Effect pigments having improved optical properties based on SiO.sub.2 flakes coated with one or more layers, where the SiO.sub.2 flakes have a thickness of from 50 nm to 150 nm; processes for the preparation thereof; and use of these pigments in cosmetics, paints, coatings, plastics, films, in security printing, in security features in documents and identity cards, for coloring seed, for coloring foods or in medicament coatings and for the preparation of pigment compositions and dry preparations; are disclosed.