I am not an expert, but it is probably a high school chemistry demonstration or possibly plated for jewelry. Possibly environmental exposure, although it doesn't look to have been in the ground. It is also possible somebody plated it to try to pass it off as one of the then-new golden dollars. You might check the weight on the odd chance it is a dollar planchet, but I would think that highly unlikely if not impossible, not just because such would be rare but because the dollars are slightly larger in diameter than quarters.
Back when the state quarters came out Mike Mezack built a TV coin empire marketing these. Send him ten bucks a month and you would get an uncirculated state quarter and a gold plated state quarter to be proudly displayed in his presentation case.... He sold a lot of these... Now twenty-five years later they get passed down and taken to coin dealers who won't buy them so they find their way back into circulation.
Littleton still sells them. Probably other places too. https://www.littletoncoin.com/shop/search?searchTerm=gold%20plated%20quarter
I have a couple gold plated quarters. I have a New Jersey that is plated, IDK with what but the edge shows no copper.
