Ultramarine is a blue pigment consisting primarily of a double silicate of aluminium and sodium with some sulfides or sulfates, and occurring in nature as a proximate component of lapis lazuli. Ultramarine is the most complex of the mineral pigments, a complex sulfur-containing sodio-silicate (Na8-10Al6Si6O24S2-4). Some chloride is often present in the crystal lattice as well. The blue color of the pigment is due to the S3− radical anion, which contains an unpaired electron.

Ultramarine blue is commonly used by many types of contemporary painting.