Calcium and magnesium are the two most common alkaline earth metals. These are two of the six elements that are classified as alkaline earth metals and are found in the Earth's crust.
Calcium and magnesium are also elements that are important to human life. Magnesium is vital in the formation of chlorophyll, which is essential for photosynthesis. Calcium is important to human health. It makes bones and teeth stronger and helps to regulate blood pressure and heart beat. Calcium also assists with blood clotting. Both of these elements are found in rock form rather than elemental form due to being highly reactive.