Topaz is one of the few minerals whose color is due not to impurities, but to structural defects (so-called atomic vacancies). O vacancies give blue color, F vacancies give yellow color, O and SiO2 vacancies give smoky color. When heated, the color disappears; when exposed to radiation, it intensifies.
As a rule, most deep blue and blue topaz on the market have this color due to irradiation. At Minty Sky, we use only natural blue topaz, which is quite pale in appearance, but has a blue tint of natural origin.
Topaz is one of the reference minerals of the Moss hardness scale - the value of this indicator for topaz is 8, while, for example, for turquoise this indicator takes values of about 5, for minerals of the quartz group - 6-7. That is, topaz is much harder than most semi-precious stones.