No mint mark. has normal looking clad outer, then Cu but another silver colored metal sandwiched in between the Cu layers, all the way around. What kind of planchet was this?
Seems like top and bottom nickel overlays the copper and hides it. Seems like an absolutely average copper-nickel quarter. Weigh it to be sure.
The first 3 words of the OP are: No mint mark. 50 cents would be double face I'll weigh it at the next group weigh party ... but with all those huge tolerances would it even matter? weight never seems to be definitive.
If you really want to know more about the layers of metal in your quarter grab a piece of sand paper and sand the crud off the reeded edge to see what it consists of. heck after a year or so in use anything can be hiding there in the reeds.
The stuff is not jammed down in there, it is the metal that the coin is made of. I'll get a better image later, too busy now. That first one was monkey biz with my new toy, I can do much better.
when I said sand off the crud I meant the built up layer of built up toning . after a while the new coins will become all kinds of different colors , sand this off and see what it looks like. your quarter will still be worth a quarter. don't play with that new toy too much or it will get you in trouble