Hi, I understand your concern. The chalk-eating is also called Pica disorder. It is often noted in anemic people. Get a CBC done to check it out. Iron supplements will help with anemia and stop chalk eating. Next, intestinal worms can cause anemia. Stool examination will confirm it for a more adequate treatment. If no anemia, and no parasites, psychological problems should be also examined further by psychologist. Chalk eating can be harmful. Chalk is a limestone and contains high amounts of calcium carbonate. If taken in excessiveness, it might cause kidney stones. Goitre (goiter is the correct spelling) is the enlarged thyroid gland associated with low iodine levels. Chalk craving cannot lead to goiter. All the best.