The garnets constitute a group of minerals which share a common structure. Common end member compositions are:

Visible Spectra (generally 350 - 1100 nm)

As would be expected from a chemically complex group of minerals, garnets owe their color to a variety of causes. Absorption by Cr3+, V3+, Fe3+ (6-coordinated site), Fe2+ (8-coordinated site), Mn2+, and Fe2+ - Ti4+ intervalence charge transfer can all be found in the spectra of garnets.

Spectra of representative garnets

Colorless garnets

    When devoid of transition metals such as Mn, Fe, Cr, and V, grossular and pyrope garnets are colorless.

Dark red to pink garnets with Fe2+

  • Almandine GRR 1040, North River Garnet Company, Warren Co., NY, [Fe1.35 Mg1.30 Ca0.26 Mn0.03] Al1.98(SiO4)3; 1.54 mm thick; data file
  • Almandine, GRR 1056, Wrangell, Alaska, [Fe2.03Mg0.67Ca0.18Mn0.07]Al2.0(SiO4)3, colored light reddish-purple by Fe2+ 1056, normalized to 1.0 mm thickness; data file
  • Almandine, GRR 1776, dark reddish-purple gemstone, [Fe2.5Mg0.3Mn0.2Ca0.1]Al2.0(SiO4)3, probably from India, Graphed at 1.0 mm, normalized from 0.213 mm thickness. Visible region only; data file
  • Pyrope, GRR 83, rhodolite variety, Umba River Valley, Tanzania, colored pink by Fe2+; 0.78 mm thick;  data file
  • Pyrope, GRR 131, unknown locality, probably Tanzania, colored pink by Fe2+ pyrope 131; Approximate 8-coordinated site composition: Mg1.82 Fe0.99 Ca0.04 Mn0.04. Plotted as 2.007 mm thick; data file
  • Pyrope, GRR 1121i, Wesselton, South Africa, Mg2.32 Mn0.01 Fe0.43 Ca0.27 Al1.95 Cr0.02, 1.693 mm thick; data file
  • Pyrope, GRR 1121f, Wesselton kimberlite diamond mine, South Africa. Mg2.09 Mn0.02 Fe0.67 Ca0.26 Al1.89 Cr0.03 Ti0.03. Plotted as 0.547 mm thick; data file; data file
  • Pyrope-spessartine, GRR 1267, Kenya, sold commercially as "Malaya Garnets". 1.686 mm thick; data file
  • Pyrope, Mon-9, Monastery Mine, South Africa, 1.37 mm thick; data file . Showing the three near-IR Fe2+ bands and weaker broad OH bands that are visible in the 2800 nm region.
  • Orange garnets with Mn2+

    Orange to black garnets with Fe2+, Fe3+ and Ti4+

    Yellow-green garnets with Fe3+

    Green garnets with V3+ and Cr3+

    Red garnets with Cr3+

    Red and pink garnets with Mn3+

    Blue to purple garnets

    Luminescence Spectra of Garnets

    Link to an extensive collection of references to mostly color and visible spectroscopy of garnets

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    revised 25-Feb-2024