Pinching Calcified Pennies

Seeing how the weather had improved, I took a walk along the shore of Shell Bank Creek.
After about two hours of finding nothing interesting (beside a whole lot of dead horseshoe crabs), I decided to head back to the car.
Almost immediately after turning around, I looked down to find a penny.

I tried to clean it off, but to no avail. That stuff is caked on for the life of it.