Structural and crystal-chemical response of glauconite globules to pH under static aqueous conditions

Abstract

Glauconite-bearing sediments and glauconite-based mineral materials may interact with waters of contrasting pH, but the response of intact glauconite globules under static water-mineral conditions remains poorly constrained. The present study evaluated whether pH-driven interaction modifies the layered structure, crystal chemistry, and near-surface texture of natural glauconite globules while preserving their natural granular morphology. Natural glauconite was reacted with distilled water-based solutions at pH 2, 3, 4, 6, 7, 8, 9, and 10 for 1, 3, 7, 14, 30, and 60 days under static conditions. The mineral fractions were examined by X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, and Fourier-transform infrared spectroscopy. The results show that the 10 Å layered TOT structure of glauconite was preserved in all experimental series. Under acidic conditions (pH 2–4), a slight, steady decrease in d ₀₀₁ was observed. This decrease was accompanied by peak broadening and reduced intensity of basal reflections, signifying increased structural disorder without structural destruction. The diagnostic (060) reflection was preserved in all samples ( d ₀₆₀  = 1.508–1.514 Å), confirming the stability of the dioctahedral octahedral framework. Crystal-chemical data showed a distinct pH- and time-dependent adaptive response in the interlayer and tetrahedral domains. In acidic solutions, interlayer K decreased by ~25–45% relative to the initial composition, with maximum deviations noted after 14 days of interaction. These changes were accompanied by an increase in Al in the tetrahedral sheet (up to +0.05–0.32 a.p.f.u.) relative to the initial state. In contrast, structural and crystal-chemical changes were minimal under neutral plus alkaline conditions. Morphological changes of glauconite globules were mainly confined to near-surface zones. Overall, the results indicate that glauconite globules show high structural stability in static aqueous environments, with only limited pH-dependent structural, chemical, and near-surface modifications.