Thermal expansion coefficients for indialite,emerald, and beryl

Thermal expansion coefficients ?₁ and ?₃ calculated for the hexagonal minerals indialite, emerald and beryl are, in general, small with ?₃ being negative near room temperature. This unusual behavior leads to low volume coefficients of thermal expansion (β=2?₁+?₃) making these materials ideal ceramic bodies for catalyst carriers in air-pollution control. The temperature at which the c-cell edge length of beryl is a minimum is strongly dependent upon the presence of trace amounts of impurity atoms. This effect is ascribed to changes in the Grüneisen parameters.