Two species of surface salt-marsh agglutinating foraminifera from sites around Britain have been investigated using SEM/EDX to examine for grain size and mineralogical selectivity of their adventitious test wall particles. Grain size and elemental measurements on test constituents of Trochammina inflata and Jadammina macrescens, from the same sites, when compared with substrate grain size distributions, suggest a high degree of grain size and mineralogical selectivity. Trochammina inflata tests are dominated by relatively small (modal class 1–3 μm) quartz grains, whereas those of J. macrescens are characterized by larger (modal class 4–9 μm) platy aluminosilicate minerals. In addition, four species of surface/subsurface agglutinating foraminifera from around Britain and Ireland were examined for mineralogical selectivity. Eggerelloides scabrus and Ammoscalaria runiana are dominated by quartz, whereas Haplophragmoides wilberti is predominantly composed of aluminosilicate minerals. Miliammina fusca does not appear to select grains by size, shape or mineralogy.