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