Mineral Structure Solved

Ferrihydrite is a naturally occurring iron oxide and is produced commercially to scavenge heavy metals from wastewater. But there has been no consensus on ferrihydrite's formula or structure because its nanosized crystallites have foiled traditional structure determination methods. Now, geochemists F. Marc Michel, Martin A. A. Schoonen, and John B. Parise at the State University of New York, Stony Brook, and colleagues propose a new atomic model for ferrihydrite (Science, DOI: 10.1126/science.1142525.) They collected X-ray scattering data at a synchrotron source, then analyzed the data with an atomic pair distribution function method. The researchers determined that in its ideal form, ferrihydrite has the formula Fe₁₀O₁₄(OH)₂ and consists of 20% FeO₄ tetrahedra (shown in red, with oxygen in blue) and 80% FeO₆ octahedra. "The work represents a major leap forward in understanding this important mineral," says chemist R. Lee Penn of the University of Minnesota in an accompanying Science commentary.