Iridium is one of the less common elements. Its properties are unique: hardness, chemical and corrosion resistance, capacity to maintain physical dimensions. Iridium’s high chemical inertness, including resistance to alkalis and acids (even in the concentrated state), is especially appreciated to create a protective metal layer. The iridium coating provides protection against various aggressive environments. This type of treatment is often used for aerospace parts, engine components and some types of electrical engineering parts. For example iridium is used in the production of spark plugs for automobiles.