Absorption spectrum of dark purple fluorite, Kent deposit, Kazakhstan

[Display omitted] •Uranium irradiation leads to dissociation of CaF2 with the formation of F2 molecules in the matrix of a natural crystal.•Absorption bands in the UV part of the spectrum are associated with the formation of Ca metallic colloids centers.•Heat treatment leads to discoloration of the crystals due to the reverse flow of the dissociation reaction. The absorption spectrum of splinted samples of dark purple fluorite of Kent deposit, Kazakhstan and its evolution at the heating of mineral samples was studied. Along with a strong band related to calcium colloids there are spectral bands connected with yttrium impurity and a band hypothetically caused by uranium. Concentration of calcium within colloids in the samples was determined. The mineral heating results in the disappearance of colloid absorption and decrease of structureless background that is connected with light scattering by colloids, fluorine bubbles and lattice defects. The striped nature of the samples studied is probably due to nonlinear crystallization dynamics of a CaF2–UF3 solid solution. The pattern arising due to this process depends on both uranium concentration and the crystallization conditions in the process of mineral growth.