Communication: Microporous ceramics and ceramic membranes have many potential applications, for example, in the chemical, environmental, energy conversion, and automotive industries. An organic template approach using sol-gel processing is described by which microporous amorphous silica is synthesized. It is shown that the very narrow pore size distribution is comparable to that of the zeolite ZSM-5 and that the membranes have ideal gas separation factors at least two orders of magnitude larger than those expected for a Knudsen diffusion separation mechanism.