Structural Mechanisms of Anomalous Thermal Expansion of Cordierite‐Beryl and Other Framework Silicates

The structural mechanisms controlling the anomalous thermal expansion behavior of the cordierite‐beryl type structure and other framework silicates are discussed. The expansion of a particular silicate framework depends on the temperature response of the framework itself involving T–O–T and O–T–O angular changes, the expansion coefficient(s) of the nontetrahedral bonds, if present, and the interplay between these two factors. For cordierite, beryl, and β ‐eucryptite, expanding nontetrahedral bonds play a critical role in driving the anomalous thermal expansion observed. For β ‐spodumene and the feldspars, the thermal response of the framework dominates the expansion mechanism. The effects of channel constituents on the thermal expansion of the cordierite‐beryl framework are also discussed.