Influence of mineral (prefered) orientation on composition mapping: Observed in IR range of transmission spectra

Spectra of powdered mineral samples are used for calibration of air-borne data and for quantitative estimation of mineral content. However, in natural environments, minerals can be orientated in a specific manner and their lattices are usually unbroken. Using powders, we minimize orientation effects, but thereby creating a level of uncertainty that should be evaluated. In this study, we attempt primarily to estimate the mineral lattice orientation effect and its expression in spectral signature. The simple case of hornblende-amphiboles (in amphibolites) was observed. An un-mounted thin section, free from epoxy, was prepared, and its transmittance was measured with an FTIR (Fourier Transform Infra-Red) micro-spectrometer in 1-2.5 mum. spectral range. Results show spectral variance caused by mineral (preferred) orientation: changing depth of absorptions, spectral shape and transmittance levels.