Iron Biomineralization

Abstract

During the last two decades, the number of minerals identified as biological precipitates increased fourfold, from the 10 known in 1963 (Lowenstam, 1963) to over 40 (Lowenstam and Weiner, 1983) recognized today. And yet, from the continuing rate of discovery, it is quite clear that many more probably remain to be recognized. Among the minerals which have been discovered and for which the crystal structure has been clarified with modern techniques are 10 iron minerals, including oxides, sulfates, sulfides, and phosphates. Table I’lists these minerals and their distribution among the phyla, biomineralization modes, and known functions. Several of these minerals are known to have a wide distribution among prokaryotes and eukaryotes, and two of them (ferrihydrite and magnetite) are likely to be the fourth and fifth most widely utilized biomineralization products in present-day organisms. Ferrihydrite (2.5Fe2O3 · 4.5H20) forms the core component (micelle) of the iron storage protein ferritin in numerous animal classes, and related ferric oxide minerals occur in ferritin like structures in other eukaryotes as well as in some prokaryotes (e.g., phytoferritin and bacterioferritin). Less than 25 years ago, magnetite had been identified in chitons (class Polyplacophora; Lowenstam, 1962a), but its biogenic origin was regarded with great skepticism. As shown by the papers in this volume, however, the phyletic distribution of magnetite may soon compete in abundance with ferrihydrite for fourth place.