It is true that the form of calcium in eggshells is calcium carbonate, but there is a significant difference between the calcium carbonate from eggshells and calcium carbonate mined from the ground. The ultra-pure calcium from eggshells exists in a matrix. This matrix consists of trace minerals important to maintain bone health. These trace minerals contain boron, strontium, and phosphorus among others. More importantly, the matrix includes natural transport proteins that help calcium absorption in the body. This natural matrix of the eggshell results in a highly absorbable calcium. Calcium carbonate that is mined from the ground is completely devoid of these additional important nutrients.