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Rock Cycle Essay

The Rock Cycle
The Earth Recycles

The Rock Cycle chart below shows each type of rock connected by arrows. The arrows point from one rock form to a new form that it can become over time and exposure.

The Rock Cycle describes the process the earth uses to recycle rocks. Yes, even rocks are recycled.

Types of Rocks

There are three basic types of rocks: igneous, metamorphic, and sedimentary. The interesting part of knowing these names is that any one of the three types of rock can be changed into one of the other types.

Naming Rock Types

The names of the rock types refer to the way the rocks are formed.  Igneous rocks are formed from fiery molten magma. Metamorphic rocks form under intense heat and pressure. Sedimentary rocks form by weathering.

Chart of The Rock Cycle

Click on the picture if you want to learn more about that type of rock. For details on how rocks change from one form to another, click on the arrow. You’ll read about how rocks can change from one form to another.

The ROCK CYCLE describes the process the earth uses to recycle the rocks and soil that make up its layers. 

The ROCK CYCLE chart below shows a photograph of each type of rock: igneous, sedimentary, and metamorphic. These are the three basic types of rock and they can change from one type to another through processes of heat, pressure, and weathering. 

Arrows connect the different types of rocks. Sedimentary rocks can become igneous rock as they are pushed down from the earth’s surface into the intensely hot inner layers of the earth.  Once there, the rock melts, becoming magma that then forces its way up to the surface again. Along the way, the rock might change under pressure. This makes different degrees of metamorphic rock. 

Let’s take a closer look at each type.

Igneous Rocks
Igneous rocks are formed of magma, the molten form of the earth’s mantle layer. Igneous rocks can form above ground as lava spewing from volcanoes. But igneous rocks can also form below the surface. Pockets of magma get stuck in layers of the earth. As they get closer and closer to the surface, the magma slowly cools. Granite is an igneous rock that formed from a slow-cooling pocket of magma.

Igneous rocks are made of magma. Magma is the molten form of Earth’s mantle layer Igneous rocks can form above or below ground. Intrusive Igneous rocks are the igneous rocks that form below ground. Examples of intrusive igneous rocks are granite, diorite, gabbropegmatite, and peridotite

Extrusive igneous rocks form when the molten lave spews from volcanoes. Examples of Extrusive Igneous rocks are basalt, rhyolite, pumice, scoria, and obsidian.

Extrusive igneous rocks can blast out of the earth with great force or the can ooze and flow almost like water. How the magma is ejected from the volcano depends on what it is made of and how much gasses are present. Lots of gasses makes bubbles in the lava. Pumice has so much gas that it is very light  and they can even float in water! 

Intrusive igneous rocks form underground in chambers or pockets of molten magma. Stuck between layers of the earth, they force their way toward the surface. As they move closer to the top, the molton magma cools. If it becomes cool enough to become solid, different types of rock form. Granite is one type of intrusive igneous rock that has solidified beneath the surface from molten magma. 

Pictured below left: basalt lava   right:granite

Sedimentary Rocks
Sedimentary rocks form from small weathered particles of other rocks or the weathered shells of sea animals. Wind and rain beating on the faces of exposed rock tend to wear off particles that are blown or washed to a new location. When sea creatures die, the shells settle on the bottom of the ocean. As the sediments pile up, they press together to form Sedimentary rock. 

It’s easy to remember what sedimentary rocks are: they are rocks formed from sediments. Sediments are tiny particles worn off of other rocks by wind, rain, extreme temperatures or extreme weather events such as hurricanes or earthquakes. 

Pictured below left: sandstone       right: conglomerate


Metamorphic Rocks
Metamorphic Rocks form under intense heat and pressure. Metamorphic rocks start out as igneous rocks, sedimentary rocks or other types of metamorphic rocks, but through heat or pressure, change characteristics such as sheen, tightness of grain and hardness.

Pictured below: left: gneiss       right: shist


Summarizing The Rock Cycle

Rocks continually change form. What started out as sedimentary rock may change to metamorphic and, with time and weathering, change back to sedimentary.

Rock Cycle Lesson Plan



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