The Richat Structure, or Guelb er Richât (Arabic: قلب الريشات Qalb ar-Rīšāt), is a prominent circular geological feature in the Adrar Plateau of the Sahara. It is located near Ouadane in the Adrar Region of Mauritania. In the local dialect, rīšāt means feathers and it is also known locally in Arabic as tagense, referring to the circular opening of the leather pouch that is used to draw water from local wells.

It is an eroded geological dome, 40 kilometres (25 mi) in diameter, exposing sedimentary rock in layers that appear as concentric rings. Igneous rock is exposed inside and there are spectacular rhyolites and gabbros that have undergone hydrothermal alteration, and a central megabreccia. The structure is also the location of exceptional accumulations of Acheulean archaeological artifacts. It was selected as one of the first 100 geological heritage sites identified by the International Union of Geological Sciences (IUGS) to be of the highest scientific value.