Optical investigation revealed a great number of fluid inclusions in the imperial variety of topaz that occurs at several localities around Ouro Preto, Minas Gérais, Brazil. The inclusions are biphasic at 25 ºC and display several patterns of morphology, orientation, and dimensions. Microthermometric studies revealed that the inclusions are filled mainly with aqueous solutions and CO2 . Moreover, for all the morphological types of inclusion, temperatures of formation are always similar. The data also suggest that all the inclusions developed simultaneously or under very similar conditions of PT. On the other hand, distinct group of inclusions display peculiar characteristics suggesting some sort of interaction between the fluids and the country rock. Finally, one should bear in mind the influence of postcrystallization events on the composition and thermodynamic properties of the original fluid inclusions.
