This fits your. Make sure this fits by entering your model number. Gem Refill Kit Yellowstone,Montana Black Dendritic Agate Rough 8 oz Your 8 oz.(1/2 lb) bag of randomly chosen Yellowstone agates will average 3-4 large pieces. Formed as the result of volcanic activity in the Yellowstone Park area millions of years ago Attractive features of Montana agate is the colored inclusions. Some of the most beautiful Montana agates contain dendrites or tree-like plumes of mineral inclusions.