It's funny that everyone else seemed to have bought it at the time. My father worked for a company that repaired ships at sea at the time, and he apparently went out on a cruise where they harvested manganese nodules.

I don't know if it was the ship's owners figuring that if hughes wants it it must be valuable, or if it's the CIA spreading the wealth to make its cover story more plausible, but I do know he has that nodule somewhere.