The Richat Structure, or Guelb er Richât (Arabic: قلب الريشات, romanized: Qalb ar-Rīšāt, Hassaniyya: [galb er.riːʃaːt] ⓘ), is a prominent circular geological feature in the Adrar Plateau of the Sahara.

Igneous rock is exposed inside and there are rhyolites and gabbros that have undergone hydrothermal alteration, and a central megabreccia.

[9] A geological expedition to Mauritania led by Théodore Monod in 1952 recorded four "crateriform or circular irregularities" (accidents cratériformes ou circulaires) in the area, Er Richât, Aouelloul (south of Chinguetti), Temimichat-Ghallaman and Tenoumer.

[10] It was initially considered to be an impact structure (as is clearly the case with the other three), but a closer study in the 1950s to 1960s suggested that it might instead have been formed by terrestrial processes.

After field and laboratory studies in the 1960s, no significant evidence was found for shock metamorphism or other deformation indicative of a hypervelocity extraterrestrial impact.

[3][4] Further analysis of deep structure underneath the surface, including with aeromagnetic and gravimetric mapping,[6] concluded that the structure is the result of ring faults which led to gabbroic ring dikes over a large intrusive body of magma, and the uplifting and later erosion of a dome, through intense hydrothermal activity through the fractured substructure.

This can form cuestas over time through the differential erosion of the resulting alternating hard and soft rock layers.

However, since these sites were first discovered by Théodore Monod in 1974,[14] mapping of artifacts within the area of the structure have found them to be generally absent in its innermost depressions.

The local apparent wealth of surface artifacts is the result of the concentration and mixing by deflation over multiple glacial-interglacial cycles.

Ridges typically consist of deeply weathered bedrock representing truncated Cenozoic paleosols that formed under tropical environments.

Numerous concordant radiocarbon dates indicate that the bulk of these sediments accumulated between 15,000 and 8,000 BP during the African humid period.

[17][18] This claim is primarily based on the concentric nature of the structure, which superficially matches Plato's description of the city.

[20][21] Skeptic Steven Novella criticised the claim, stating that the structure is inconsistent with Plato's description of Atlantis, and that the site shows no evidence of a city ever being built at the location.