Hydrothermal templating of mesoporous molecular sieves by nonionic triblock copolymers [poly-(oxyethylene)-poly(oxypropylene)-poly(oxyethylene)(PEO-PPO-PEO)] at specific block lengths of EO20PO70EO20 and selected 2 M HCl dosage (pH -0.3) caused the formation of micrometer-sized SBA-15 hexagons with well-ordered hexagonal pore channels (pore size and wall thickness of similar to6 nm and pore-to-pore distance of similar to12 nm) after template removal. For a beneficial lower surface energy, these {10} laterally coalesced hexagons tend to stack imperfectly over the base into towerlike entities, leaving dislocations and faults within the single domain thus formed. Evidence for the mechanism of Brownian motion/coalescence of the hexagonal-mesophase particulates, previously suggested for MCM-41 accretion in the presence of cationic surfactant, is more clearly identifiable in the present low-pH case of amphiphilic block copolymer templates and linear silica oligomers.