I left my aluminium moka pot unused for a year and it turn out to be so rusty. I think it was too damp at my outer kitchen. Is there a way to revive it?
That looks very much like aluminum oxide, caused by exposure of aluminum to oxygen in the air. Don't worry. However unsightly it looks, it's not dangerous. You should be able to remove it with white vinegar or a solution of vinegar in water. Wet a soft cloth or soft-bristled brush with it and gently scrub.