Background – Diatoms are unicellular algae, prolific in nearly all aqueous environments on earth. They are encased between two siliceous valves that each feature a variety of intricately patterned species-specific siliceous structures. How diatoms use biological and physical processes to form these tiny detailed structures is largely unknown. This work is concerned with the smallest regular structures in diatom valves, the pore occlusions, and the processes involved in their formation. Theory and method – We developed a discrete, free-boundary, reaction-diffusion computer model to assess a new physically motivated hypothesis: pore occlusion patterns in the genus Achnanthes are simply expressions of silica diffusion and deposition within a pore covered by a membrane (silicalemma), whose deformation interacts with the growth of the pore boundary to control the silica influx. Preliminary results and discussion – Simulations generate some promising pore features such as bifurcating and curved protrusions that grow towards one another, as seen in diatom pore occlusions. But they tend to be irregular and, to date, taking into account of smoothing and regularizing effects only partially symmetrized formations. Potential future work on this point is outlined.