Indium is a chemical element with symbol In and atomic number 49. It is a post-transition metallic element that is rare in Earth's crust. The metal is very soft, malleable and easily fusible, with a melting point higher than sodium, but lower than lithium or tin. Chemically, indium is similar to gallium and thallium, and it is largely intermediate between the two in terms of its properties. It has no obvious role in biological processes and common compounds are not toxic. It is most notably used in low melting point metal alloys such as solders, in soft metal high vacuum seals, and in the production of transparent conductive coatings of indium tin oxide (ITO) on glass.