Explanations for the well-established relationship between mining and conflict interpret violence near resource extraction sites as part of conflict over territory or government. We provide evidence that competition between artisanal and industrial miners is also an important source of natural resources related conflict, from qualitative case studies at mining sites in the Democratic Republic of Congo and Zimbabwe and a large-N analysis. For the latter, we use machine learning to estimate the feasibility of artisanal mining across the continent of Africa based on geological conditions. We find the impact of price shocks on violent conflict is roughly three times as large in locations with industrial mining where artisanal mining is feasible as it is in places with industrial mining but no potential for artisanal mining. Back-of-the-envelope calculations suggest that 31 to 55% of the observed mining-conflict relationship is due to violent industrial-artisanal miner competition. This implies new avenues for conflict-mitigation.