Igneous rocks are formed when lava or magma cools and hardens.

The rocks are "born" as volcanic eruptions eject massive amounts of magma onto Earth's surface. Remember that magma is nothing more than a large body of hot liquid rock and minerals. As the magma cools into a solid rock around the base of the volcano, it can be collected as samples of rocks such as basalt, pumice, or obsidian.

Traveling east to Zion National Park in Utah, tourists would find the well-known Navajo Sandstone Formation. It looks like a towering sand dune that has been permanently solidified against the landscape. The sandstone rocks that make up the Navajo Sandstone Formation began millions of years ago as tiny grains of sand in a prehistoric desert. Over time, winds carried the sand and deposited it into giant sand dunes. The pressure of each new sand deposit caused the sand underneath to compact and cement together into solid rock.

Checkerboard Mesa in Zion National Park, Utah is the remains of an ancient sand dune.

Although these sandstone rocks began as a collection of individual grains of sand, the sand grains themselves had to come from somewhere and something else. Where might these sand grains may have originated?

Geologists theorize that the sand grains may have broken off a larger rock formed earlier by a volcanic eruption. Or they may have broken off older sandstone rocks. Because the Earth is so dynamic, rocks are always changing. Minerals that make up rocks are constantly moved and acted upon by the environment. Environmental agents change one type of rock into an entirely new rock. The web of environmental processes that forms and changes rocks is known as the ROCK CYCLE.

Courtesy of the Mineralogical Society of America

Rock Cycle

The rocks on Earth cycle among the following three categories:

Types of Rocks Type Characteristics Examples Igneous rocks Igneous rocks are created when molten material such as magma (within the Earth) or lava (on the surface) cools and hardens. The hot material crystallizes into different minerals. The properties and sizes of the various crystals depend on the magma's composition and its rate of cooling. Granite Obsidian Basalt Pumice Andesite Diorite Rhyolite Sedimentary rocks Sedimentary rocks are made up of sediments eroded from igneous, metamorphic, other sedimentary rocks, and even the remains of dead plants and animals. These materials are deposited in layers, or strata, and then are squeezed and compressed into rock. Most fossils are found in sedimentary rocks. Sandstone Shale Conglomerate Limestone Chert Coal Gypsum Metamorphic rocks Metamorphic rocks are produced when sedimentary or igneous rocks are transformed by heat and/or pressure. The word "metamorphic" comes from the Greek language, which means "to change form." Marble Slate Quartzite Schist Gneiss

To gain an idea of how the rock cycle works, the world rock tour that began in Hawaii might end in east Greenland. Millions of years ago there, magma deep inside the Earth forced its way into another rock and solidified. This created an igneous rock. Then, intense pressure in the Earth caused the rock to up-heave, fold, and crumple, until it became an entirely new rock: a metamorphic rock. That new rock now makes up a mountain formation in Greenland.

In this interactive schematic of the rock cycle find out how rocks are formed and destroyed.

And the rock cycle continues today. Everyday, little pieces of the mountain rock are worn away by water and wind. Those pieces collect somewhere and are compressed into new sedimentary rocks, which will continue to change and reenter the cycle as different metamorphic rocks or as melted material that can form new igneous rock. Then the process will begin all over again.

The rock cycle never ends.

		I, Rock: Sandy Stone said to her son, "Rocky, I remember when you were just a cute little grain of sand..." Tell the story of a rock's progression through the rock cycle.

For Fun!

Monumental Stones Instructions: Click and drag the circled numbers onto the correct images. You can click any picture at any time to see an enlargement. When all circled numbers are placed onto pictures, click "Submit." If you got some wrong, try again and again click "Submit." When completed correctly, hover over each picture to find more information. Click Here!