hmm not sure they are the same things. They may be produced by a similar process, but don't seem to result in the clam-shell look we are talking about here.Somewhere in North Wales
Of course, there are bateria's that eat iron. This is what they are whitnessing with the Titanic. It should be intact due to low oxygen levels but is slowly being eaten away. THe bacteria seem to leave something similar to that on the chain in your photo.