Abstract
Enthalpies of solution in molten 2PbO·B2O3 at ∼988 K have been measured for diaplectic labradorite glass from the Manicouagan impact crater and a fused glass formed from the same material. The enthalpies of solution of the diaplectic and fusion-formed glasses are 4,347 and 2,023 cal mol−1, respectively. The more endothermic enthalpy of solution of the diaplectic glass indicates a greater relative energetic stability of about 2.3 kcal mol−1. The data are consistent with Diemann and Arndt's (1984) structural model that suggests the diaplectic glass is more ordered than fusion-formed glass and with the presence of crystallites. Comparison of data to enthalpies of solution of crystalline labradorite (Carpenter et al. 1985) indicates a maximum percentage of crystalline relics of ∼15–18%, also consistent with Diemann and Arndt's (1984) estimate of <17%. Thus the diaplectic glass is intermediate in thermochemical properties between normal glass and crystal (much closer to glass) and does not represent any state more unstable than normal fusion-formed glass.
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Geisinger, K.L., Navrotsky, A. & Arndt, J. Enthalpy of diaplectic labradorite glass. Phys Chem Minerals 13, 357–359 (1986). https://doi.org/10.1007/BF00309180
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DOI: https://doi.org/10.1007/BF00309180