NIR reflectance spectroscopy of pyroxenes: ferroaugites, salites, hedenbergites

Pyroxenes are among the most ubiquitous minerals present on the surfaces of the terrestrial planets, most asteroids and meteorites. Because IR spectroscopic remote sensing is one of the most used techniques to investigate the compositional properties of planetary surfaces, it is important that the spectral properties of the main mineral phases be well understood. The NIR spectra of the pyroxenes are mainly characterized by the 1µm- and 2µm signatures. Their wavelength positions depend strongly on the chemical composition of these phases and is, on the whole, well known in the case of the ortho- and clinopyroxenes which are the most significant ones in planetary volcanics. However, moving to ferroaugitic, salitic, and hedenbergitic compositions the character of the spectra changes drastically. Thus the 1µm signatures become more and more complex and the 2µm signatures diminish or disappear completely. It appears that there are "ferroaugitic", "salitic", "hedenbergitic" spectra which are different from eaxh other. The reason for theses spectroscopic differences might be caused, above all, by variable oxidation states of these pyroxenes and, therefore, by variable portions of ferrous and ferric iron