EXSOLUTION AND AL-SI DISORDER IN ALKALI FELDSPARS - THEIR ANALYSIS BYINFRARED-SPECTROSCOPY

An experimental method for the determination of Ab-Or exsolution and A l-Si ordering in alkali feldspar is described. Powder infrared spectro scopy was used to measure spectra in the spectral range between 50 and 1500 cm(-1) using about 5 mg of sample material. The spectra were ana lyzed using reference spectra of uniform samples with various Ab-Or co mpositions and several degrees of Al-Si order. The application of this method is demonstrated for two examples of exsolved feldspar minerals , and it is shown that detailed characterization of alkali feldspars u sing IR spectroscopy leads to new insight into their structual details .