Three allotropic forms of the metal exist, with transition points at 235 and 540C. Strontium is softer than calcium and decomposes water more vigorously. It does not absorb nitrogen below 380C. It should be kept under kerosene to prevent oxidation. Freshly cut strontium has a silvery appearance, but rapidly turns a yellowish color with the formation of the oxide. The finely divided metal ignites spontaneously in air. Volatile strontium salts impart a beautiful crimson color to flames, and these salts are used in pyrotechnics and in the production of flares.
Natural strontium is a mixture of four stable isotopes.
Sixteen other unstable isotopes are known to exist. Of greatest importance is 90Sr with a half-life of 29 years. It is a product of nuclear fallout and presents a health problem. The major use for strontium at present is in producing glass for color television picture tubes. It has also found use in producing ferrite magnets and in refining zinc.