The oxide precipitates (1000-6000A) were separated from as-grown CZ silicon crystal containing the swirl defects by means of chemical etching method. The selected-area electron diffraction analysis of the precipitates, which had been prepareted into the extraction replica specimens, was carried out in TEM. Simultaneously, the morphology of the swirl defects in silicon thin foil specimens was observed with TEM. Thereby, the corresponding relation between the particles in the extracrion replicas and the swirl defects in the silicon thin foils was established. It was concluded that a great number of the swirl defects are keatite (silica k) in the form of square-shaped platelets with {100} habit planes and sides in parallel with direction, and a small part of the swirl defects are a-cristobalite in the form of hexagon-shaped platelets with {111) habit planes and sides in parallel with . IR absorption spectra of as-grown CZ silicon samples showed that the square plate-shaped keatite were probably associated with the absorptior band at 1224 1/cm.