The linear thermal expansion coefficients of a bronzite specimen with the approximate molecular formula (Mg.8Fe.2)SiO3 have been measured by an X‐ray diffractometer technique in the range 25°–1000°C in an air atmosphere. The linear thermal expansion coefficients determined for the crystallographic a, b, and c directions are α11 =. 0.164 × 10−4 °C−1, α22 = 0.145 × 10−4 °C−1, and α33 = 0.168 × 10−4 °C−1, respectively. No phase changes were observed in the temperature range studied.