END-MEMBER FELDSPAR CONCENTRATIONS DETERMINED BY FTIR SPECTRAL-ANALYSIS

Feldspar mineralogy, reported as concentrations of KAlSi3O8, NaAlSi3O8 , and CaAl2Si2O8, can be determined from FTIR spectroscopy. In this st udy end-member FTIR spectra were constructed from sample spectra and t heir associated K-, Na- and Ca- feldspar concentrations using a least- squares full spectrum program. This was necessary because none of the samples have single-phase, pure end-member composition. The K-, Na-, a nd Ca-feldspar concentrations are computed by fitting the sample FTIR spectrum to the end-member FTIR spectra using a nonnegative least-squa res program. For the feldspar samples examined we found that when the compositions determined from infrared spectroscopy are compared to the compositions derived from chemistry, the standard error of estimate f or K-, Na-, and Ca-feldspar is 1.0, 0.9, and 0.7 absolute mole %, resp ectively.