Ultramarine is a blue pigment consisting primarily of a double silicate of aluminium and sodium with some sulphides or sulfates, and occurring in nature as a proximate component of lapis lazuli. The pigment colour code is P. Blue 29 77007. Ultramarine is the most complex of the mineral pigments, a complex sulfur-containing sodio-silicate (Na8-10Al6Si6O24S2-4) containing a blue cubic mineral called lazurite (the major component in lapis lazuli). Some chloride is often present in the crystal lattice as well. The blue colour of the pigment is due to the S3− radical anion, which contains an unpaired electron.