Strontium

Strontium ( /ˈstrɒntiəm/ STRON-tee-əm) is a chemical element with symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and strontianite. While natural strontium is stable, the synthetic 90Sr isotope is present in radioactive fallout and has a half-life of 28.90 years.