I'm trying to find the title/author of a pulp fiction paperback I read some 20+ years ago. The basic plot was that a magic stone/gem possessed its holders -- giving them intense charisma, arrogance, and power. Hitler held it, and people who knew about it would kill to get it. At the end, some Mexican farmer (?) digs it up unknowingly and feels it effects as the pages end.
I think it was called something like "The Charisma Gem" or "The Hitler Stone."