Please help! What is this green stuff?

My brother gave me two Canadian Millenium Quarter sets.  In both of the sets, there are patches of green on some of the quarters.  I'm not sure what this is.  I don't believe the quarters are silver and they aren't covered by any plastics.  Maybe it's mold?  Any thoughts?  Thanks.

I believe that is what they call bronze disease.

http://www.essortment.com/collecting-coins-coin-cleaning-58575.html

Verdegris, it will eat into the metal slowly corroding the coin.