Is this an error?

[enworb]

Very good pictures nancy. The difference i see between say the 2008 5c double rim and the $1 coins is that the double ring is present on UNC coins but on $1 coins it is not. Its almost as if it develops which leads me to think the $1 coins are PMD. I think your coins and the 2008 5c must have something to do with the die.

[Fulvio]

Great closeup! It almost looks like the metal has been chiselled away with a really tiny pick. A couple of things to note.... These type of rings are different to the previously discussed sort, which don't seem to exhibit these marks. Both of these coins, as well as the ones I've seen of this type, have doubling as well, whereas the smooth variety do not. And as for die damage, we can rule that out, as the rings would be raised if that were the case.

Whatever caused this has to do with the planchet rather than the die I think. Stress fractures perhaps?