Montana agate is usually transparent with red and black ribbons of color and sometimes black moss like inclusions. Montana agate is most often discovered in the gravel deposits around the Yellowstone River and tributaries. Agates are hard stones between 6.5 and 8 on the Mohs Scale. Agate is the suggested stone on 12th and 14th wedding anniversaries and is also the Gemini birth stone. View a full selection of Montana agate jewelry by shopping our online selection below or stopping by our Missoula, MT, jewelry store today.