Wikipedia, says it's in baby formula, though after reading the lines prior, I was surprised:
Magnesium chloride is used for a variety of other applications besides the production of magnesium: the manufacture of textiles, paper, fireproofing agents, cements and refrigeration brine, and dust and erosion control. Mixed with hydrated magnesium oxide, magnesium chloride forms a hard material called Sorel cement.
Magnesium ion Mg2+ (usually added as the chloride) is an important component in the polymerase chain reaction, a procedure used to amplify DNA fragments. It is generally used in experimental biology whenever RNA and DNA and their enzymes are to function in vitro, since Mg2+ is a necessary associate ion for nucleotides in biology, such as ATP.
Magnesium chloride is also used in several medical and topical (skin related) applications. It has been used in pills as supplemental sources of magnesium, where it serves as a soluble compound which is not as laxative as magnesium sulfate, and more bioavailable than magnesium hydroxide and magnesium oxide, since it does not require stomach acid to produce soluble Mg2+ ion. It can also be used as an effective anaesthetic for cephalopods, some species of crustaceans, and several species of bivalve, including oysters.
Magnesium chloride (E511) is an important coagulant used in the preparation of tofu from soy milk. In Japan it is sold as nigari (にがり, derived from the Japanese word for "bitter"), a white powder produced from seawater after the sodium chloride has been removed, and the water evaporated. In China it is called lushui (卤水). Nigari or lushui consists mostly of magnesium chloride, with some magnesium sulfate and other trace elements. It is also an ingredient in baby formula milk.
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