Magnesium chloride. Polarised light micrograph (LM) of crystals of magnesium chloride (MgCl2). Typically, magnesium chloride forms complexes with other molecules; the hygroscopic hexahydrate MgCl2.6H2O is used in moistening cotton threads in spinning and with hydrated magnesium oxide it forms a hard material called Sorel cement. Magnesium chloride is also used as a de-icer on highways throughout the United States. Magnesium (Mg) is an alkaline earth metal, silver white and very light, and may be obtained by electrolysis of magnesium chloride.