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Rock cycle

We bet you thought that rocks are just rocks, but the truth is there are three different kinds of rocks. Learn the differences between sedimentary, metamorphic and igneous rocks. Created by MIT+K12.

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Video transcript

(printing machine) (rock music) - [Voiceover] I bet you thought rocks are just rocks, right? (record scratching, music stops) Nope. There are three major types of rocks: sedimentary, igneous, and metamorphic. But the coolest thing about rocks is that each one has the ability to change into the other kind. - Huh? - How is that possible? (rock music) (record scratching, music stops) - [Voiceover] Sedimentary, metamorphic, and igneous rocks change into each other in a process we call the rock cycle. (rock music) (music stops) No, not that kind of rock. This kind of rock. (rock music) (music stops) Yeah, that's more like it. The first type of rock we'll talk about is sedimentary. On the surface of the Earth, wind and water break down rock into tiny pieces. Those pieces might collect in a riverbed, on a flood plain, be swept into sand dunes, or collect on the ground. Over time, layers of these rock fragments build up and start to weigh down on one another. Eventually they get fused together to form sedimentary rocks. The cool thing is that, if you look closely, you can still see pieces of the original rocks or sediment that were bound together. - [Voiceover] Let's do a demo. For our rocks, we're gonna use jelly beans. Each flavor of jelly bean represents a rock or a mineral that has been broken down by wind and water through a process called erosion. We put our jelly beans in this bowl, and add some honey and corn starch, they're the bonding agents to hold our pieces together, kind of like glue for rocks. A little time and pressure has turned our jelly bean pieces of sediment into a brand-new rock. - [Voiceover] So what happens if you apply both heat and pressure? It becomes a metamorphic rock. Metamorphic rock may form by friction of the Earth's shifting crust, pressure deep within the Earth, or even radioactive decay. The heat and pressure cause the rock structure to change so it takes on a new form. Even though it's changed, you can often still see structures of its original components. - [Voiceover] Let's take our sedimentary jelly bean rock and turn it into a metamorphic one with heat and pressure. To add pressure, we'll put this heavy pot on top. For heat, we'll stick it in the oven for about 30 minutes. After it's cooled, you can see how our jelly bean rock has formed a more solid unit. However, you can still see the individual pieces of candy, but the structure has fundamentally changed. - [Voiceover] The third type of rock in the rock cycle is igneous. When rocks get super-heated deep within the Earth, they melt and form a liquid called magma. If magma rises to the surface or moves up in the Earth's crust, it begins to cool. Igneous rocks have a uniform structure throughout, but will have different properties depending on whether they cooled on the Earth's surface or within the crust. - [Voiceover] To turn our jelly bean metamorphic rock into an igneous rock, we're gonna melt it in this pot of boiling water. When our rock is cooled, you can see how all the different pieces combined to make an igneous rock, with uniform structure throughout. Pretty cool, huh? - [Voiceover] But this is only part of the story. We showed you one path for the rock cycle, but really any rock can go from one type to another. For example, igneous rocks can turn into either metamorphic or sedimentary. And metamorphic rocks don't have to become igneous rocks, they can be broken down again and become sedimentary. Or, the sedimentary rocks can get pushed deep within the Earth to form igneous. See? All of the rock types are connected, making a cycle that never ends. The end! (rock music) ♫ - We are the rocks of the world ♫ Whoa, ho ho, rocking ♫ We are rocking so much ♫ Until the night ♫ Rocking baby, whoo oh ♫ Rock it to the beat ♫ Rockin' baby ♫ Whoo, whoo ♫ Rocking until the sun comes up ♫