The synthesis of calcite fibers has been confined to nature and is observed most prominently in sea urchin teeth and bacterial deposits. By generating a liquid-phase mineral precursor, induced by the addition of acidic macromolecules to a crystallizing solution, calcite fibers with diameters ranging from 100 to 800 nm have been deposited on existing calcite substrate crystals. A solution-precursor-solid (SPS) mechanism, which has features similar to both the vapor-liquid-solid (VLS) and solution-liquid-solid (SLS) mechanisms, is proposed as the growth mechanism. Because this aqueous-based SPS mechanism occurs under physiological conditions (and down to temperatures as low as 4 °C), it is feasible that it may be used by organisms to form their fibrous biomineral structures. This discovery suggests an interesting link between two seemingly unrelated processes, high-temperature semiconductor fiber formation and biological mineralization.