Visitors can find all three types of rocks at Crater of Diamonds State Park: sedimentary, metamorphic, and igneous. Each of the rocks are formed through physical changes, such as erosion or compacting. A conglomerate is a sedimentary rock made of other rocks glued together, like nature’s concrete!
A conglomerate has a variety of colorful rocks cemented together. The rounded rocks found in conglomerates are referred to as clasts. The clasts found in Crater conglomerates are mainly novaculite, chert, and sandstone cemented together by iron oxides. They are rounded due to erosion, as they were transported from their original sources by rivers, ocean waves, or glaciers.
Crater conglomerates have made quite the journey to end up here at the park! The rocks in some conglomerates found at the Crater originated from the nearby Ouachita Mountains and were transported through waterways that changed through courses over hundreds of thousands of years!
This process started during the Cretaceous Period, when Arkansas was under water. It’s hard to imagine that Arkansas once had a coastline! High waves tossed out clay and fine sand, making a gravel coastline.
As gravel beds compacted together from rising and falling sea levels, sediments and dissolved chemicals such as iron oxides cemented the rocks together, creating conglomerates. This type is called ironstone conglomerate.
Conglomerates were created after the formation and burial of the Prairie Creek diatreme, the volcano that bought diamonds to southwest Arkansas. Due to a diamond’s negative charge, you cannot find diamonds in conglomerates. However, that doesn’t mean conglomerates are not worth collecting; they make up less than one percent of all sedimentary rocks worldwide! Because of their multiple colors and hard, solid structure, conglomerates are often used in construction or as decorative stones in jewelry or other ornamentation.
Whether you come to search for diamonds or to learn about its fascinating geologic history, we hope you visit the Crater of Diamonds State Park soon! For more information, visit www.CraterofDiamondsStatePark.com, call 870-285-3113, or email [email protected].