Sea salt crystals, differential interference contrast light micrograph. Sea salt is a coarse (large-grained) type formed naturally by the evaporation of sea water. It is primarily sodium chloride, but unlike purer forms of that salt it contains traces of elements like zinc, magnesium, iron, calcium, potassium, manganese and iodine. This gives sea salts a distinctive taste. Magnification: x25 when printed at 10 centimetres wide.