geophagy, n.
Geophagy is a practice of eating earthy substances such as clay, often to augment a mineral-deficient diet.
While most often seen in rural or preindustrial societies among pregnant women, it also occurs among children and as a psychological eating disorder. Geophagy is a type of disorder known as pica. In the southeastern United States especially tasty earth (usually a chalky earth with a certain flavor) is sold in local stores or sent to friends and family who are no longer living near the source of this earth. Geophagy was also practiced by Native Americans who would eat earth with acorns and potatoes to neutralize potentially harmful alkaloids. Clay was used in the production of acorn bread.
From Wikipedia.org