Again, I'm going through alot of change and this one caught my eye. It a dark grey mixed in with nickel from wear. Is this something you guys can answer as far as seeing often?
That's right except the war nickels which have approximately a third of silver. That would only cover the years 1942 through 1945 tho!!.
I would guess it was a dug coin, acidic soil conditions no less, some type of environmental damage to the exposed surfaces. BTW....cameo appearances generally appear of proof coinage, 1988 would have had the "S" mint mark for San Francisco where the proofs were coined.
That type of discoloration is very common - I'd say that I see it on nickels more than on any other coin. Joe