The paper presents data on a new fumarolic mineral (aqueous Al-Ca chloride-sulfate) discovered on Tolbachik Volcano eruption in 1975-1976. The mineral has no analogs among natural and synthetic compounds. It was examined by X-ray diffraction analysis of mono- and polycrystals and X-ray microprobe analysis complemented by Cl and F determination by conventional chemical analysis and refined simultaneously with the decoding its atomic structure. Vlodavetsite is a precursor of ralstonite, fluorite, gypsum, and anhydrite, widespread minerals in a wall-rock alteration zone within the vent facies of the great Tolbachick fissure eruption.