>Mercury
When I was a kid I ran a cinnabar smelter, condensed the mercury vapor in an old still from prohibition. I sold the mercury to the local gold miners to buy guns and ammo.
At the end of the mining season, I took it to school and shared it with classmates as back then, you could rub a penny to coat it and fool some nickel coke machines to give you a coke for a shiny penny.
I am near 80 and can still do math in my head and read 1,200 words a minute. I believe the hype about it is vastly over stated.