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A World of Rocks:
What is a rock? Is it something you skip in a river? Is it something you kick along a sidewalk? Is it something you climb on just for fun?
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A rock is all this and a whole lot more.
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Earth is mostly made up of rocks. Water, soil, plants, and roads cover Earth's surface. If you dug far enough down, you'd hit solid rock.
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Even towering mountains
are really rocks!
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Colorful Minerals:
Look closely at a slab of granite. Do you see how it is speckled gray, pink, and green? Each of those colors comes from a different mineral.
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Minerals form in the earth. They are the ingredients that make up rocks.
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Three Types of Rocks:
There are three groups of rocks:
igneous, sedimentary, and metamorphic.
These rocks form in different ways.
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Igneous Rocks
Imagine you could dig a hole deep into Earth.
You'd find places so hot that even rocks had melted.
The melted rock is called magma. This hot, gooey
liquid turns into igneous rocks.
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The magma rises through cracks inside the earth.
As the magma cools, it hardens. Sometimes it
becomes hard rock while it is still underground.
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Sometimes magma shoots out of a volcano as lava.
The lava flows across the ground like a red-hot river. Soon it cools into new rocks.
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Sedimentary Rocks:
Sedimentary rocks take shape on top of the earth, not inside it.
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Wind, water, and ice whip against large rocks.
Little by little, the rocks break into
tiny pieces. These bits of rock
are called sediment.
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The sediment piles up on the
ground or at the bottom of seas
and rivers. More rocks break
away. The layers of sediment
build up.
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The top layers press on the bottom layers.
This glues the sediment together.
After millions of years, the bits of rock
have grown into one very large rock.
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Metamorphic Rocks:
Old rocks can become new rocks when they get trapped under the ground. Heat inside
the earth can change which minerals make up rocks. Or rocks can get squeezed or folded as the earth moves.
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Either way, the new rocks are called metamorphic rocks.
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Useful Rocks:
All these rocks help people in many ways. Artists carve statues out of smooth marble. Crushed limestone makes cement for sidewalks. Diamonds and rubies are rocks that sparkle in beautiful jewelry.
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Look all around. Where do you see
rocks in nature? How have people
used rocks? You might be surprised
to find just how many rocks there are!
