FYI the black stuff is probably just tarnish, very common on silver coins, the only way to prevent it is to keep the coin sealed in an airtight holder, this coin is in great shape for a 100yr. old circulated coin.
I took my thumb and tried to wipe it off but it wouldn't come off. Maybe there is something that will take it off because your right it is in great shape with all details.
I'm not sure it will come off. When I saw it would not come off I quit. It doesn't make since. I thought that tarnish wiped right off. Well I will leave the cleaning up to the bidder.I know there should be something to clean it. You would not want to keep it the way it is.