Alkali feldspars as a main phosphorus reservoirs in rare‐metal granites: three examples from the Bohemian Massif (Czech Republic)

Phosphorus‐rich alkali feldspars were found in three peraluminous highly differentiated albite‐topaz‐Li‐mica granites in the W and S parts of the Bohemian Massif. The average contents of P2O5 in K‐feldspars (Křížovy kámen 0.57 wt%, Homolka 0.77 wt%, and Podlesí 0.83 wt%) are higher than the average contents of P2O5 in albites (Křížovy kámen 0.23 wt%, Homolka 0.23 wt%, and Podlesí 0.39 wt%). The analyses of feldspars indicate that partition coefficient of phosphorus between K‐feldspar and albite range from 1.5 to 2.5. Measured data in K‐feldspars suggest a statistically significant difference from the Al3++P5+=2 Si4+ substitution mechanism for higher phosphorus concentration. The P‐content in K‐feldspars from the Podlesí‐granite represent the highest P‐content in natural feldspar known to date (up to 2.5 wt% of P2O5)‐ It is suggested that all studied granites retained nearly all phosphorus of granitic melts and that their alkali feldspars represent major reservoirs of phosphorus.