Looks like it just toned that way from your photo but it could be plated. Gold toning is normal on those clad Quarters. Definitely not experimental. Welcome to CT.
Doesn't look like a true gold plated coin. Maybe just some reaction to a chemical which would make it Environmental Damage.
FYI, there are many companies that plate US currency and resell it. Such as this company https://www.merrickmint.com/1999-us...ed-5-coin-complete-set-with-capsules-coa.html it's considered Damaged after it gets plated. The plating is so thin it adds very little value and no value that can be extracted from it.
This..... So many folks were plating these for curio pieces back when they were released. Once folks are tired of looking at the curio item, it is taken apart and the money goes back into circulation. I have two of these gold plated quarters that I plucked from circulation.
Interesting that these "gold" quarters were sold for a profit before. My brother has a set of quarters from 2000, '01, '02, etc. that are gold plated. I think he paid $2.5/$3 per set of 5 quarters back in 2015.
Mike Mezak built himself an empire hawking these things the entire run of the series. For a specified up front fee you would get the P, D, Proof and gold plated versions as they were released. Along with a handsome "red oak" display case. Some of the best marketing had I ever witnessed at the time.
It IS possible to turn lead into gold, but it is expensive and takes some pretty high powered equipment.
