This is kind of agate which is widely mistakened as the Fairburn Agates. They appear to be some kind of chert nodules that have been rounded by weathering. Such weathering gave the agates the wave-like patterns of black, tan and white colors on the surface and most agates are tan to white inside, sometimes with red colors. What distinguished the Prairie agates from Fairburn agates are their large sizes and irregular patterns.  The chert nodules were so abundant that they tend to show up in many old rough collections or end up as one of most unwanted rocks. I even don't want them.

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