Lake Superior Agates Found in Iowa

These agates were found in and around the Volga and Turkey rivers. Lake Superior agates were formed during the Proterozoic period, when the North American Midcontinent Rift system developed causing the earth’s crust to pull apart. They formed near the area currently known as Lake Superior. During the Quaternary Period, the Lake Superior agates were carried southward by a series of glaciers. The impact of the glacier’s movement continued to break the agates away from the lava flow and acted as a rock tumbler giving them a rough polish and exposing their interior bands.  Lake Superior agates can generally be found in central and eastern Minnesota, northwestern Wisconsin, most of Iowa (excluding the northwest and southeast corners), southeast Nebraska, northeast Kansas and northwest Missouri. 
 

• Why are Lake Superior agates found in Iowa?

• What geological processes lead to Lake Superior agates to be deposited in Iowa?

Students could:

• Use these photos to introduce a lesson on glaciers. Show the photos and ask students if they have found an agate?
• Learn that these agates are Lake Superior Agates and that they were formed near Lake Superior. Show a map of North America, point to Lake Superior. Explain these agates were found in northeast Iowa. Encourage the students to ask questions about when they were formed and how they got to Iowa.

• PBS LearningMedia | Iowa Land and Sky: Iowa's Geological Diversity: This video contains an introduction to Iowa’s geology.
• Iowa Geological Survey (IGS) | Minerals: This article outlines the Earth materials that can be found in Iowa.
• Gitchie Gumee Agate and History Museum | Agate Basics: This site includes a map showing the distribution of agates in the midwest as well as many photos of agate examples.