The Richat Structure, also known as the Eye of the Sahara and Guelb er Richat, is a prominent circular feature in the Sahara near Ouadane, west–central Mauritania. The Richat Structure is a deeply eroded, slightly elliptical dome with a diameter of 40 kilometres (25 mi). 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. Initially interpreted as an asteroid impact structure because of its high degree of circularity, the Richat Structure is now regarded by geologists as a highly symmetrical and deeply eroded geologic dome. After extensive field and laboratory studies, no credible evidence has been found for shock metamorphism or any type of deformation indicative of a hypervelocity extraterrestrial impact. A more recent multianalytical study on the Richat megabreccias concluded that carbonates within the silica-rich megabreccias were created by low-temperature hydrothermal waters, and that the structure requires special protection and further investigation of its origin.