[{"Bold_text": "noun", "List Items": ["a silver-white divalent metal, occurring combined in limestone, chalk, gypsum, etc., occurring also in vertebrates and other animals, as a component of bone, skeletal mass, shell, etc., and as a necessary element in nerve conduction, heartbeat, muscle contraction, and many other physiological functions.:Ca;:40.08;:20;:1.55 at 20°C."]}]