Significance In the absence of light, biomass production is driven by chemical energy through microbial chemosynthesis. H ₂ , a potent reductant capable of supporting chemosynthesis, is readily generated by reactions between iron and silicate minerals and water. Here, we show that lithogenic H ₂ produced by glacial comminution of iron- and silica-rich basaltic bedrock supports microbial chemosynthesis. Lithogenic production of H ₂ in cold, dark subglacial environments and its use to generate chemosynthetic biomass suggest the potential for subglacial habitats to serve as refugia for microbial communities in the absence of sunlight, such as during Snowball Earth episodes or on icy planets where photosynthesis may not yet have evolved or where light is restricted.