Not the rarest or most special by any means, but its one of the cleanest Proof Franklins I've ever seen.
Found this in a dealers stock. It had a thread of duct tape, or something similar laying on it which caused the toning.
Nice try...I just checked it out The difference is the mintmark for each of the year, and it affects all six coins, not just the quarters. The Type I for 1979 is a "blob," a rectangular mound, with a weak S at the highest elevation. The Type II mintmarks are "perfect circles" with both the upper and lower loops laid out with a compass.