Visualization of the hollowness in unit particles of allophane and imogolite

Allophane and imogolite were negatively stained with LaCl₃ and examined in an electron microscope. Many white spots having a diameter of 20 to 25 Å and white striatums having a width of 8 to 10 Å appeared against dark background in the micrographs of allophane and imogolite, respectively. This is taken as an evidence of the presence of the hollow in the unit particles of allophane and fibrous structural units of imogolite. In some micrographs unit particles of allophane appeared to have thicker and electron denser wall. This is interpreted in terms of positive staining through simultaneous adsorption of La³⁺ and CI^- ions.