Mineralogical and spectroscopic characteristics of prasiolite-bearing amygdales from Sokołowiec (Lower Silesia, Poland)

Prasiolite-bearing amygdales from Sokołowiec (Lower Silesia, Poland) were investigated using combined microscopic and spectroscopic techniques, supported by bulk chemical analysis, to constrain their origin and potential factors responsible for the development of a greenish hue. The amygdales are hosted by Permian basaltic rocks of the North-Sudetic Basin and bear a distinctive crystallization sequence involving banded length-fast chalcedony with minor quartzine, prasiolite, and colourless quartz. The prasiolite-rich areas are composed of both colloform-banded and elongated quartz that exhibits uniform dull reddish cathodoluminescence emission. The elongated (,,normal”) quartz in prasiolite is further intermixed with water- and/or moganite-enriched feathery regions (i.e. with splintery appearance under polarizing microscope) that indicate a pervasive recrystallization of poorly crystalline/amorphous silica, rather than simple open-space crystallization during low-temperature hydrothermal conditions. These feathery regions are further coloured white in the macroscale and decrease the intensity of the overall greenish hue. The recrystallization fronts and textural boundaries, marked by the presence of elongated quartz with flamboyant/filamentous fabrics, host abundant solid inclusions embracing Fe oxides (hematite), clay minerals, and rare Zr-rich compounds that invoke a potential influence of natural radiation on the formation of prasiolite’s colour centres. Both prasiolite and colourless quartz contain similar concentrations of such impurity elements as Fe, Ti, Mn, and Al, although the former is slightly enriched in Ca, whose potential role as a charge-compensating ion should be considered in future studies.