Novel amorphous siliceous materials having shape-selective sorption properties are prepared by a novel process of (1) hydrolyzing an organosilicon compound of the formula R[Si]X.sub.3 alone or in the presence of one or more compounds either of the formula R'.sub.n MY.sub.m, wherein R and R' are non-hydrolyzable organic groups, X is a hydrolyzable group, Y is the same as X or oxygen, [Si] is silicon or ##STR1## M is metal or non-metal, including silicon, of any group of the Periodic Table other than IA, IIA, VIIA or O, m is a number over 0 and up to 8 and n is 0 or a number less than 8, or an inorganic compound consisting of an anionic portion made up of M and Y and a cationic portion of either hydrogen, alkali or alkaline earth metal or ammonium; (2) effecting condensation polymerization of the hydrolyzed product; and (3) calcining the resulting polymerized product to convert all the R and R' groups to hydroxy or hydrogen. Pore size distribution of the final composition is primarily controlled by appropriate selection of the R group of the R[Si]X.sub.3 precursor. The amorphous synthetic solids of this invention are useful in such conversion processes as shape-selective cracking, hydrocracking, hydrogenation-dehydrogenation, oxidation, and methanation processes. They are also useful as sorbents and catalyst supports.