Ratovkite

Finely-dispersed fluorite of sedimentary origin and with deep-violet colour due to irradiation. First described from the Moscow area in the early 19th century.
This variety has not a true sedimentary origin but only forms within marine sedimentary rocks from cold ground waters. During oxidation of pyrite in overlying black Jurassic clays, a lot of sulphuric acid forms. This acid reacts with fluorcarbonate-apatite fossils (phosphorites) with formation of free HF. These cold diluted downward solutions of H2SO4 + HF penetrate into underlying dolomitised limestones of Carboniferous age and dissolve carbonates, with subsequent formation of fluorite as veinlet fillings, precipitates and impregnations within massive limestones.
Due to elevated contents of uranium and subsidiary radionuclides in the black Jurassic clays, these groundwater solutions are enriched by radon, the decay of which produces gamma-rays. The latter impart a deep violet radiation colouration to the newly formed fluorite precipitates.
This is the characteristic feature separating ratovkite from other sedimentary fluorites.