Small-angle x-ray scattering has been used in an investigation of the pore structure of “sivol,” a material prepared by thermochemical treatment of chrysotile asbestos. It has been shown that sivol has a well-developed pore structure. Pore size distribution curves have been obtained, showing a maximum with a radius of gyration R=2.5–3.0 nm. The data from small-angle scattering are in good agreement with results obtained in previous calculations based on adsorption measurements (for R ≥ 2.5 nm). It has been shown that some of the finest pores are not accessible for the molecules being adsorbed.