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Abstract:

The blue quartz of the Albești metagranite is an interesting and puzzling occurrence in the Romanian geological landscape, both in terms of rarity and available data. The body of literature on blue quartz attributes the color to the Rayleigh/Tyndall scattering of light by nanometer/submicron inclusions, commonly identified as ilmenite or rutile, and as a theoretical possibility, fluid inclusions. The Albești blue quartz undergoes a visible loss of color at temperatures as low as 300°C, and for this reason the most commonly cited light scattering inclusions cannot be the cause of the coloration. Furthermore, there are only a handful of occurrences known to exhibit such a thermal behavior, potentially placing the Romanian occurrence in a rather exclusive class of rock forming blue quartz. The data gathered by optical observations, heat treatment, powder diffraction, infrared spectroscopy, and scanning electron microscopy have shown that the blue color is produced by light scattering, the scattering particles are sensitive to heat, recrystallization can also affect the color, and that the color is likely metamorphic in origin. Despite the fact that the identity of the scattering particles is still unknown (although fluid inclusions, and molecular colloids are suggested as potential light scattering elements), there is strong indication that the color is metamorphic in origin and that it could be used as a marker for a specific set of metamorphic conditions. The results of the present study constitute a first significant step in the understanding of the Albești blue quartz and point in the direction of future research.