Strontium is an element of the alkaline earth family of metals. It has the atomic symbol Sr, atomic number 38, and atomic weight 87.62. Strontium is a bright silvery metal that is softer than calcium and even more reactive in water, which strontium decomposes on contact to produce strontium hydroxide and hydrogen gas. It burns in air to produce both strontium oxide and strontium nitride, but since it does not react with nitrogen below 380 �C it will only form the oxide spontaneously at room temperature. It should be kept under kerosene to prevent oxidation freshly exposed strontium metal rapidly turns a yellowish color with the formation of the oxide. Finely powdered strontium metal will ignite spontaneously in air. Volatile strontium salts impart a crimson color to flames, and these salts are used in pyrotechnics and in the production of flares. Strontium presents a health problem since it substitutes for calcium in bone, preventing expulsion from the body.