The present invention relates to plane-parallel structures of silicon/silicon oxide (silicon/silicon oxide flakes), obtainable by heating plane-parallel structures of SiO.sub.y in an oxygen-free atmosphere at a temperature above 400.degree. C., wherein 0.70.ltoreq.y.ltoreq.1.8, or plane-parallel structures of silicon/silicon oxide, obtainable by heating plane-parallel structures of SiO.sub.x in an oxygen-free atmosphere at a temperature above 400.degree. C., wherein 0.03.ltoreq.x.ltoreq.0.95, a process for their production and their use for the production of interference pigments.