I really don't know what causes a color change but I have come across several of these in different quarters. I know some other members have come across some to. Maybe someone with experience in nickel composition can tell all of us what causes this affect.Very good question.
Some kind of environmental damage, maybe it spent a winter in the grassy median of a parking lot, was found and has continued to circulate, so the damage has worn off the high spots.
I have one just like it and it has not been in a parking lot. It seems to be produced in this form. I purchased it from a dealer for $1.75 as a burnished 1999 Burnished Georgia Quarter. Maybe other collectors have the same or other ideas.
Burnished is what the mint calls tumbling the planchets in drums with steel shot to make the surface ... well like it's been hit 1000s of times by little steel balls. When the coin is struck, some of that texture comes through to the fields of the coin. If it then tarnishes slightly (and a very light yellow is not uncommon) you have a desirable (to some) effect. But this isn't that.
Pattyman did a little research on nickel tarnish. Found several coins that looked like the ops. Unable to post the links. Could not post photos because they were copyrighted. But feel free to go online and look it up they call it. (PATINA)Tarnishing.
