<p>Limpets, marine mollusks that feed on algae by scraping rocks, have evolved teeth renowned as among the strongest biological materials known. These teeth are iron-based biocomposites, primarily consisting of goethite nanorods embedded within a silica-rich matrix. A central mystery has been how limpets produce goethite—a mineral that typically requires extreme synthetic conditions—under ambient physiological settings. Here, we combined transcriptomics and functional assays to investigate the teeth of the limpet <i>Cellana toreuma</i>. RNA-seq in compartmented regions of teeth found differential gene expression for teeth formation involving intensive chitin metabolism and redox reaction. Through RNA interference, we demonstrated that a specific limpet-derived ferritin is essential for tooth iron accumulation and mineralization in vivo. We further identified and characterized this ferritin, showing its ability to bind Fe²⁺ and promote iron mineralization both in vitro and ex vivo. These findings provide direct evidence supporting the hypothesis that limpets form goethite through in situ oxidation of Fe²⁺. This work advances our understanding of limpet tooth microstructure and iron biomineralization mechanisms, offering valuable insights for the design of biomimetic wear-resistant materials under ambient conditions.</p>