Tuhualite Visible Spectrum (300 - 2500 nm)

Image of the tuhualite absorption spectrum

• GRR 388 spectrum from Opo Bay, Mayor Island, North Island, New Zealand   Plotted as 0.050 mm thick. The crystal in this picture of a thin section (polarized E||b) is one of the original specimens collected by Hutton. The purple color of this material comes from Fe²⁺ - Fe³⁺ intervalence charge transfer. The structure determination indicates that the Fe²⁺ is in a highly distorted tetrahedral site (purple) and the Fe³⁺ is in an octahedral site (green). These sites form a zig-zag chain of alternating tetrahedra and octahedra that runs parallel to the c-axis. In polarized light, the color of the mineral varies considerably with the direction in which it is observed. Data Files: E|| alpha = a-axis; E|| beta = b-axis; E|| gamma = c-axis.

Contrary to the published formula, our work indicates that tuhualite is an anhydrous mineral.

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