let us explore the differences between these two types of rocks.
Definition of Intrusive and Extrusive Rocks
Intrusive rocks, also known as plutonic rocks, are formed by the solidification of magma beneath the Earth’s surface. This magma slowly cools and crystallizes over a long period of time, resulting in the formation of large, coarse-grained minerals.
On the other hand, extrusive rocks, also called volcanic rocks, form from lava that cools rapidly on the Earth’s surface or at shallow depths just below the surface. The rapid cooling prevents the growth of large crystals, resulting in the formation of fine-grained minerals.
Texture
The texture of a rock refers to the size, shape, and arrangement of its constituent minerals. Intrusive rocks have a coarse-grained texture due to slow cooling underground. The slower cooling allows larger mineral crystals to form, giving the rock a visible grainy appearance. These minerals are often visible to the naked eye and can be easily identified.
On the contrary, extrusive rocks have a fine-grained texture due to rapid cooling on or near the Earth’s surface. The fast cooling process restricts the growth of minerals, resulting in smaller crystal formation. These rocks have a smooth, glassy or vesicular appearance. The minerals in extrusive rocks are so small that they are generally not easily visible to the naked eye.
Composition
The composition of intrusive and extrusive rocks can vary significantly. Intrusive rocks are typically rich in minerals containing feldspar, quartz, and mica. The slow cooling process allows these minerals to crystallize and separate, giving the rock its distinct composition.
On the other hand, extrusive rocks are mainly composed of basalt, andesite, or rhyolite. These rocks commonly contain minerals such as pyroxene and feldspar. The rapid cooling at the Earth’s surface does not allow enough time for the separation and growth of different minerals, resulting in a more homogeneous composition.
Examples
Some common examples of intrusive rocks include granite, diorite, and gabbro. Granite is composed of quartz, feldspar, and mica. It is widely used in construction due to its durability and aesthetic appeal. Diorite, often found in mountain ranges, is composed of plagioclase feldspar, biotite, and amphibole. Gabbro, which is similar to basalt in composition but with larger mineral grains, is commonly used in construction as well.
Examples of extrusive rocks include basalt, andesite, and obsidian. Basalt, a dark-colored rock, is rich in iron and magnesium minerals. It is found in volcanic areas and is commonly used as a construction material. Andesite, a fine-grained rock, often forms lava domes and volcanic plugs. Obsidian, known as volcanic glass, is formed when lava cools extremely quickly, resulting in a black, shiny rock with no visible mineral grains.
Uses
Intrusive rocks, such as granite and gabbro, are extensively used as building materials, decorative stones, and countertops. Due to their durability, they are also commonly used to construct monuments and statues. The coarse-grained texture and distinct mineral composition make them visually appealing in architectural applications.
Extrusive rocks, such as basalt and andesite, are mainly used for road construction, railway ballast, and concrete aggregate due to their strength and resistance to weathering. They are also used for making high-quality tiles, pavers, and gravestones.
Conclusion
Understanding the difference between intrusive and extrusive rocks is important for geologists and those interested in Earth sciences. The cooling process, texture, composition, and uses of these rocks make each category unique. Intrusive rocks with their coarse-grained texture and variety of mineral compositions are suitable for construction and decorative purposes. In contrast, extrusive rocks with their fine-grained texture are more commonly used as construction material due to their strength and durability. Both categories of rocks play a crucial role in Earth’s geological history and have numerous applications in our daily lives.
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Difference Between Intrusive And Extrusive Rocks
