The craving for chalk is most likely related to iron deficiency. The general medical term for craving certain items is "pica." With iron deficiency, you can have cravings other than chalk, including ice, paper, coffee grains and seeds. Its not known why iron deficiency causes pica. But once a person has replenished his or her iron stores, the craving disappears.
Women, especially pregnant women, commonly have iron deficiency anemia. So this problem is seen most often in women.
The usual treatment for iron deficiency is iron sulfate. But iron can be constipating. So I recommend that people start with 1 tablet per day. Each dose is 325 milligrams. If possible, try to increase it to one tablet twice per day. Three times per day would be ideal.
In addition to constipation, some people find that iron sulfate irritates their stomach causing upper abdominal discomfort. If that becomes a problem, you can switch to iron gluconate at the same doses. In general, less iron gets into the body with iron gluconate compared to iron sulfate.
One more thing you can expect very dark (even black) stools from iron.