What can cause course salt to melt? If you put it on a flat surface, can it melt on its own into water? What causes this reaction to make the salt melt?
Salts can't "melt" at room temperature, much less into a water solution. What might happen for some salts is that they're able to draw humidity from the environment with such avidity that they become a liquid solution. If a compund can do this we call it deliquescent.