Having the "mission-item" attribute, it's an item that was designed to appear in a mission. It can't be the item that you bring back to the king/pub for your reward since it's created from three commonly available items. It's probably used to create another mission item such as in the case of the the ruby gemma and Ogoshi's crossbar. If this is the case, the essense-pebble is probably an ingredient in a recipe which includes an item that can only be found in a mission. Now the question is does this item appear in a current mission, a future mission, or none at all?
How did you find the recipe? If you found it in the pub, what level was the character that found it?