The present work deals with thermal and XRD analysis of fluoro-topaz synthesis by sintering of aluminium and silicon oxides (in the form of corundum and quartz) with ammonium fluoride and carried out in open Pt crucibles (for XRD studies) and a closed furnace of simultaneous DTA/TG thermoanalytical apparatus called MOM Derivatograph. The furnaces are connected to a gas suction device to remove gas decomposition products. The study shows the endothermic peak at 125-155 degrees C, representing the formation of ammonium aluminium hexafluoride and cryptohalite. The endothermic peak at 220-240 degrees C represents the beginning of dissociation of ammonium aluminium hexafluoride to the more stable ammonium aluminium tetrafluoride. The endothermic peak at 340-350 degrees C represents the dissociation of cryptohalite and ammonium aluminium tetrafluoride with the formation of aluminium fluoride. The formation of fluoro-topaz is represented by the wide endothermic peak at 770-800 degrees C. The medium wide or sharp endothermic peaks at 950 degrees C and 1000 degrees C represent the subsequent dissociation of fluorotopaz to corundum or mullite, respectively. (c) 2012 Elsevier B.V. All rights reserved.