is an alkaline earth metal that is found naturally in the minerals celestine and strontianite. Strontium shares many physical and chemical properties with calcium and barium and is highly susceptible to chemical changes.
Strontium has 16 known isotopes. Strontium that occurs naturally in the earth has four stable isotopes Sr-84, -86, -87, and -88. Twelve other strontium isotopes are unstable, meaning they are radioactive. Strontium-90 is the most prevalent radioactive isotope in the environment, although strontium-89 can be found around nuclear reactors. Strontium-85 is used in bone imaging processes by the medical field.