Cobalt is a relatively rare element of the earth's crust. It is a hard ferromagnetic, silver-white, hard, lustrous, brittle element. The element is active chemically, forming many compounds. Cobalt is stable in air and unaffected by water but is slowly attacked by dilute acids. It is used in many alloys, in magnets and magnetic recording media, as catalysts for the petroleum and chemical industries, and as drying agents for paints and inks.