It gives a 60% chance to save a charm when it is worn while creating summoning pouches. It has 60 charges and loses a charge for every pouch it saves a charm for. When all the charges are consumed, it breaks. Once equipped, it will become a spirit onyx (a) and not stack with other gems in the bank. Combining these gems will consolidate the charges into one gem. To maximise the amount of experience gained using a spirit onyx it is recommended to only use it while creating summoning pouches that use blue charms, as they yield the most experience.