MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Grey limestone and iron oxide, close-up. This calcarerous sedimentary rock has an oolithic texture that is not easily visible. The grey colour comes from very fine iron sulphide (pyrite) crystals, produced in a reducing environment. Iron oxidation by oxygen-rich water may change the colour to reddish-orange, as seen here down centre. This specimen is part of the Geoscope geological park, located between Les Monts-Vert and Albaret-Sainte-Marie, central France.
Model release not required. Property release not required.