Staurolite spectra

Staurolite Spectra (1000 - 5000 nm)

Staurolite is an example of a mineral containing Fe²⁺ in a site of four-coordination. Consequently, the absorption from iron is in the near-infrared portion of the spectrum as is shown in the spectrum below. The color of staurolite is due primarily to the Fe²⁺ - Ti⁴⁺ intervalence charge transfer transition. Occasionally, other metal ions, such as cobalt, can enter straurolite and cause color.

Image of a representative staurolite spectrum

Spectrum of a staurolite from Pizzo Forno, Switzerland. Plotted for 0.098 mm thickness. Same plot on a wavenumber (Energy) scale where 10,000 cm^-1 = 1000 nm. Just the 300-1500 nm region. The orange -brown color is mostly from the iron-titanium intervalence charge transfer. The sharp features near 3500 cm^-1 are due to OH^- ions. The bands in the near-infrared are from Fe²⁺ in the tetrahedral site. Data Files: E\\a=beta; E\\b=alpha; E\\c=gamma
Spectrum of blue cobalt-containing staurolite from a diasore-bearing metabauxite lens on the eastern coast of Samos Island, Greece, near Mikri Lakka. Plotted normalized to 1.0 mm thickness. The color comes from Co²⁺ in the tetrahedral site. Just the 300-1000 nm region. Contributed data from Michail N. Taran, Kiev, to appear in American Mineralogist. Data Files: alpha, beta, gamma

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