This specimen is a circulated coin in unc. condition. What makes it stand out at first is a mirror like luster . it is an 2018 D Pictured Rocks,that has the appearance of being struck through something. I wish my scope wasn't down....it appears to be cloth as you can see a thread like pattern in the area in question that so happens to plague both the obv. and rev. It appears on the rev. at 2 and 3 K . I don't believe that grease would leave a void with thread like markings on the surface area. what ever it was it had texture to leave a print.
I'm thinking it struck through with grit. I'd found one a while back too. Wonder if it from the same die?
Looks like a struck through grease, and the fact that it is on both sides and just small areas would seem to confirm that. It is was actually struck through a piece of cloth that small it wouldn't be on both sides and in the same place. the "threads" are probably due to lint or fibers caught in the grease.
It looks like it was some sort of paper debris. The shapes and edges make it appear like they were small pieces of paper that might have been on the planchet as it was struck rather than on the dies.
I found a 2017 p lincoln cent in an unc roll that is struck through plastic. It looks similar to your quarter. I know it was plastic because the plastic was retained in the roll. Hope this helps.
I have found several like this too but assumed it was struck through "grease"(this term is used to cover a variety of things it seems) or polishing compound. A cloth would weaken the features of the coin if it were wrapped around both sides. I rarely keep any unless they are severe. Yours is in very nice condition so I would keep it but most of them don't have any extra value. Now that I think about it I don't recall finding Washington Quarters like this, only after they started the state quarter program.
