Comparison of Color Change Gem
Transmission and Absorption Spectrums.
Transmittance spectra for UE tourmaline, color shift garnet and chlorophyll.
Figure courtesy of Asbjørn Halvorsen

Transmission spectra for Usambara effect tourmalines (red), chlorophyll solution (green) and color shift garnets (purple). The garnet spectrum is based on Manson and Stockton, 1984 figure 4).
Absorption spectra for chromium bearing minerals.
Figure courtesy of Asbjørn Halvorsen

Chromium bearing minerals classified as three spectral groups according to Neuhaus (1960), with location of absorption maxima I and II for the three groups.

See also: Usambara Effect transmission curves.
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Usambara Effect