Igneous Rocks

While you may know them better as volcanic rocks, igneous rocks form when magma or lava cools and crystallizes. Igneous rocks are appropriately named. The word "ignite" and the word "igneous" both come from the Latin word "ignis," which means fire. These rocks truly have a fiery beginning. Melted rock is identified as both magma and lava because it exists in two locations. Magma is used to identify all melted rock found beneath the Earth's surface and lava is all melted rock that erupts and flows on the surface of the Earth.

Crystallization

There are two types of igneous rock: intrusive and extrusive. Both of these types of igneous rocks are the result of crystallization. Extrusive igneous rocks form from lava on the surface. Intrusive rocks form beneath the surface from magma. During the process of crystallization, the minerals within the rocks can either form quickly or slowly. The rate of crystallization determines the properties of the igneous rock. View this presentation to learn more about the crystallization process and differences between the two types of igneous rocks. Click the player button to begin.

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Igneous Intrusions

You have learned that magma does not always make it to the surface to erupt from volcanoes as lava. The Earth's interior is characterized by very high temperatures and pressures. At these extreme pressures, it is common for huge volumes of magma to be squeezed towards the surface of the Earth. When the magma erupts to the surface, a volcano is formed. However, the magma does not always erupt through the surface. In these cases, an igneous intrusion is created. An igneous intrusion is a mass of igneous rock that forms underground when magma is injected into preexisting rock. The magma cools slowly over time to produce igneous rock with a coarse-grained texture. This rock can become exposed at the Earth's surface after many years of erosion.

Textures

Igneous rock texture is the arrangement of the minerals within a rock. There are four igneous rock textures with which you should be familiar to help you distinguish igneous rocks from other rock varieties. In this activity, learn about the different textures found within igneous rocks. Click the player button to begin.

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The Types of Magma and Lava

There are three types of magma and lava that are different based on their chemical composition. The composition will determine the colors of the rocks that crystallize. This makes it easier to correctly identify different rock types without using complicated laboratory equipment. You can simply analyze the composition of a rock by identifying the colors of the minerals present. While each magma or lava is composed of hundreds of different elements, you will focus on the most dominant elements for each of the three types. Please view the characteristics of the three types of magma or lava in the table below.

Magma/Lava Type	Dominant Elements	Resulting Mineral Colors
Felsic (Granitic)	Silicon and Oxygen	Light Colored Rocks (white, light gray, clear, pink)
Mafic (Basaltic)	Iron and Magnesium	Dark Colored Rocks (black, green, maroon)
Intermediate (Andesitic)	Silicon, Oxygen, Iron, and Magnesium	Intermediate Colored Rocks (a mix of colors)

Common Igneous Rocks

Now that you have learned how igneous rocks form, the types of igneous rocks, the textures of igneous rocks, and the types of magma, it is time to investigate some examples. These rocks have plenty of uses. Granite rock is commonly used in construction, while pumice can be used in certain soaps. In the interactivity, you will learn more about each of the common igneous rocks. Click the player button to begin.

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Igneous Rocks Review

Now that you have explored igneous rocks, how they form, and the many common examples, it is time to review your knowledge. In this non-graded interactivity, read each question, then select the appropriate answer. Click the player button to get started.