Minerals exist in three categories with respect to absorption rate into the human body at the cellular level, also known as bioavailability. Mineral absorption rates decrease in humans as we age. The most common but least absorbable form is the metallic mineral. Minerals in metallic form also possess a positive electrical charge. Iron oxide, or rust, is one way the metallic mineral, iron, occurs in nature.
Limestone contains calcium.
In the 1960's, chelated minerals became available. Scientist learned that by attaching an enzyme, such as an amino acid, to the clay or metallic form of a mineral they could increase the absorption rate of that mineral. Although chelated minerals are more expensive than their basic, metallic counter parts, their bioavailability is 4 to 5 times more than that of the basic mineral. Colloids are the third category of minerals. Colloidal minerals are different in many respects from the previously discussed minerals.