@wilburton it looks to me like environmental or chemical exposure stained the copper plating. By "green stuff", you might mean verdegris, bronze disease, or PVC slime but I don't think that this coin has any of those.
Also, it is not a big deal, but in seeing @crazyb0's response, please consider being a little more descriptive with your initial posts. Being more specific with your question or concerns can be pretty useful. Just my
Two Cents and now I will get off of my soapbox.

"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz