High Resolution FTIR Spectroscopic Characterization of Hydrous K-feldspar from the Swiss Alps

Abstract

Feldspar is the most common mineral in the Earth?s crust. Every natural feldspar contains measurable amounts of hydrogen serving as one of the largest reservoirs for water on Earth. Bound hydrogen is coupled with specific chemical impurities distinguishable through the characteristic stretching energy of the X-OH hydroxyl bond. The abundance and type of hydrous impurity, incorporated into the crystal lattice during crystal growth, provide valuable insights into the thermodynamic conditions of their host geologic environment. We collected several gemmy crystals of hydrothermal K-feldspar (adularia) from the Swiss Alps and present here the first high-resolution (100-?m spot size) FTIR spectroscopic measurements on feldspar. Earlier studies of water in K-feldspar focused on igneous host rocks and have not attempted to discern internal variations in the impurity abundance within single crystals. These studies have identified different absorption bands within K-feldspars from different igneous environments. We show that individual Swiss hydrothermal K-feldspars each show every major absorption band that has been observed in their igneous counterparts. In addition, internal variations in impurity abundances of single crystals show potential for discerning variations in the fluid conditions present during crystal growth and/or post-crystallization thermal history.