Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray solid at room temperature, and is a fairly reactive metal. Magnesium is a very important element for life, as it is used in many biological processes, including muscle and nerve function, and is also found in many minerals. Magnesium is a lightweight and strong metal, and is used in many applications, such as in the aerospace industry, in electronic devices, and in construction materials.