The spinels are a diverse group of minerals with wide variation in their chemical composition. Among the more common spinel group minerals, the color is due to chromium and iron. Rarely, cobalt will be a cause of color.

Visible Spectra (generally 350 - 2500 nm)

Natural Spinels

• Red Cr-spinel, Sri Lanka. The color comes from Cr³⁺. data file
• Blue cobaltian spinel, Yakutia kimberlite pipe, Russia. Approximately 0.05 mm thick. The color comes from Co²⁺ in the tetrahedral site. Contributed data from Michail N. Taran, Kiev: data file. Picture of the crystal and the area of measurement.
• Blue cobaltian spinel, Samos Island, Greece. Plotted normalized to 10.0 mm thickness. The color comes from Co²⁺ in the tetrahedral site. Contributed data from Michail N. Taran, Kiev: data file. 
• Blue cobaltian spinel, Baffin Island, Nanavut, Canada. The blue color of the crystals comes from Co²⁺ in the tetrahedral site. 0.849 mm thick. data file
• Blue gahnite, locality unknown. The color is from Fe²⁺. data file
• RDS-153c Pink spinel from Tanzania containing both Cr³⁺ and Fe²⁺. Here we see the near-infrared region showing the absorption bands from Fe²⁺ in the tetrahedral site. 0.503 mm thick; 1.028% FeO. Sample Sp3 of Shannon & Rossman (1991) J Phys Chem Solids 52, 1055. data file

Synthetic Spinel-group materials

• MgAl₂O₄:Cr spinel, synthesized by the flux method in Novosibirsk, Russia.  Normalized to 10.0 cm.  Colored by Cr³⁺.  Data File: Contributed data from Anton Vasiliev, LAL, Moscow: Spinel_Red, 25 K.
• MgAl₂O₄:Co spinel, synthesized by the flux method in Novosibirsk, Russia.  Normalized to 10.0 cm.  Colored by Co²⁺.  Data File: Contributed data from Anton Vasiliev, LAL, Moscow: Spinel_blue, 25 K.
• Ni₂SiO₄ Spinel, published in Rossano et al. European Journal of Mineralogy 1996:8, 471-475. Data file: Contributed data from Stephanie Rossano, Paris:  data file, 15 K.

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