Strain energy-driven grain growth in quartz aggregates: Implications for microstructural evolution and recovery

Grain growth in quartz aggregates is traditionally understood as a surface energy driven process, where larger grains grow at the expense of smaller ones in order to reduce the total grain surface area. However, most studies that contributed to this concept used relatively homogeneous, fine-grained quartz aggregates, which may not precisely reflect natural samples. Here, we performed an isotropic hot-pressing experiment using a coarser-grained quartz powder with grain sizes between 64 and 125 μm. The experiment was carried out using a Griggs-type solid-medium apparatus at controlled conditions of 1 GPa, ∼950 °C, and hot-pressing duration of ∼8 h. A thermal gradient across the sample produced progressive microstructural variations, reflecting differing intensities of recovery overprint interpreted as distinct evolutionary stages. EBSD analysis revealed that relatively smaller grains with low internal misorientation (i.e., low dislocation density), grew at the expense of both smaller and larger grains with higher misorientation (i.e., higher dislocation density). Grain boundary density remained constant throughout the microstructural evolution, suggesting that the stored strain energy of the system was reduced without reducing surface energy. Interestingly, the strain energy driving force was sufficient to mobilize—and ultimately eliminate—typically more stable low-angle boundaries between growing and consumed small grains. These findings challenge the conventional grain growth models, demonstrating that local strain energy differences can dominate microstructural evolution under static conditions, overriding surface energy as the primary driving force. This has implications for interpreting annealed quartz microstructures in natural rocks and raises caution for direct use of recrystallized grain size as a paleo-stress proxy in rocks that underwent static recovery after deformation. • Strain energy gradient can override the surface energy-driven grain growth in quartz. • Small strain-free grains grow at the expense of larger, strained ones. • Total grain surface remains constant during the strain energy equilibration. • Typically more stable low-angle boundaries can migrate due to strain energy gradient. • Interpretations of static grain growth and linking grain size to stress are debated.