Rhizocarpon cinereovirens

Rhizocarpon cinereovirens is a species of saxicolous (rock-dwelling), crustose lichen in the family Rhizocarpaceae. This small lichen forms tiny white or pale grey crusts that seldom exceed a centimetre across, broken into minute plates with small black disc-shaped fruiting bodies. It grows on exposed, nutrient-poor siliceous rocks and metal-rich surfaces in both windswept mountain summits and coastal areas, and is found across the British Isles, Scandinavia, and northeastern United States. It is now confirmed from north-eastern China as well as the North Atlantic region of Europe and North America, giving the species a broad circumpolar–boreal distribution....read more on Wikipedia.