Glass stability (GS) of chemically complex (natural) sub-alkaline glasses

Glass stability (GS) indicates the glass reluctance or ability to crystallise upon heating; it can be characterised by several methods and parameters and is frequently used to retrieve glass-forming ability (GFA) of corresponding liquids as the case with which such liquids can be made crystal free via melt-quenching. Here, GS has been determined for the first time on six sub-alkaline glasses having complex (natural) compositions, the most widespread and abundant on Earth. KT, KH, KW, KLL and w2 GS parameters increase linearly and monotonically as a function of SiO2, with very high correlations. Moreover, Tx values and GS parameters highly correlate with GFA via Rc (critical cooling rate), previously determined with ex-situ cooling-induced experiments. Therefore, GS scales with GFA for natural silicate compositions. In addition, the in-situ Rc value of B100 measured with DSC results > 45 {\deg}C/min (> 2700 {\deg}C/h), broadly corroborating the Rc of about 150 {\deg}C/min (9000 {\deg}C/h) determined ex-situ. In turn, relevant solidification parameters on heating or cooling can be obtained by DSC investigations also for chemically complex (natural) systems, similar to simple silicate systems. These outcomes are relevant for lavas or magmas that re-heat glass-bearing volcanic rocks, as well as for fabricate glass-ceramic materials with desirable texture and composition of phases starting from abundant and very cheap raw volcanic rocks.

💡 Research Summary

The authors present the first systematic investigation of glass stability (GS) for six naturally occurring sub‑alkaline silicate glasses that represent the most abundant volcanic compositions on Earth. Using differential scanning calorimetry (DSC) they measured the glass transition temperature (Tg), the onset of crystallization (Tx) and the melting temperature (Tm) for each composition. From these fundamental temperatures they calculated five widely used GS parameters—KT = (Tx‑Tg)/(Tm‑Tx), KH = Tx‑Tg, KW = Tx/Tg, KLL = Tx/(Tg+Tm)—and the crystallization width w₂ = Tm‑Tx.

A key result is the remarkably linear increase of all GS parameters with silica content (SiO₂). Correlation coefficients exceed 0.95, indicating that higher SiO₂ strengthens the polymerized network, raises Tx and consequently improves resistance to crystallization. This behavior mirrors the established notion that silicate glasses become more “stable” as the degree of polymerization grows.

The study then links GS to glass‑forming ability (GFA) by comparing the derived parameters with previously reported critical cooling rates (Rc) obtained from ex‑situ cooling experiments on the same glasses. Regression analyses reveal strong linear relationships between each GS metric and Rc (R² ≈ 0.9), with KH showing the highest correlation (R² ≈ 0.94). Thus, GS, which is measured on heating, can serve as a reliable proxy for GFA, traditionally assessed by cooling‑rate experiments.

A particularly insightful experiment involved the pure silica glass B100. By analyzing the DSC heating curve in real time, the authors estimated an in‑situ Rc exceeding 45 °C min⁻¹ (≈ 2700 °C h⁻¹). Although this value is lower than the ex‑situ Rc of about 150 °C min⁻¹ (≈ 9000 °C h⁻¹) reported earlier, both are of the same order of magnitude, confirming that DSC can provide meaningful Rc estimates even for rapid heating conditions.

The implications are twofold. First, the findings help predict how volcanic glasses will behave when reheated during magmatic processes, offering a quantitative tool to assess the likelihood of devitrification and its impact on magma rheology and eruption dynamics. Second, the ability to infer GFA from simple DSC measurements opens a low‑cost pathway for designing glass‑ceramic materials from abundant volcanic rocks. By selecting compositions with high GS (and thus low Rc), manufacturers can tailor heat‑treatment schedules to obtain desired crystalline textures while minimizing energy consumption.

In summary, this work demonstrates that glass stability, quantified through standard DSC‑derived parameters, scales directly with glass‑forming ability for complex natural silicate systems. The linear dependence on SiO₂ provides a straightforward compositional predictor, and the strong correlation with critical cooling rates validates GS as a practical, rapid screening tool for both geoscientific investigations of magmatic reheating and industrial development of inexpensive, compositionally diverse glass‑ceramics.