Structure Refinement and Thermal Stability of Creedite

摘要

The crystal structure of the mineral creedite (hydrous calcium aluminum sulfate fluoride, Ca3Al_2(F,OH)_10(SO_4).2H_(2O)) has been determined by Rietveld powder diffraction analysis. X-ray diffraction data obtained in the temperature range from 25 to 470℃ indicate that the crystal structure of creedite is stable up to 390℃. We have measured the unit-cell parameters of creedite as functions of temperature and determined its thermal expansion coefficients. Above 390℃, the mineral decomposes.