The Richat Structure, also known as the Eye of the Sahara and Guelb er Richat, is a prominent circular feature in the Sahara desert of west- central Mauritania near Ouadane. This structure is a deeply erode, slightly elliptical, 40 km in diameter, dome.
The sedimentary rock exposed in this dome ranges in age from Late Proterozoic within the center of the dome to Ordovician sandstone around its edges. The sedimentary rock comprising this structure dip outward at 10°–20°. Differential erosion of resistant layers of quatzite has created high-relief circular Ceustas. Its center consists of a siliceous breccia covering an area that is at least 3 km in diameter.