JOAN CARTAN-HANSEN: Idaho's beautiful mountains may look really solid but like all rocks, they're constantly changing. It has to do with the rock cycle.

There are three major types of rocks - igneous, sedimentary and metamorphic. Igneous rocks are formed when magma cools and becomes solid. This can happen below the surface of the earth's crust or closer to the surface like in the pits of volcanoes. Most of the earth is made up of igneous rock.

Now sedimentary rocks are formed when stuff like sand and dirt are put down in layers then squeezed by a large amount of pressure until the layers become solid. Over 75% of the Earth's land surface is covered by sedimentary rock.

Metamorphic rocks are rocks that already existed but were transformed by heat or pressure.

Now as soon as rocks are formed they begin to change. Rocks break down into smaller pieces through weathering. Heat, wind, water freezing and thawing can all wear away and crack apart rocks. Plants and animals break up rocks too. The particles of the original rocks are removed by erosion or swept away or blown away to a new location. When the deposits are buried, heat and pressure make them into new rocks and the rock cycle begins all over again.

How rocks are formed is one way to classify or identify rocks. Another way is to figure out what it's made of. A rock is made up of one or more minerals. Minerals are made up of one or more of 92 different natural elements that combine together in different ways. Some rocks like gold and diamonds are very valuable and others are well, useful for a good skipping stone. Rocks take a long time to form and they're always changing. We live on them, build our homes out of them, even wear them.

Rocks and minerals are essential to our lives.

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