The three-dimensional particle size and shape of mechanically delaminated talc thin platelets were determined by combining two different methods. The plate diameter was determined by microscopy with the aid of an image analyser and the thickness from the X-ray crystalline size perpendicular to the basal plane. The net line broadening of the X-ray diffraction peak, necessary for the determination of X-ray crystallite size, was evaluated by electron microscopy. In order to correct X-ray diffractometry for instrumental broadening, the platelet thickness of a representative specimen was obtained directly using a transmission electron microscope coupled with a laborious slice technique with an ultramicrotome.