Sillimanite Visible Spectra (generally 350 - 1200 nm)

Images of representative sillimanite, Al₂SiO₅

Visible Spectra: polarizations: (a = alpha direction; b = beta direction; g = gamma direction) Fe³⁺ is usually responsible for the yellow color in sillimanite. Chromium 3+ can contribute to the spectrum. Other colors can occur when intervalence charge transfer is involved.

• GRR 273 spectrum; sillimanite, Reinbolt Hills, Antactrica, NMNH 247011. Plotted as 5.0 mm thick with a typical yellow color from Fe³⁺. Data Files: a 9K; g 5K
• GRR 380 spectrum; sillimanite, Benson Mines, NY, NMNH 115586.  Plotted as 0.40 mm thick.
• GRR 382 spectrum; sillimanite, Sardinia, plotted as 0.50 mm thick. Purple-brown color from Fe³⁺ and intervalance charge transfer presumed to be from Fe²⁺ and Ti⁴⁺. Data Files: a 3K ; b 1K ; g 6K
• GRR 383 spectrum; sillimanite, Gilford, CT - Harvard collection 85919. Plotted as 0.60 mm thick. A brown sillimanite.
• GRR 386 spectrum; sillimanite, Norwich, CT, Harvard collection 85918. Plotted as 0.50 mm thick. A brown sillimanite.
• GRR 444 spectrum; sillimanite, Ceylon, Brittish Museum 1945,39. Plotted as 10.0 mm thick. The blue color comes from intervalance charge transfer. Data Files: a 3K ; c 4K
• GRR 518 spectrum; sillimanite, Forfinger Point, Enderbyland, Antarctica, with chromium features in the spectrum. Ploted as 3.0 mm thick.

Link to references about the spectra of silimanite

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