Nice chunk of agate in host rock. The thickness gives it the bluish color. The thinner the slice, the more grey it will be. Born and raised north of Marysville. Did you find it in a new rock pit in the mountains? Or a new rock slide? It looks fresh. Had I found it, I would call it a keeper, as for value, not so much, although what people pay for minerals on ebay surprises me. Good luck. That is not an Ellensburg Blue.