Together with the very rare Fairburn-agates the much more common Prairie-agate is occuring in the same areas in South Dakota, Nebraska and Wyoming.
Prairie-Agate is a non banded variety of chalcedony. Its pattern is remaining at petrified stromatolithic algae. In the european area such a type of chalcedony is called chert or flint. Prairie-agates are formed in the same sediments as the Fairburn-agates.
Usually these agates are showing a greyish-brown to yellowish pattern on a pinkish, whitish or very rare on a reddish ground.
Only very seldom they show a colourful and nicely contrasting pattern. This pattern is caused by the “Liesegang-Phenomenon”.