Named as the State Gem of Nebraska, the agates are generally narrow nodules dug out of soft limestone/mudstones. Their colors are gray, colorless, white, blue, black and sometimes with bit of red color. Some agates found in the same area have strange structures sometimes in geometric patterns.  It was said that they filled in the gaps left by sponge fossils, but personally, I'm not sure about that. Their structures remind me more of evaporate mineral nodules seen in West Virginia and Michigan so it's likely that there may be once evaporate minerals like gypsum, anhyrdate or aragonite in the soft limestone/mudstone that had been dissolved and then replaced by agate.  The only hints of pseudomorphs are the thin yellowish structures within some agates. It's not known if the agates can be still be found/dug up from time to time and smaller and similar agate nodules are found in South Datokta.