In order to obtain a preparation for checking the validity of the Kelvin equation for capillary condensation in cylindrical tubes of very small diameter, and the Wash-burn equation for mercury penetration in such tubes, the structure and texture of chrysotile and garnirite were studied by electron microscopy. A method is indicated by which the internal pore size distribution in such preparations can be calculated. Garnirite is less suitable for the purpose, owing to unusual crystal growth and the occurrence of growth defects, but it lends itself excellently for visualizing by means of electron microscopy the layer structure of the walls of the hollow needles which form the crystallites in these asbestoslike silicates. The distance between the layers as established from electron microscopy is in rather good accordance with the distance determined crystallographically. Pore size distributions are presented of chrysotile preparations as calculated from electron microscopy. In forthcoming publications these will be compared with distributions found from nitrogen capillary condensation and mercury porosimetry.