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How do rocks form? |
Land Features
Stone, sand, boulders, mountains, pebbles…rocks are everywhere! Not all of them are made the same way, but there are three main groups of rocks that are divided by how the rocks form.
Igneous rocks are a type that went from hot to cold. These rocks started out as liquids, like hot magma underground or lava from volcanoes that cooled and became solid. Granite is a very common type of igneous rock.
Sedimentary rocks are formed from what’s called “sediment.” Grains of sand or tiny specks of minerals build up overtime. With enough time and pressure, they squeeze out any moisture they may have had and become one solid rock. Coal is an organic sedimentary rock, meaning that the chemicals that make it up came from things that were once alive.
The third type of rock is metamorphic rock. These rocks start out as other types of rocks but because of changes in the Earth, they change too. Temperature and pressure differences are major causes of this. It’s a little bit like when you bake cookie dough and it becomes a cookie. Adding heat changes the dough into something else (something delicious). Heat can also make rocks become something else. It’s a “metamorphosis” or change in form!
Rock Cycle
Rocks are always changing. Though it may take millions of years, any rock can change types. A metamorphic rock can melt under tremendous heat and turn into a liquid, which can then cool into an igneous rock. That same rock could then break up into smaller pieces, which might land on the bottom of a river as sediment. Over time, that sediment can become sedimentary rock.
Have you seen a picture of a water cycle? It’s a diagram where water from the ground evaporates into the sky and then rains back down to the ground. Try drawing a rock cycle.
On a paper make a triangle, and in each corner put a type of rock. Along the sides of the triangle, write down what you think would have to happen to get each type of rock to change into another. Lots of things can happen to rocks to make them change. Wind, rain, heat, earthquakes, liquids, and gravity are just a few of them. Where do those things fit on the rock cycle?
