In physics and chemistry, sublimation is the direct change from the gas state to the solid state, skipping the liquid state, and vice versa. Volcanic gases are made up of 95% water. The remaining 5% of the volume is dissolved sulphur, fluorine, chlorine and carbon dioxide.
When the temperature drops rapidly from over 100 °C to room temperature, 20-25 °C, the substances dissolved in the gas precipitate in the form of sulphur crystals
cristalletti di zolfo