Staurolite Spectra (1000 - 5000 nm)
Staurolite, (Fe2+)2Al9Si4O23(OH), 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.
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