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

Other, less common end-member compositions are:

Also used is a name for intermediate hydrogrossulars:

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.

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 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 131, unknown locality, probably Tanzania, colored pink by Fe2+; data file
  • Pyrope, GRR 83, rhodolite variety, Umba River Valley, Tanzania, colored pink by Fe2+; 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, South Africa, 0.547 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

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    updated 17-Sep-14