Manganese

Not to be confused with Magnesium.
Manganese is a chemical element (atomic number 25). Although a metal in its pure state, it is very reactive and is never found as such in nature. In the human body, it is a necessary trace element in many enzymes. However, in large quantities, it is toxic to nerves. The daily requirement is measured in micrograms (thousandths of a gram) and is readily found in plants where it plays a role in photosynthesis. 
Manganese at WikipediaCategory:Chemistry