one more quick question.... Is it poisonous if it was coated in mercury?
Yes, ALL forms of mercury are poisonous. But tiny amounts are seen as "harmless" by some, but a major health hazard by others. I personally lean towards the harmless end to the extent that I, and hundreds of millions of other people, have grown up with amalgam fillings without any identifiable problems.
And here's another little trick similar to the penny that I used to do as a kid that's probably a lot more "dangerous" by current standards: When I was a kid, my father brought home about a pint of mercury from work one day. Now this is back in the 50s, and our silver money was, well, silver! He showed me that you could dip a silver coin into the mercury, and the mercury would stick to the silver. Moreover, you could smear that little bit around to cover the whole coin giving it a wet looking, extremely bright and even silverier silver color than the actual silver! ;-)
Only for a little while, though. As the mercury leached the silver in the coin, it would soon turn the dull grey color of amalgam.
Now cavalier as I may be about some of the crap I've pulled over the years, there's one thing you DON'T want to do with mercury, and that's to heat it. Mercury vapor in small amounts is both deadly and fast, and there are more than a few gold prospectors in the afterlife who could attest to that fact if they could.