Hierarchical self-organization of framboidal pyrite enables biosignature preservation

Framboidal pyrite serves as a critical archive of mineralization and paleoenvironmental history, yet its formation remains contested between biological templating and abiotic self-organization. Integrating geometric and crystallographic analyses of framboidal pyrite from the Gakkel Ridge, we reveal a hierarchical architecture defined by fractal geometry (fractal dimensions of 1.7–1.9) and systematic core-to-rim gradients in crystallinity and lattice strain. These findings underpin a unified three-stage growth model: initiation by synchronous nucleation, advancement via diffusion-limited aggregation into a fractal skeleton, and finalization through surface-energy minimization driving spheroidization. This mechanism provides a universal abiotic explanation for framboidal formation across diverse mineral systems. While biological activity may provide the initial supersaturation pulse, the characteristic texture remains a robust outcome of physical forces. The resulting architecture optimizes biosignature preservation, wherein defect-rich cores adsorb organic matter encapsulated by high-crystallinity rims. These findings resolve the long-standing biotic-abiotic dichotomy, establishing framboids as physically inevitable products and robust geochemical proxies for decoding mineralogical biosignatures in both terrestrial and extraterrestrial contexts. Microscopic and spectroscopic observations of framboidal pyrite from the Gakkel Ridge support a 3-stage growth model, which is compatible with, but does not require, biological activity and can explain the preservation of biosignatures in framboidal structures