People who eat chalk do so either for cultural reasons or because they have pica, which is a kind of eating disorder where people eat something other than food on a regular basis and in large quantities. Other items that people with pica will eat include balloons, metal, ashes, crayons, insects, grass, soap, sand, plastic, paint chips and baby powder.
Geophagia is the specific word to describe those with pica who eat only clay. The word pica comes from the Latin word for the magpie species. Magpies will eat almost anything. However, people that eat nonfood are more specific in their choices of what they will eat. Most people with pica, for example, will choose one particular object that they regularly eat.
Pica can be dangerous as doctors often have to operate on people who eat items such as nuts or twigs. These people can get the objects blocked within their intestines. This practice was common among slaves in the 1800s because they did not have much else to eat. Throughout the 1950s and '60s, clay-filled bags were sold for lunch at bus stops in the South.
Some people have chosen to eat clay for cultural reasons because they have been told that the clay is good for their babies during pregnancy or good for them nutritionally. Many women with pica preferences believe that they will become ill or have a miscarriage if they do not eat to eliminate their pica cravings.