How to farm sulphites?

Hi everyone,

I Just've started the game and having so much fun and seems like finished the current missions on act 4 but stuck on a mission where Niko wants 20 Azurites. Currently i have 14 of them and 7 of sulphurites. To progress i need 8 sulphurites but don't know where to get them. What can i do?

Continue your travel in Wraeclast and get another Sulphite apparition. Then go back to Niko and finish this quest.