Laboriously extracted from rock, lapis lazuli was brought with difficulty and danger from Afghanistan and Persia to provide a rich blue, known sometimes as azure, or ultramarine (i.e. beyond the sea, where the lapis came from), for scribes and painters of illuminated MSS. Its value was indicated by being used only for significant parts of an image, e.g. the blue of the Virgin's cloak. [< Lat. lapis = stone + lazuli < Persian lazward = lapis lazuli] -
Cf. Cinnabar
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.