Produced in collaboration with the National Science Foundation.
Rocks are all around us. They are under the foundations of our houses; they form the mountains we hike and they shine brightly in our jewelry.
What Exactly Is a Rock? How Do Scientists Study Rocks and Tell Them Apart?
Rocks are made of minerals. A mineral is a nonliving substance made of crystals. Crystals are ordered arrangements of molecules, like bricks in a wall. We can tell the difference between different types of rocks by looking at the minerals they are made of, how much of each mineral there is, and how they are arranged to form the rock.
You can help your child understand the relationship between rocks and minerals with cereal! Consider two different types of cereal that have multiple parts, like granola with dried fruit or shapes with marshmallows. Each part of a cereal has a distinct color and shape, just like a mineral. If you pour some of each cereal into two separate bowls, you have the equivalent of two rocks — each with its own composition (a "rock" with "minerals" that are granola and fruit, and another "rock" with "minerals" that are shapes and marshmallows). The combination of those parts makes a cereal that has a name, just like a rock!
Scientists can sometimes identify a rock without special tools. They often need to examine very thin slices of rocks with a special type of light and microscopes to get a closer look.
Use the "Science of Rocks" coloring worksheet to find out what a scientist sees when they examine a slice of rock.
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Rocks Form Under Different Conditions
Some form deep beneath the Earth's surface, under high temperature and pressure. Rocks can also form very close to the surface, at the bottom of the ocean, or even in space. Scientists can tell what rocks are made of just by looking at thin slices of rock. The types of minerals found in a rock and the shape of the mineral crystals can tell us what type of rock we are looking at and where and how it formed.
In some cases, rocks from outer space can help us understand the Earth. NSF-funded researchers studied a meteorite that was changed by the high temperatures and pressures as it crashed to Earth. These same conditions are found in the very center of our planet. While we cannot collect samples from Earth's interior, we can use these meteorites to help us understand what goes on deep within our planet.
Use the "What's in a rock?" worksheet to learn about what different types of rocks look like under a microscope, and use your observation skills to identify the rocks.
Be a Rock Detective
The next time you are at the beach, you may be able to spot another type of rock called sandstone. As the name suggests, sandstone is made out of sand, just like the kind you find on the beach itself. Sandstone forms when sand particles accumulate in layers and the spaces between the sand grains are filled in and cemented, forming a solid rock. Beaches like Sunset Cliffs Beach in San Diego have dramatic cliffs made entirely out of sandstone. The cliffs' layers are revealed as ocean waves erode the sandstone over thousands or millions of years. The cliffs can be dangerous, so don't get too close, but be sure to look for the distinctive layers.