Thermal expansion of andalusite and sillimanite at ambient pressure: a powder X-ray diffraction study up to 1000℃

摘要

The unit-cell parameters of andalusite and sillimanite have been measured by high-T powderX-r ay diffraction up to 1000oC at ambient pressure. Within the temperature range investigated, all the unitcell parameters varied smoothly, indicating no phase transition. The volume-temperature data were fitted with a polynomial expression for the thermal expansion coefficient (α_T = a_0+ a_1T + a_2T~(-2)), yielding a_0 = 2.55(2)610~(-5)K~(-1), a_1 = 0 and a_2 = 0 forandalusite, and a_0 = 1.40(4)610~(-5)K~(-1), a_1 = 7.1(8) ×10~(-9)K~(-2) and a_2 = 0 for sillimanite. Using the new thermal expansion data determined in the present study and compressional data from the literature, the P-T phase relations of the kyaniteandalusite-sillimanite system were calculated thermodynamically, with the invariant point located at ～523℃ and 3.93 kbar.