unit 2 rocks & minerals

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1. Igneous Rocks

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There are many kinds of rock in Earth’s crust

These rocks are made up of different minerals

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Rocks can be grouped by the way they form throughout the

rock cycle

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Igneous rocks form from melted, liquid rock

Vocabulary

Igneous rocks

Rock formed when hard liquid rock cools and hardens

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This process may take place inside Earth

or on Earth’s surface

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Inside Earth, magma cools so slowly that it may take a

thousand years for a rock to form

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One of the most common kinds of igneous rocks is granite

Granite is made by magma cooling inside Earth

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Granite is light colored with large crystals

It is made up mostly of the minerals quartz and feldspar

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Granite is strong and does not break easily, even under

pressure

It is often used in buildings and bridges

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Basalt is made when lava pours onto the ground or onto the

ocean floor

Because the lava cools quickly, the crystals in basalt are small

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When lava erupts underwater it makes pillow-shaped lumps,

called pillow lava

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Sometimes, lava cools so quickly that crystals never

have a chance to form

Pumice and obsidian are igneous rocks that do not have

crystals

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Pumice is full of bubbles and is so light that it floats

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Obsidian is a glassy, black rock

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