Back
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

igneous rock

Primary Information
Secondary Information

Definition

Igneous rocks are rocks that form from the cooling and hardening of magma or lava. Magma is hot, molten rock that is found underground. Lava is magma that has erupted from a volcano and flows onto the surface of the Earth.

Igneous rocks are classified into three main types based on where they form:

  • Extrusive igneous rocks form when lava cools and hardens on the surface of the Earth. They are typically light-coloured and have a lot of holes in them. This is because the lava cools quickly on the surface and doesn't have time to form crystals.
  • Intrusive igneous rocks form when magma cools and hardens underground. They are typically dark-coloured and have a solid structure. This is because the magma cools slowly underground and has time to form crystals.
  • Pyroclastic rocks form when bits of hot, molten rock and ash are thrown into the air by a volcano and then fall back to the ground. They are typically light-coloured and have a lot of sharp edges. This is because the ash and rock cool quickly when they hit the ground and don't have time to form crystals.

Igneous rocks are important because they make up much of the Earth's crust. They also provide us with valuable resources, such as granite, basalt, and diamonds.

How can the word be used?

Igneous rocks can be used to make building materials, such as granite and basalt.

igneous rock

Different forms of the word

There is no other form of the word "igneous rock". It is a noun that refers to a type of rock that formed from the cooling and solidification of molten rock (magma or lava).

Etymology

The word "igneous" comes from the Latin word "igneus", which means "fiery" or "of fire". This is a very accurate description of igneous rocks, as they are formed from molten rock that is very hot.

Question

What is igneous rock?

AQA Science Exam Question and Answer

Question:

Explain the formation and characteristics of igneous rocks, detailing the processes of cooling and crystallization of molten magma, and discuss how the classification of igneous rocks is based on their mineral composition and texture.

Answer:

Igneous rocks are formed through the solidification of molten magma, which originates from within the Earth's mantle or crust. When magma is exposed to lower temperatures at or near the surface, it cools and undergoes crystallization, transforming into solid rock.

The cooling rate of magma determines the size of crystals formed in the rock. Rapid cooling, as seen with volcanic eruptions, results in smaller crystals, creating a fine-grained texture. Slower cooling, which occurs when magma solidifies deep within the Earth, leads to larger crystals and a coarse-grained texture.

Igneous rocks are classified based on their mineral composition and texture. Rocks rich in silica tend to be lighter in colour and are classified as felsic, while those with lower silica content are darker and categorised as mafic. The texture, whether fine-grained or coarse-grained, also aids in classification.

For instance, granite, a common igneous rock, is felsic and coarse-grained due to its slow cooling history. Basalt, on the other hand, is mafic and fine-grained because it cools rapidly at the surface during volcanic activity.

In summary, igneous rocks are formed from solidified magma and exhibit a wide range of characteristics based on cooling rates, mineral composition, and texture. Their classification provides insights into their origin and geological history, offering valuable information about Earth's processes and history.