The present invention relates to pigments, the particles of which generally have a length of from 2 .mu.m to 5 mm, a width of from 2 .mu.m to 2 mm, and a thickness of from 20 nm to 2 .mu.m, and a ratio of length to thickness of at least 2:1, wherein the particles contain a core of SiO.sub.y with 0.70.ltoreq.y.ltoreq.1.8, especially 1.40.ltoreq.y.ltoreq.1.8, having two substantially parallel faces, the distance between which is the shortest axis of the core, comprising (a) a material, especially a metal oxide, having a high index of refraction; or (a) a thin semi-transparent metal layer; a process for their production and their use in paints, ink-jet printing, for dyeing textiles, for pigmenting coatings (paints), printing inks, plastics, cosmetics, glazes for ceramics and glass.