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

• Almandine ---------- Fe²⁺₃Al₂(SiO₄)₃
• Andradite ----------- Ca₃Fe³⁺₂(SiO₄)₃
• Grossular ----------- Ca₃Al₂(SiO₄)₃
• Pyrope -------------- Mg₃Al₂(SiO₄)₃
• Spessartite ---------- Mn₃Al₂(SiO₄)₃
• Uvarovite ----------- Ca₃Cr₂(SiO₄)₃

Other, less common end-member compositions are:

• Calderite ------------ Mn₃Fe³⁺₂(SiO₄)₃
• Goldmanite --------- Ca₃V₂(SiO₄)₃
• Hibschite ------------ Ca₃Al₂(SiO₄)_3-x(OH)_4x 0.2 < x < 1.5
• Katoite -------------- Ca₃Al₂(SiO₄)_3-x(OH)_4x x > 1.5
• Kimzeyite ----------- Ca₃(Zr,Ti)₂((Si,Al,Fe³⁺)O₄)₃
• Knorringite ---------- Mg₃Cr₂(SiO₄)₃
• Majorite ------------- Mg₃(Fe,Al,Si)₂(SiO₄)₃
• Morimotoite -------- Ca₃Ti⁴⁺Fe²⁺(SiO₄)₃
• Schorlomite --------- Ca₃Ti⁴⁺₂((Fe³⁺₂Si)O₄)₃

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

• Picture of a colorless grossular from Asbestos, Canada               

Dark red to pink garnets with Fe²⁺

Almandine, GRR 1056, Umba River Valley, Tanzania, colored red by Fe²⁺; data file

Pyrope, GRR 131, unknown locality, probably Tanzania, colored pink by Fe²⁺;. data file

Vis-NIR region: 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

Orange garnets with Mn²⁺

• Spessartine, GRR 72, Rutherford Mine, VA, colored orange by Mn²⁺ 3.45 mm thick; data file
• Spessartine, GRR 43, Rutherford Mine, Amelia, VA, colored orange by Mn²⁺, expanded view from a 2.165 mm thick sample. data file
• Pyrope-spessartine, GRR 1267, Kenya, 1.686 mm thick; data file

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

• Andradite, GRR 568, variety melanite (black when thick), San Benito Mountains, California, with both Fe³⁺ and Ti⁴⁺, 0.102 mm thick. data file
• Andradite (variety melanite), GRR 755, Santa Rita Peak, San Benito Mountains, California. This garnet is black, but when thinned, becomes dark brown-orange. The sharp peak near 441 nm is from Fe³⁺; 0.045 mm thick, data file
• Grossular, GRR 1113, (orange-brown), North Hill, Riverside, California. (Ca_2.86 Fe_0.12 Mn_0.02)  [Al1.52 Fe0.43 Ti0.05], with both Fe²⁺ and Fe³⁺, 0.336 mm thick. data file
• Grossular GRR 1386, (brown), Lalatema, Moshi, Kenya, 4.126 mm thick. Data file

Yellow-green garnets with Fe³⁺

• Andradite, GRR 48, Val Malenco, Sondrio Province, Italy, colored greenish-yellow by Fe³⁺, 1.03 mm thick;  data file
• Grossular GRR1934b from Sierra de las Cruces, near Lake Jaco, Chihuahua, Mexico, 2.60 mm thick. This is a yellow-green rim on a crystal with a small black core.  Data file

Green garnets with V³⁺ and Cr³⁺

• Uvarovite, GRR 1019, Jacksonville, California, colored green by Cr³⁺, 0.029 mm thick. data file
• Grossular, variety Tsavorite, GRR 229, Tanzania, colored green by V³⁺, 0.758 mm thick. data file
•  Andradite, variety demantoid, GIA 2952, Russia, 2.5 mm thick. The bright green garnet has both the features of Fe³⁺ and the features of Cr³⁺. Data file

Red garnets with Cr³⁺

• Red pyrope, GRR 1055, Moses Rock, Utah, Chromian-pyrope, Ca0.33 Mn0.02 Mg2.13 Fe0.54 Al1.95 Cr0.07, 0.840 mm thick; data file

Red and pink garnets with Mn³⁺

• Raspberry-red grossular GRR1890 from Sierra de Cruces Range, Coahuila, Mexico, 1.17 mm thick.  Data File.

Blue to purple garnets

• Pyrope, GRR 2224, Tunduru, Tanzania. This is a color-change garnet that goes from pale purplish-blue to light purple depending upon the illumination, 2.426 mm. Data file.

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