Large igneous provinces (LIPs) famously host voluminous lava flows and large intrusive magma bodies that feed surface magmatism. However, they often also include substantial components of fragmental volcanic rocks. These fragmental rocks result from diverse processes including fire fountaining at fissures, phreatomagmatic interactions with subsurface fluids, and lava-water interactions. Pyroclastic fire fountaining and phreatomagmatic activity can generate buoyant eruption columns, modulating the altitude of gas injection. Both phreatomagmatic and lava-water activity can produce large volumes of permeable, glass-rich, mafic volcaniclastic material. These mafic volcaniclastic deposits (MVDs) are prone to reaction and alteration. Here, we review the role of mafic volcaniclastic rocks in LIPs, and consider the chemical fluxes and environmental consequences of mafic volcaniclastic alteration across a range of timescales. We suggest that release of phosphorus, nickel, and iron during emplacement and alteration of LIP mafic volcaniclastic deposits merits further investigation as a mechanism by which LIPs impact marine chemistry and productivity.