Montana Agate is a stunning chalcedony found abundantly in the gravels of the Yellowstone river. Montana Agate, was formed like all agates over many years of silica from volcanic ash, water, and other mineral oxides that form the bands and inclusions in the stone over a long period of time. Large portion of agate are found in the region where all this occurs so they are formed, but once they are dug out they are gone unless a new deposit is found. Being an agate, it has a moh's hardness of about a 7. Montana Agate is truly an unique gem to the Yellowstone region.