Figure 6. Ionic radii of trivalent ions such as Mn, Fe, and Cr (isovalent to Al3+, in solid circles) closely match those of Al3+ and can readily replace Al3+ as chromophore ions.For a 5 mm thickness, UV-visible spectra were calculated for various chromophore concentrations based on experimentally collected hiddenite and kunzite absorption spectra. Figure 7 compares the effectiveness of Cr and Mn as chromophores.