There is growing interest in the mid-infrared spectral region (8-14 mu
m) as both a laboratory and a remote sensing tool in geology, because
this portion of the spectrum contains the characteristic, fundamental,
molecular vibration bands for silicates and other mineral groups. How
ever, it is necessary to understand the relationship between the spect
ra of mineral mixtures and those of individual minerals in the mixture
in order to completely interpret and predict mineral abundances from
infrared data. Results of this study show quantitatively for the first
time that the spectra Of particulate mixtures of silicate minerals in
this wavelength region combine linearly by volume within a very small
error, as long as particles are much larger than the wavelength so th
at volume scattering is insignificant compared to surface scattering.
Results here apply specifically to mineral samples in the 75-250 mum s
ize range. They imply that we can predict the spectral response of a r
ock if the constituent minerals and their abundances are known. More i
mportantly, our results indicate that the relative quantities of miner
als in simple mixtures can be predicted to within 12% in the worst cas
e, and more typically to within 5%. Consequently, geologists should be
able to unmix the composite spectra Of rocks to determine mineral abu
ndances. This is important for both laboratory rock identification and
remote sensing applications. By better understanding how component mi
neral spectra mix in the spectrum of a rock, we can also better choose
spectral band positions and resolutions in infrared remote sensing fo
r compositional identification.