Enthalpy of diaplectic labradorite glass |
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Authors: | K L Geisinger A Navrotsky J Arndt |
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Institution: | 1. 10017 Spring Lake Terrace, 12030, Fairfax, VA, USA 2. Dept of Geological and Geophysical Sciences, Princeton University, 08544, Princeton, NJ, USA 3. Mineralogisch-Petrographisches Institut, Universitat Tübingen, 7400, Tübingen, Federal Republic of Germany
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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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