Potassium chloride (KCl) is a metal halide salt composed of potassium and chloride. It occurs naturally as the mineral sylvite and in combination with sodium chloride as sylvinite. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water and its solutions have a salt-like taste. KCl is used in food processing as a sodium-free substitute for table salt for persons concerned about the health effects of sodium, fertilizer production, medicine and other scientific applications such as in water as a completion fluid in petroleum and natural gas operations, as well as being an alternative to sodium chloride in household water softener units. Solutions of KCl are common standards, for calibration of the electrical conductivity of ionic solutions, since KCl solutions are stable, allowing for reproducible measurements. In aqueous solution, it is essentially fully ionized into solvated K+ and Cl– ions.