1979 Washington Quarter With Copper Backside?!

Hello and

Hard to tell, but I suspect that your coin has environmental damage. Cupro-nickel typically tarnishes to a dark brown color when buried, and I've found similar ones when metal detecting. If one side of the coin was protected while buried - perhaps because it was against the side of a purse or another coin, it could come out of the ground clean on one side and dark brown on the other.

What is the weight, please?

To CCF! Just a damaged coin with Post Strike Damage ( PSD). Not an error coin.

I don't know much about coins, but I hardly think this is environmental damage. The coin is LIGHTER than the standard quarters. I have a scale that says it weighs less. I made a video here is the link to view on Youtube for color, sound and weight to see in detail. Thank you for all of your help, I'm so curious!

Video not working.

Still not working, But I can slide the scroll bar enough to see it is a coin that was found outdoors. Someone maybe have buffed off the red color on the obverse and left the corrosion on the reverse. But that is how coin found outdoors look.

When they are carry in a pocket for sometime, the higher devices return to silver in color and eventually more color comes back:

The red turns to black eventually.



If the cladding is missing the color will be a lot darker:

The coin will be lighter in weight and have a weaker strike. (on both sides) Note the coin above. On a normal coin found outdoors, the color is present, but the weakness of the strike will be full.

Saw your video. Your scale is the wrong scale for weighing grams and lower, its for pounds and ounces. And its rounding. Ideally it should have 2 or more decimal places,after the gram. The scale isn't accurate because it's not sensitive enough for lighter weights.. A quarter should weigh 5.67g. So obviously your scale is rounding and appears to be rounding down to a round gram and unable to do. Ideally grams should be the highest it could go up to an ounce or so, maybe 1 pound tops, it needs to be able to go down to centigrams or decigrams, even milligrams to have the sensitivity to weight coins accurately.
A postal scale doesn't cut it, some kitchen scales can do it, a jeweler scale or pharmacist scale could do it.

Even with that scale, to round down to 4 grams would mean the coin would have to weigh less than 4.5 grams. It is a good sign, but I would really prefer to see a more accurate weight, is grams to two places.