The mesostructure of porous minerals grown by surfactant-templated processes is today well established.([1]) Sol-gel synthesis in surfactant templates usually involves a subtle balance of cooperative thermodynamic and kinetic mechanisms. Although not yet clearly understood, the mesoscale texturing can be well controlled empirically, and various mesoporous structures have been observed with different symmetries and porosities.([2]) Free bulk-mineral growth generally leads to microparticles with random-shapes.([3]) Morphology of the particles results from a complex interplay between reaction-diffusion mechanisms, elasticity, and interfacial and topological constraints of the surfactant mesophase. To achieve both a higher degree of control and a hierarchically organized structure, mineralization can be confined at a macroscopic interface and can be used to grow hollow spheres or core-shell particles by various methods.([4]) In this context, Schacht et al. have used oil-water interfaces of oil droplets in water (direct emulsions) to produce spherical mesoporous capsules filled with oil.([5]) The mineral precursors, initially dissolved in the oil droplets, condense after hydrolysis at the oil-water interface. The continuous water phase contains a single water-soluble surfactant that governs the mineral mesoporosity and stabilizes the droplets against coalescence.([6]) The obtained systems are of great interest as hierarchically organized minerals with potential encapsulation applications. Nevertheless, in direct emulsions mineralization takes place within the bulk continuous phase. The absence of confinement makes the control of diffusion mechanisms and particle shapes difficult, as these can also be affected by the hydrodynamic flow.([2,3,5]) In this paper we use reverse emulsions, instead of direct ones, where mineralization takes place only within the droplets, which act as model, microreactors. This allows more controlled conditions and helps in providing insights on cooperative silica/surfactant growth mechanisms. Indeed, in our case, the flux of mineral precursors is limited by their diffusion in the viscous continuous phase and penetration throughout the surface area of the droplets. As diffusion in the aqueous phase is much faster, our systems can be viewed as microreactors where the concentration of one reactant is progressively increasing as time elapses. Observing this system as a function of time, as well as the resultant systems, reveals that mineralization takes place only above a well-defined hydrolyzed precursor concentration within the droplets. This behavior suggests that the system reaches a phase boundary, corresponding to the formation of a mesophase made of silica oligomers and surfactants, prior to mineralization.