Hello there bugmanmiller. This posting was done quite some time ago but I'm curious to know if you still have this quarter and if you ever weighed the quarter on a better, more accurate scale. I too found a 1980 black quarter that was entirely smooth (edges and both sides) and significantly underweight. It appears to look different than the other black coin images provided to you. There is no damage to the coin (scrapes, scratches, knicks, etc). It still has nice detail. I searched the quarter and find this post as well as a couple others in different forums that provided much of the same description. I'm wondering if it just a coincidence and they are all results of environmental damage or if there's more to it!!

Any updates from you or others would be much appreciated. Thank you!