The domain structure of an oligoclase An16.5 deduced from satellite and main reflections in x-ray diagrams is interpreted using the theory of satellite reflections and compared with electron transmission micrographs. Electron microscopy and x-ray study allow the assumption that the entire oligoclase specimen is composed of submicroscopic domains much smaller than those known in plagioclase with peristerite texture.The intensity behaviour of the satellites indicates unit-cell-dimension modulations. The lattice modulations are assumed to correspond to an exsolution of Al-poor against Al-rich domains associated with differences in lattice parameters. These domains can be observed in the electron microscope by virtue of their diffraction contrast.X-ray and electron-microscope studies lead to the conclusion that the domain boundaries are oriented near (08[unk]); this orientation corresponds to that of the larger exsolution domains of plagioclases with the peristorite texture and is assumed in both cases to be caused by the minimalization of misfits between two structures. The domain thicknesses measured in the electron micrographs correspond to those deduced from the satellites found in the x-ray study.