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Igneous rocks are one of the three main types of rocks, along with sedimentary and metamorphic rocks. They form when molten rock, called magma, cools and solidifies. This process can happen deep underground or on the Earth’s surface.
Magma is created when rocks inside the Earth melt due to high temperatures and pressure. As magma rises toward the surface, it can cool slowly beneath the ground. This slow cooling allows large crystals to form, resulting in coarse-grained rocks like granite. These are called intrusive igneous rocks because they form inside the Earth’s crust.
Sometimes, magma erupts from volcanoes as lava. When lava reaches the surface, it cools quickly. Rapid cooling prevents large crystals from forming, creating fine-grained or glassy rocks like basalt or obsidian. These are called extrusive igneous rocks because they form outside the Earth’s crust.
The type of igneous rock depends on the magma’s composition. Magma rich in silica produces light-colored rocks, such as rhyolite. Low-silica magma forms dark rocks, like basalt. Gas bubbles trapped in lava can also create porous rocks, such as pumice.
Igneous rocks are important because they make up much of the Earth’s crust. They also provide clues about the planet’s history and volcanic activity. By studying them, scientists learn about the conditions deep inside the Earth.
In summary, igneous rocks form from cooled magma or lava. Their texture and composition depend on where and how quickly they cool. Whether they are intrusive or extrusive, these rocks help us understand the powerful forces that shape our planet.
What is the main idea of the passage?
The differences between sedimentary and metamorphic rocksHow igneous rocks form from magma or lavaThe history of volcanic eruptions on EarthWhy igneous rocks are the hardest type of rockWhere do intrusive igneous rocks form?
On the Earth’s surfaceInside the Earth’s crustIn ocean waterInside active volcanoesWhat determines the grain size of igneous rocks?
The color of the magmaThe speed at which the magma coolsThe amount of gas in the lavaThe age of the rockWhich rock is an example of an extrusive igneous rock?
GraniteBasaltMarbleSandstoneWhat does magma rich in silica produce?
Dark-colored rocksLight-colored rocksPorous rocksMetallic rocksWhat is the meaning of "extrusive" in the passage?
Rocks that form inside the EarthRocks that form from cooled lava on the surfaceRocks that change under heat and pressureRocks made from compressed sedimentsWhy are igneous rocks important for scientists?
They are the rarest type of rockThey provide clues about Earth’s history and volcanic activityThey are used to make jewelryThey float in waterWhat happens when lava cools very quickly?
It forms large crystalsIt becomes sedimentary rockIt forms fine-grained or glassy rocksIt turns back into magma
