Surging demand and dizzying price hikes have raised concerns that inadequate metal and mineral supplies may impede the clean energy transition. Given the urgency of reducing fossil fuel use, the science and policy worlds must solve two main challenges: how to ensure the availability and affordability of critical metals in the quantities needed, and how to manage the environmental impacts related to mining and processing them. The latter issue is likely to be much trickier than the former, argue Henry Lee and Xin Sun.