From several investigations it is known that magnesium oxide or hydroxide therapy causes a considerable delay of kidney stone recurrence in man. Further, it is known that the mortality of populations due to cardiovascular disease in areas with hard drinking water containing more magnesium and having a higher Mg/Ca ratio than soft water, is considerably lower than in soft water areas. In the present study a physiological model for the homeostasis of calcium and phosphate is given. It is shown that and why a slight magnesium deficiency causes the pH of bone extracellular fluid to decrease at or below the pH level of the other body fluids. This decrease makes the other body fluids supersaturated with octocalcium phosphate and this is the prime reason for calcification disorders in the soft tissues. Therefore, the hypothesis is proposed that soft tissue calcifications can be stopped and even prevented by magnesium therapy. However, they are not reversible and treatment with chelate therapy is contraindicated.