Question

What are the two most common kinds of igneous rock?

Short answer

The two most common igneous rocks are granite and basalt.

Step-by-step solution

Understand the Question

Before solving the exercise, we need to understand that we are asked about the two most common types of igneous rocks.

Define Igneous Rocks

Igneous rocks are formed from the solidification and cooling of magma or lava and are often categorized by where they form, either beneath the surface (intrusive) or at the surface (extrusive).

Research the Common Types

To determine the most common types, we need to look into geological studies and sources, which state that the two most common igneous rocks are granite and basalt.

Explain Granite and Basalt

Granite is an intrusive igneous rock, meaning it forms beneath the Earth's surface, and is typically coarse-grained. Basalt is an extrusive igneous rock, forming at the Earth's surface, and is fine-grained.

Verify Knowledge

Ensure the information about granite and basalt as common igneous rocks is accurate by consulting reliable geological texts or educational resources.

Key concepts

Granite

Granite is one of the most well-known types of igneous rock because it is widely used in architecture and construction. It is an intrusive igneous rock, which means it forms beneath the Earth's surface. This formation process gives granite some distinct properties.

• It is generally coarse-grained, allowing us to see its mineral components like quartz, feldspar, and mica, which are large and visible.
• Granite is very hard and durable, making it ideal for countertops, flooring, and monuments.
• It comes in a variety of colors, from pink to gray, depending on its mineral composition.
  

Granite's formation requires slow cooling of magma deep within the Earth, often over thousands or millions of years, resulting in its large, interlocking crystals. This slow cooling occurs because the magma is insulated by surrounding rock layers, allowing for extended crystallization.

Basalt

Basalt is another key type of igneous rock, known for its fine-grained texture and dark appearance. Unlike granite, basalt forms at the Earth's surface and is an extrusive igneous rock.

• It forms from rapidly cooling lava, which results in its fine-grained structure.
• Basalt is generally composed of minerals like pyroxene, olivine, and plagioclase, with little or no quartz.
• Because of its dense nature, basalt is heavy and has applications in construction, such as road base and railway ballast.

Most of the ocean floor is made up of basalt, as it is the primary rock formed by volcanic activity along mid-ocean ridges. Therefore, basalt is more common than granite but might be less visible to us on the surface.

Intrusive and Extrusive Formations

Intrusive and extrusive formations are ways to classify igneous rocks based on where they form relative to the Earth's surface. This distinction is fundamental in geology and helps explain the differences between rock types like granite and basalt. Intrusive formations occur when magma cools and solidifies beneath the Earth's surface. Because the cooling process is slow, these rocks, like granite, have large crystals and coarse-grained textures. These formations are not typically visible until erosion or human activities uncover them.

Extrusive formations, on the other hand, happen when lava cools quickly at the Earth's surface. Rapid cooling results in fine-grained or even glassy textures, such as those found in basalt. This process can happen during volcanic eruptions, where lava flows and solidifies rapidly. Understanding the difference between intrusive and extrusive rocks helps in studying Earth's geology and understanding rock cycle processes. It also aids in determining the geological history of an area, providing insight into past volcanic activity and tectonic movements.