Heat transport properties of cristobalite and discussion of "snowflake" formation

Thermal diffusivity (D) was obtained from cristobalite formed via melting slightly hydrous fused silica using laser flash analysis. Natural samples have lower D due to contamination (e.g., with feldspar) or to varying amounts of pore space. Data collected from cristobalite from 298 to 1300 K is fit by 14.11×10⁶T ^-2.+0.000493T mm²/s. Values of D (e.g., 1.85 mm²/s at 298 K) and thermal conductivity are similar to those for rhyolite and silica glass, but higher than their melt values, consistent with cristobalite being highly disordered, but without the additional degree of freedom for a melt. Formation of snowflake obsidian is discussed in view of our synthesis experiments.