Sand Pearl
From Final Fantasy Wiki
The Sand Pearl, also known as the Sand Ruby and Desert Light in Japan, is the only known cure for the illness Desert Fever, which befalls Rosa in Final Fantasy IV. With the help of Edward and Rydia, Cecil obtains the pearl from the Antlion's Den to cure Rosa.
In Final Fantasy IV: The After Years, Edward must find the Sand Pearl during the Full Moon for Harley, who succumbs to Desert Fever in Kaipo.
