Electrolytic coloration and spectral properties of natural calcite crystals

Natural colorless calcite crystals are colored electrolytically by using a pointed cathode and a flat anode at various temperatures and voltages. Ca + and CO 3 − color centers, Ca 2+ vacancies, and CO 3 2− units are produced in colored crystals. Absorption spectral bands of the Ca + and CO 3 − color centers, Ca 2+ vacancies, and CO 3 2− units are reported for the colored crystals at room temperature. Pb 2+ spectral bands are observed in absorption and fluorescence spectra of uncolored and colored crystals. The current-time curve for electrolytic coloration of natural calcite crystal and its interpretation with respect to the electrolytic coloration process are given. Creation and conversion of color centers are explained.