Boron Coordination Revealed in Haplogranite Glasses

A team led by Jakob Rauscher published a study clarifying how boron atoms arrange themselves within haplogranite glass structures, a key step toward understanding fractionation between silicate melts and surrounding fluids during ore-forming events.¹

The authors—Michael Fechtelkord, Sandro Jahn, Julie A.-S. Michaud, Draupadi Mothan, Melanie J. Sieber, Robert B. Trumbull, Franziska D. H. Wilke, Max Wilke, and Bernd Wunder—used solid-state nuclear magnetic resonance (NMR) spectroscopy to probe the local environment of ¹¹B and ¹⁰B in granitic glass samples with varying water content and alkali–alumina ratios.¹ Their measurements revealed distinct coordination geometries for boron, ranging from trigonal planar to tetrahedral arrangements, depending on melt composition and hydration level.¹

This finding is significant because boron's isotope fractionation—a process used by geoscientists to track magmatic‑hydrothermal evolution—is strongly influenced by its coordination state. While the behavior of boron in aqueous fluids has been well documented, little was known about how it behaves within silicate melts until now.¹ By establishing a direct link between NMR-derived coordination data and isotope partitioning, the study provides a practical framework for estimating B coordination and melt–fluid fractionation across diverse geological settings.¹