Gym leader of Olivine needs your help. Her favourite pokemon is in bad form and needs medicine. You have to gather items that are needed for it: 20 chikorita's leaf and 25 chesto berry.
Chikorita's leaf can be obtained from chikorita.
Chesto berry can be obtained from "Harvest".
After gathering items come back to Jasmine, in reward you will be able to challenge her for Mineral Badge.