A gray-white, hard, brittle metallic element. Symbol, Mn. Manganese does not occur uncombined in nature, but its minerals are widely distributed. Pyrolusite (MnO₂) and rhodochrosite (MnCO₃) are the most common minerals. The discovery of large quantities of manganese nodules on the ocean floor, containing about 24% manganese, holds promise as a source of manganese. Used to form many important alloys, esp. with steel, aluminum, and antimony; used in dry cells and glass, and in the preparation of oxygen, chlorine, and medicines.