Influence of structural relaxation on the low-temperature thermal conductivity of ancient natural glasses

The thermal conductivities of two natural glasses, amber and obsidian, were measured over the temperature range 0.06–10 K both in the as-received condition and following heat-treatments near and above the glass-transition temperature. The of amber decreased 6% with heat treatment revealing that this glass had undergone configurational relaxation during the 10⁷ years prior to measurement, but with a relaxation time greater than seven years. The of the obsidian did not change with heat treatment, a null result possibly produced by the ratio of oxides comprising the glass.