The mineral essential for forming red blood cells is iron. Iron plays a crucial role in the production of hemoglobin, the protein in red blood cells that binds to oxygen and transports it throughout the body. Adequate levels of iron are necessary for maintaining healthy blood and efficient oxygen delivery to tissues and organs. Iron deficiency can lead to anemia, characterized by fatigue, weakness, and decreased immunity. Food sources rich in iron include red meat, poultry, fish, beans, lentils, spinach, and fortified cereals. It's important to maintain a balanced diet to ensure sufficient iron intake.