In this paper I explore what we can do with minerals as scholars of the human. To stay with their ambivalence, between ecological destruction and technological development, it might be worth thinking again about how humans are entangled with minerals. Here, I build on the observation that minerals make both our environment and our very selves; and I engage with debates around materiality to explore what this feature can do for us in one particular case: lithium. Through lithium I explore how minerals confront us with complex epistemological issues in interdisciplinary conversations. Based on science studies and work on scale I seek ways between social constructivism and scientific universalism, suggesting matters of scale as a way forward. Drawing on diverse histories of science, technology and medicine I perform matters of scale by telling a pragmatic story about lithium as specific material situated in scientific practice.