There are three types of rock: sedimentary, metamorphic and igneous. Let’s explore these amazing treasures together!
- Sedimentary Rocks
Sedimentary rocks are formed from old rock, along with hard parts of plants, shells and bones that accumulate on the Earth’s surface.
There are three different types of sedimentary rocks: clastic, biologic and chemical.
| Type | Example | Characteristics | One of the parks where it can be found |
| clastic | sandstone | composed of pieces of other rocks | Grand Canyon National Park, Arizona |
| biologic | coal | composed of hard biological materials | Guadalupe Mountains National Park, Texas |
| chemical | limestone | formed by chemical precipitation | White Sands National Monument, New Mexico |
Key Term
Chemical Precipitation: happens when a solid forms out of a liquid during a chemical reaction.
- Metamorphic Rocks
Did you know metamorphic rocks are formed from existing rocks that undergo heat or pressure? To form these rocks, it is essential for the original rock to stay solid and not melt. If the temperature or pressure is too high, the rock will melt and turn into magma, which is a very hot liquid and semi-liquid rock found beneath the Earth’s surface. When it erupts and reaches the surface, it is referred to as lava. When the rock turns into magma, it creates igneous rock instead of metamorphic rock.
Metamorphic rocks usually form deep underground, but guess what? They can end up on the Earth’s surface due to natural processes. They are usually harder than sedimentary rocks and they can be found in mountainous areas, which suggests that ancient mountains once existed in places that are now low hills.
Metamorphic rocks have two classes: foliated and non-foliated.
| Class | Example | Appearance | One of the parks where it can be found |
| foliated | slate | has layers | Antietam National Battlefield, Maryland |
| non-foliated | marble | no layers | City of Rocks National Reserve, Idaho |
- Igneous Rocks
Think of igneous rocks as the cool ice pops of the rock world! Just like ice pops cool down, igneous rocks are created when hot lava or magma cools down and solidifies. These rocks are named based on specific combinations of their minerals, overall chemical composition, and their igneous texture.
Igneous rocks can be classified into two categories: intrusive and extrusive.
| Category | Example | Where it’s formed | Cooling | One of the parks where it can be found |
| intrusive | granite | inside the Earth | slow | Joshua Tree National Park, California
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| extrusive | pumice | on the surface of the Earth | quick | Sunset Crater Volcano National Monument, Arizona
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