Measurement of thickness of dispersed clay flakes with the electron microscope

The shadow lengths of dispersed flakes of the layer-lattice mineral, allevardite, were measured with the electron microscope. Details of the experimental technique are given, and the importance of using samples free from very small material is stressed. Measurements of flake thickness made in this way agree well with estimates of the basal spacing of the collapsed lattice obtained from X-ray diffraction, and dispersion of allevardite was found to produce suspended flakes 19 Å thick, corresponding in thickness to the basic structural unit of two 2:1 layers.