A rock is made of two or more different minerals. Minerals are a solid material having a uniform composition.

A rock is formed when two or more different minerals are put together. The minerals are either cemented together; squeezed and heated together; or melted and cooled together. Rocks make up most of the earth's crust. Rocks can be broken down into small pieces by wind, water or ice. This process is called erosion.

The basic types of rocks are sedimentary, igneous and metamorphic.

Sedimentary rocks form as the result of individual particles, or sediments, settling out of water or wind to form a deposit. Then, through chemical reactions and physical pressures over many thousands of years, they bond together to become rocks. When this happens it is called lithify. Examples of sedimentary rocks are limestone, dolomite, shale and sandstone.

Where can sedimentary rocks be found? A perfect example is the Grand Canyon.

illustration courtesy of Bob Ribokas

In the Grand Canyon you can find limestone, dolomite, sandstone and shale. Limestone and dolomite are also found in Iowa. Limestone is often found in Iowa along the sidewalk. It is a little gray rock. Dolomite is a little brown rock.

Igneous rocks form most mountains. In Iowa, igneous rocks are found in glacial and river deposits.

Metamorphic rocks are usually formed deep underground and are altered by heat, pressure and other conditions. Examples of metamorphic rocks are marble, quartzite and slate. Below are pictures of marble and slate tiles.

A rock can start out as one type of rock and be "metamorphosed" over time due to heat and pressure. All metamorphic rocks are made from igneous or sedimentary rocks.

Metamorphic rocks are found in Iowa in glacial and river deposits. One example of metamorphic rocks is quartzite. Quartzite is a hard rock and is used by the railroads to support the railways. If you've seen pink rock on the road, then you've seen quartzite. Quartzite was originally sandstone. Over thousands of years the sandstone was subjected to a combination of high pressures and temperatures. This caused it to change the sandstone into quartzite.

Marble and slate are two other examples. Limestone changes into marble, which is used for counter tops. 

Shale changes into slate, which is used to make blackboards.

TO: Unit 1 C. Iowa's Sedimentary Rocks and Environments

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