shows UV–vis absorption spectra of amethyst sample from Santa Maria (Rio Grande do Sul—Brazil). We observed the presence of a broad absorption band at about 540 nm in the spectrum of the gamma-irradiated sample (Fig. 2AI). In addition,one notices the presence of an intense absorption in the near UV region, with extensions into the visible region. The combination of
these bands gives rise to a deep purple colored material. Upon heat-treating this sample the broad band at 540 nm was no longer apparent, leading to a light yellow colored sample (Fig. 2AII).The gamma-irradiated prasiolite sample from Uberlândia (Minas Gerais—Brazil) showed a deep green color. Its UV–vis spectrum exhibited a broad absorption band in the visible region