On the flats around Chadron specimen of a weak bluish colored vein agate are found  beside the classical “Fairburn agates”. Often the specimen show a very dark, nearly black first layer which still strengthens the luminosity of the central blue agate in contrast.

These agates likewise formed like the “Fairburn agates” in sediments, however in the Chadron formation from the Oligocene (about 30 million years old). The Nebraska Blue Agate is the national stone of Nebraska.