Calcium carbonate is one of the common substances in nature. It is found under the most varied forms, both in the mineral as in plant and animal kingdom. In the more or less pure form constitutes the marble, granite etc. It forms the shellfish´s shell and the animals’ skeleton. Insoluble in pure water and alcohol; it dissolves in saturated water with carbon acid. The medicine is prepared by grinding the medium cover of the oyster shell, where Hahnemann thought to find calcium carbonate perfectly pure.