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 LiAlSi3O8, NaAlSi3O8, CaAl2Si2O8, LiAlSi2O6 and CaMgSi2O6 compositions. Viscosity measurements of the supercooled liquids, over 2.6 x 10(8) to 8.9 x 10(12) Pa s, confirm strongly non-Arrhenian behavior for CaAl2Si2O8, and CaMgSi2O6, 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 similar to 15% below D of the bulk crystal, whereas for pyroxenes, this difference is similar to 40%. Thermal conductivity (k (lat) = rho C (P) D) 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 (rho) and D decrease. For feldspars, k (lat) for the melt is similar to 10% below that of the bulk crystal or glass, whereas this decrease for pyroxene is similar to 50%. Therefore, melting substantially impedes heat transport, providing positive thermal feedback that could promote further melting.