unknown type of zorkmid,  
possibly an Obolus

The obolus (plural oboli) is an ancient silver coin. It had been a custom to bury the dead with an obolus to pay to Charon so their soul could pay the fair across the River Styx to the main region of Hades. Eventually, by the eleventh century GUE, Charon had claimed to have accounted for every obolus in the aboveground and began to replace the fair with zorkmids instead.

SOURCE(S): The Zork Chronicles, Return to Zork