An exceptional gem-quality imperial topaz crystal, reddish-orange in color, weighing 286.6 grams, has been in the collection of the Museum of Mineralogy for over 150 years. The sample comes from the Ouro Preto area (Minas Gerais, Brazil); this area is currently the only one in the world from which imperial topaz of a color and clarity such as to make it usable also in the gemological field is extracted. The term "imperial" associated with topaz is used exclusively for crystals that have varying colors from yellow-orange, to orange-pink, to orange-reddish, to red, to purple; nowadays it has become almost impossible to extract samples of exceptional quality and large dimensions; in the very rare cases in which this occurs, imperial topaz crystals reach astronomical market prices and are almost always cut to be used in high jewelery. These factors contribute to making the imperial topaz of the Museum of Mineralogy of Sapienza even more extraordinary: this crystal, which has remained intact for decades and preserved from the cut, came into the collection at a time when the best pieces still reached important institutions. museum - unlike today, where the best samples are the prerogative of wealthy private collectors -, according to many experts, represents the best example of imperial topaz in the world.