1974 Quarter Possible Wrong Planchette

Yep @spruett001 is correct--your quarter has been exposed to a chemical or the environment which has stained the surface. If you check the weight, you should find it within tolerance.

Note how circulation is already removing the haste off the coin. In a short time in circulation this will turn silver colored again on the high spots. A missing cladding would not turn silver, it would remain a copper colored. Spendable or carry it in your pocket and watch it change back to normal.

It looks more like an "accidental" plating incident to me than it does say in-ground environmental damage..

Plating like that can easily happen when you have a bunch of pocket change, especially if it happens to be 'mixed heritage' change (by that I mean including foreign coins not minted out of the same metals combinations used in the US) all tossed together into even a weak acidic solution (i.e. vinegar and water) and let sit between agitations for a period of time -- as an example while trying to dissolve what's holding beach sand & etc stuff loose from coins enough to be able to run them through coinstar machines without creating jam-ups..

Weak solution plating tends to look like that quarter -- fairly evenly toned and not necessarily having yet completely coating all recesses of the coin, while in-ground environmental changes to coinage, especially clads, tends to be much more invasive, violent if you will, all-encompasing, with the possibility of immediate-and-abutting changes from one mineral to another not uncommon..

Anyhowww, yeah -- I've done a bit of metal detecting down through the years lol..

Swamp