It looks to me more like removal of a layer to me rather than a deposit of something. Notice how the copper remains on the high points of the obverse. I know zinc deposits will make copper coins look silverish, but the spots where the copper remains on this coin made me think it's something else. I don't know though, and am certainly no expert.
If you remove a layer of Bronze (.950 Copper and .050 Tin & Zinc) from the coin, you still have Bronze! It looks like that it was some kind of plating job that went wrong or like Topher stated, a mineral deposit. Frank
I know that pre-1982 cents aren't layered, it just looked more like that to me because of the way the copper remains on the high points. I suppose there could have been some liquid sitting shallow in the coin, leaving the high points above, and that contributed to some deposits like this. Just interesting to try to figure out what caused this. Thanks for the posts.
