Transport properties of high albite crystals, near-endmember feldspar and pyroxene glasses, and their melts to high temperature

Thermal diffusivity (D) was measured using laser-flash analysis (LFA) from oriented single-crystal albite and glasses near LiAlSi₃ O₈, NaAlSi₃O₈, CaAl₂ Si₂O₈, LiAlSi₂O₆ and CaMgSi₂O₆ compositions. Viscosity measurements of the supercooled liquids, over 2.6× 10⁸ to 8.9× 10¹² Pa s, confirm strongly non-Arrhenian behavior for CaAl₂Si₂O₈, and CaMgSi₂ O₆, and near-Arrhenian behavior for the others. As T increases, D_glass decreases, approaching a constant near 1,000 K. Upon crossing the glass transition, D decreases rapidly. For feldspars, D for the melt is ∼15% below D of the bulk crystal, whereas for pyroxenes, this difference is ∼40%. Thermal conductivity (k_lat = pC_PD) of crystals decreases with increasing T, but k_lat of glasses increases with T because heat capacity (C_P) increases with T more strongly than density (p) and D decrease. For feldspars, k_lat for the melt is ∼10% below that of the bulk crystal or glass, whereas this decrease for pyroxene is ∼50%. Therefore, melting substantially impedes heat transport, providing positive thermal feedback that could promote further melting.