It's established when a mortal touches an Infinity Stone, they die.
We've seen the effects three have on mortals already.
- Tesseract - Burns the victim and transports the body/charred remains to Yggdrasil. (Seen with Red Skull)
- Aether - Enters the victim and will slowly kill them unless removed. (Seen with Jane Foster, who survived coz Malekith absorbed it from her)
- Orb - Destroys the victim outright. (Seen with Carina)
So what happens when a mortal touches any of the other three Infinity Stones? We never really saw that, did we?
My guess for the Eye of Agamotto is that it causes them to age into dust.
My guess for the Mind Stone? Maybe causes their brain to explode or something?
And as for the Soul Stone... well, we haven't seen what it can do yet, so it's too early to speculate on it.