Euclase Visible Spectra (300 - 2000 nm)

Euclase, BeAlSiO₄(OH), is intrinsically colorless. All color is from minor components.

Euclase absorption spectrum

• GRR 557 spectrum; from the Miami Gneiss shield, in a deposit between Karoi and Miami, Zimbabwe. Plotted as 0.400 mm thick. The color of this material comes from Fe²⁺ - Fe³⁺ intervalence charge transfer that causes the band centered near 670 nm. This dark blue crystal has about 0.05 wt% Fe (reported as FeO). Data Files: E|| alpha; E|| beta=b; E|| gamma.

 
Euclase from Alto Jacu Equador, Rio Grande do Norte, Brazil

A portion of the structure of euclase showing the zig-zag chain of Al octahedra. Fe³⁺ and Fe²⁺ enter this chain to cause the blue color. Some crystals are light green, such as some from Brazil. Their color is from a minor amount of Cr³⁺.

In the monoclinic crystal system, two of the extinction directions along which the spectra are measured do not coincide with the a- and c-crystallographic axes. Thus, the a-axis has components of both the alpha and the gamma spectra.

Link to references to color and visible spectroscopy of euclase

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