Activity 1: Types of Rocks

Diagram of the rock cycle.

USGS and NPS Photo

The rock cycle is a long and slow journey!

The rock cycle diagram (left) shows the different geologic processes where the three types of rock are found.

Rocks deep in the Earth move and change over time, eventually making their way to the surface, then back deep into the ground to start the cycle again.

The three main kinds of rock are igneous, sedimentary, and metamorphic. Each type of rock moves through the cycle in different ways.

In this activity you will learn about the three different types of rocks and complete an at-home rock identification activity!

 

Sedimentary Rocks

Sedimentary rocks are made when sand, mud, and pebbles are laid down in layers. They are classified into three groups: Clastic, Biologic, and Chemical. These layers are packed under more and more layers as time goes by. Eventually, the layers will lithify and turn into rock. You can find these rocks in deserts, lakes, rivers, and oceans. Unique layers of sedimentary rocks define many of the picturesque views of the desert southwest!

More About Sedimentary Rocks

 

Left to Right: a) A typical clastic sedimentary rock, sandstone, appears red due to iron oxide. b) Coquina (biologic sedimentary rock) is a rock composed primarily of marine fragments. c) Castile Evaporite (chemical sedimentary rock) of southeastern New Mexico and West Texas.

NPS Photos / Tina Kuhn

 

Igneous Rocks

Igneous rocks (from the Greek word for "fire") form when hot, molten rock (magma) cools and hardens either below (plutonic) or above (volcanic) the Earth's surface. Magma originates deep within the Earth, near active plate boundaries or hot spots. Magma that rises to the surface is called lava. Igneous rocks are classified into two groups depending upon where the molten rock solidifies: Extrusive or Intrusive.

More About Igneous Rocks

 

Examples of igneous rock textures. Pictured left to right: a) Felsic rhyolite with an aphanitic texture. b) Obsidian is a volcanic glass with a conchoidal fracture. c) Diorite is a classic "salt and pepper" rock with a phaneritic texture. d) In this specimen of rhyolite porphyry, phenocrysts of obsidian are surrounded by a fine matrix.

NPS Photos / Tina Kuhn

 

Metamorphic Rocks

Metamorphic rocks are made by high temperatures and high pressure. As heat and pressure increases, the rock changes, stretching, twisting, and folding as it cools. In metamorphic rocks, minerals from the original rock form new minerals, like gneiss, quartzite, or marble. Another example is slate, which was originally black mud on the bottom of the sea or lake. Metamorphic rocks are often found in mountainous regions. Fossils can sometimes be found in metamorphic rocks but they are often squashed in the process.

More About Metamorphic Rocks

 

Pictured left to right: a) Foliated metamorphic gneiss. Foliated rocks are types of metamorphic rock that have parallel bands of grain. b) Non-foliated metamorphic soapstone. Non-foliated rocks are types of metamorphic rock that have no arrangement or bands of grain.

NPS Photos / a) Tim Connors b) Tina Kuhn

 

#FindYourPark Activity

The National Park Service encourages its visitors to #FindYourPark to spread the word about the amazing places we manage, the inspirational stories each Park preserves, important natural resources, and our diverse cultural heritage!

Directions:

1. Click the "More About" links in the previous sections and check out National Parks across the country to find examples of different rocks.
2. Find at least three different Parks that have either sedimentary, igneous, or metamorphic rocks. On each Park site, find a cool rock that you would like to learn more about.
3. Using your Junior Geoscientist Activity Log, record 1 observation for each rock type. Make sure to include the Park name, a one-sentence description on the rock you chose, and a drawing of your rock example!
4. Once you've logged at least 3 observations, continue to the next activity in the Junior Geoscientist program.

 

Reflection

What types of rocks are around you? Take a walk and explore your local park, stream, or even your backyard. What rocks do you find? What types of landscapes are near you? How does this relate to the rocks you find?

 

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