Study in rust and lichen

I've walked past this abandoned iron rail in the bed of a disused rail line many times before without looking closely. Today I got down on hands and knees and found this lovely patterning. I was amazed to find the lichen growing directly on the rusted metal. I think it is one of the Lecidea species and I know some of these are found on metal-rich rocks. However, at the moment I have not been able to track down much in the literature about rusted iron as a substrate. More research to be done.