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SCHOOL
OF ROCK

Welcome to Earth ... the third rock from the sun!

Rocks are amazing because they hold important clues about our planet. They reveal information about remote places we can't visit and distant times in the past. 

Scientists may not be able to travel inside an erupting volcano, to the bottom of the ocean, or across the solar system; but they can learn about the conditions in these places from rocks they collect.

Minerals make the difference.

Whether it's a rock in your backyard or in a canyon wall, almost every rock you've ever seen is made of minerals. Rocks are different from each other because they contain different types and amounts of minerals. One way scientists identify rocks is by looking closely at their minerals. For example, the rock sandstone is made of the mineral quartz. The rock granite contains quartz too, but it also has other minerals like mica and feldspar.

The kinds of minerals in a rock give clues to where the rocks formed. A rock with the mineral garnet probably formed deep in Earth, like under a mountain. A rock with the mineral muscovite probably formed on land.

Rocks come in all sizes, shapes, colors, and textures.

​Despite their differences, there are three basic types of rocks: igneous, sedimentary, and metamorphic. 

 

​Igneous (IG-nee-us) rocks form from melted rock, or magma, that comes from inside Earth. Sometimes the magma erupts from a volcano, and then cools and hardens at Earth's surface. Magma can also cool slowly and form rocks underground. Igneous rocks are brand-new rocks. They don't form from other rocks. Igneous rocks include pumice, granite (below) and obsidian.

Sedimentary (sed-uh-MEN-tuh-ree) rocks form from tiny pieces of rock that are broken down by wind and water. Over time, these pieces settle in layers with sand, silt, dead plants, and animal skeletons. These sediments are squeezed by other sediments above them until they cement together to form a rock. Sedimentary rocks include sandstone, chalk and limestone (below).

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​​Metamorphic (meh-tuh-MOR-fik) rocks form from igneous, sedimentary, and even other metamorphic rocks deep in Earth's crust. When these rocks are heated and squeezed, they slowly change into new, metamorphic rocks. Metamorphic rocks include gneiss, slate and marble (below).

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Standing on limestone.

Since you're here visiting the School of Rock, we can only assume that you are somewhere around the Whalon Lake Preserve or walking along the DuPage River Trail. Wherever you are, you're standing on limestone, a sedimentary rock formed over time that contains, sand, silt, dead plants and animal skeletons! Pretty cool! 

In fact, Whalon Lake was formerly a limestone quarry which has since been converted into an 80-acre public fishing lake.

The nearby Barber's Corner Quarry operated by Vulcan Materials Company sits on approximately 550 acres of land and is just to the east of Whalon Lake. The deepest part of the quarry is close to 150' below the surrounding ground level. That's 2 mature pines trees stacked on top of each other, or 5 flag poles stacked end-to-end! Because limestone is widely available and quite durable, humans have used it to build things for millennia. The majority of the limestone that is mined from the Barber's Corner Quarry is used to make concrete and other construction materials. 

Wait ... animal skeletons?

Yes, remember, limestone is a sedimentary rock, layers upon layers of dead and decaying "nature stuff" squeezed together by increasing pressure. It's like when someone yells "monkey pile" and you're on the bottom. If you stayed there long enough, you'd be flat as a pancake! 

So, where do the animal skeletons come in? Well, more than 400 million years ago, most of Illinois was covered by a shallow tropical sea. It's what scientists refer to as the Silurian Period. During this period, sea creatures ruled! In fact, this was the only time reefs grew in Illinois.

Over long, long periods of time, layers of shells and mud built up and the lower layers (think "monkey pile") slowly hardened to rock which we know today as limestone. 

To learn more about the Silurian Period: Paleozoic | Silurian Reef | The Field Museum

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