Looks pretty much like C album to me. It varies a bit in colour and amount of white powder, maybe depending on amount of sunlight, soil, moisture... Maybe if you post another picture where it looks less like C Album?
Edited to add: Oops, sorry, my poor connection was only able to open the first of your three photos, so maybe I'm wrong and the photos you posted would reveal something more different from C album.
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.