Magnesium and manganese are two metallic elements. Many differences exist between the two, but because of the similarity of their names, they are sometimes confused. All of the differences between magnesium and manganese stem from their separate identities as elements and the physical and chemical properties they possess as a result of their differing atomic numbers — 12 for magnesium and 25 for manganese. Both are essential nutrients, but magnesium is more important. Magnesium is also much more naturally abundant than manganese.
The appearance of the two elements is similar and, in fact, is similar to many other metallic elements. In terms of physical properties, however, there are many differences between magnesium and manganese. Magnesium is a relatively light metal that is less dense than aluminum. Manganese is approximately four and a half times as dense as magnesium and has a much higher melting point Unlike magnesium, manganese is occasionally found as a free element in nature.
Chemically, the two elements are very different. Magnesium and manganese are both metals, but belong to different groups. Magnesium is an alkali metal and is highly reactive, which means that it is never found as a free element in nature. It tarnishes in the air and reacts chemically with water in a manner similar to other alkali metals such as calcium, though much less violently. Manganese is chemically more similar to iron than to magnesium. It oxidizes readily, and it is usually found in the earth's crust as manganese dioxide, a mineral that is also called pyrolusite.
Both elements are important nutrients but serve different functions. Magnesium, although present in the human body in small amounts, is still extremely important. It is used by every major organ and metabolic system, especially in bone formation and in the heart and musculature function. Magnesium plays a role in hundreds of metabolic functions, and without it, we could not live. The human body uses magnesium to modulate levels of other minerals in the body, and it is the trigger for many enzymes which the body requires to convert food to energy. Magnesium also plays an important role in the entire ecology of the earth, as it is one of the central elements in the chlorophyll molecule, which fuels all photosynthesis in green plants.
Manganese is also an important micronutrient but in other ways than magnesium. The human body uses much less manganese than magnesium, and it has a narrower range of functions, most of which are related to metabolic functions involving carbohydrates, fats, and cholesterol, among others. It is also one component of an important enzyme that helps the body convert certain molecules to glucose, or blood sugar. Manganese is an important component in many other enzymes as well and is a component of the human body's most important natural antioxidant, which helps protect our cells from damage due to oxidation by harmful ions and free radicals.