Bromine is the twenty-fifth element in order of abundance in Nature. It is so chemically active that it never occurs free in Nature, but always found as a halide. Except for same rather rare silver salts, no natural mineral contains bromine as an essential constituent. There are salt deposits or brines in various parts of the world where bromine has been concentrated by evaporation of water from prehistoric seas or salt lakes. Average ocean water contains 67 mg of bromine per liter, and is the major source of this element. The major world producers of bromine are the United States, Israel and Germany.