Power
You have the power to determine if a diamond is worth a fortune, or if it's a fake. How you use that power is up to you.
You should probably use it for good and tell people the true value of Great-Aunt Jenny's ring. The alternative will likely result in karma biting you for it in the end.
You also may have the power to create synthetic diamonds. How cool is that? Say you want to get married but can't afford a rock—just whip up a nice two carat. You gotta love the power of chemistry.