Stromatoporidos.Dev.Baztan.Navarra.jpg

What's with the blue?

I can`t understand you! Ha,ha! :-) Well, I tried to take a pic with some different coloured backwars; I was triying to enhace the details, but I was wrong! It seems to be all blue! The actual slate is light metallic grey, with some orange-reddish iron stain. The brachiopods are at right side of it.