1960 silver penny? Coin roll hunt!

[TrpnBils]

Mercury is a liquid at room temperature (all the way down to almost -40F actually). You couldn't coat it with mercury any more than you could coat it with Mountain Dew. It's a zinc plated (and a poor job at that because it still retained some copper color) penny. Here's some examples of some well-plated ones. The pic at the bottom shows a copper penny, a zinc plated copper penny, and a brass (i.e. "gold") plated one that is the result of heating one of the zinc-plated ones. The one in the OP's picture is not as well plated as this one, which means it was either done with a weaker base or wasn't left in the chemical bath long enough.

Turn Copper Pennies Into Silver and Gold Pennies