Richat Structure, Rock formation on the Adrar Plateau, Mauritania

The Richat Structure, also called the Eye of the Sahara, is a large circular rock formation on the Adrar Plateau in Mauritania. It is made of concentric rings of sedimentary rock, quartzite, and limestone that differ in color and texture, forming a layered pattern clearly visible from above.

The structure was first described in the 1930s and 1940s as the Richât Crater or Richât buttonhole, and Richard-Molard in 1948 attributed it to a laccolithic uplift. A geological expedition led by Théodore Monod in 1952 recorded four circular irregularities in the area, including Er Richât. Coesite reported in samples was reidentified as barite in 1969, and Matton et al. (2005, 2008) concluded it was not an impact structure.

In Hassaniya Arabic the name rīšāt means feathers, and locals also call the structure tagense, after the round opening of the leather pouch used to draw water from wells. Astronauts on Shuttle missions used the rings as a landmark for orientation from orbit.

The nearest town is Ouadane, and reaching the site requires a vehicle suited to desert terrain and enough water for the trip, since no paved roads lead there. A GPS device is necessary because the open sand plains have no marked trails to follow.

At the very center lies a megabreccia core, a mass of broken rock fragments pointing to very ancient geological forces that acted deep below the surface. Astronauts have used this formation for decades as a training reference for recognizing surface structures from orbit, since it stands out clearly against the surrounding desert floor.