Microbial life has refined the fine-scale chemistry of minerals for billions of years of Earth history, leaving complex, durable records of metabolic activity behind. Fracture networks in rocks preserve a durable mineral record of these ancient processes, often touching questions related to the origin and early adaptive strategies of rock-hosted, microbial life on Earth. In this project, iron-rich rocks (also high in chromium, nickel, and other metals) from Earth?s mantle, collected through scientific drilling in northern California?s Coast Range Ophiolite, are targeted for geochemical study. Fracture zones in these ~150-million-year-old rocks were hotspots of microbial activity under ancient conditions in the subsurface. This work uses an array of geochemical tools to map the chemistry of materials formed in fractures and applies a high energy x-ray-based technique (Fe K edge XANES) to define how oxidized or reduced bound iron in fracture fill minerals may be, as evidence for biogeochemical cycling of iron (for energy) in the past. Research involves collaboration with professional beamline scientists at Brookhaven National Lab and with topic expert Dr. D. Dyar of Mount Holyoke College.