Sedimentary microbial communities play a critical role in the global carbon cycle, oxidizing deposited organic carbon and thus influencing the type of carbon buried from Earth’s surface. The rate of microbial metabolism within sedimentary microbial communities is often linked to the lability and amount of organic carbon deposited. Here we show that, in pure culture, for sulfate-reducing bacteria (Desulfovibrio bizertensis) the rate of microbial sulfate reduction is a function of the proportion of clay minerals present in the incubation vials. We argue that the presence of clay minerals stimulates the growth of the sulfatereducing bacteria and the rate at which sulfate is consumed; we conclude that this is not linked to nutrients and carbon on the clay minerals but rather is a function of the high specific surface area of clay minerals. We further use a global compilation of sedimentary pore fluid data to demonstrate that these observations can be seen in marine sediments, that is pore fluid sulfate concentration gradients in marine sediments correlate with the percentage of clay minerals in the sediment. Our findings suggest that sediment mineralogy influences the rate of microbial activity in marine sediments, which has heretofore not been considered.