Geologically, Suilven is formed of Torridonian sandstone, sitting on a landscape of Lewisian Gneiss. The surrounding rocks were eroded during an episode of glaciation. Suilven was covered by the last British and Irish Ice Sheet. Prior research described Suilven and many other mountains in Northwest Scotland as nunataks, but cosmogenic isotope dating of mountaintop erratics has since disproved this hypothesis. The flow of ice created the distinctive narrow teardrop plan, while carving and scouring the vertical sides of the mountain.