ALBERT

Description: Spectral measurements of sunlight reflected from planetary surfaces, when correlated with experimental visible-near-infrared spectra of rock-forming minerals, are being used to detect transition metal cations, to identify constituent minerals, and to determine modal mineralogies of regoliths on terrestrial planets. Such remote-sensed reflectance spectra measured through earth-based telescopes may have absorption bands in the one micron and two micron wavelength regions which originate from crystal field transitions within Fe2+ ions. Pyroxenes with Fe2+ in M2 positions dominate the spectra, and the resulting 1 μm versus 2 µm spectral determinative curve is used to identify compositions and structure-types of pyroxenes on surfaces of the Moon, Mercury, and asteroids, after correcting for experimentally-determined temperature-shifts of peak positions. Olivines and Fe2+-bearing plagioclase feldspars also give diagnostic peaks in the 1 µm region, while tetrahedral Fe2+ in glasses absorb in the 2 µm region as well. Opaque ilmenite, spinel and metallic iron phases mask all of these Fe2+ spectral features. Laboratory studies of mixed-mineral assemblages enable coexisting Fe2+ phases to be identified in remote-sensed reflectance spectra of regoliths. Thus, noritic rocks in the lunar highlands, troctolites in central peaks of impact craters such as Copernicus, and high-Ti and low-Ti mare basalts have been mapped on the Moon's surface by telescopic reflectance spectroscopy. The Venusian atmosphere prevents remote-sensed spectral measurements of its surface mineralogy, while atmospheric CO2 and ferric-bearing materials in the regolith on Mars interfere with pyroxene characterization in bright- and dark-region spectra. Reflectance spectral measurements of several meteorite types, including specimens from Antarctica, are consistent with a lunar highland origin for achondrite ALHA 81005 and a martian origin for shergottite EETA 79001, although source regions may not be outermost surfaces of the Moon and Mars. Correlations with asteroid reflectance spectra suggest that Vesta is the source of basaltic achondrites, while wide ranges of olivine/pyroxene ratios are inconsistent with an ordinary-chondrite surface composition of many asteroids. Visible-near-infrared spectrometers are destined for instrument payloads in future spacecraft missions to neighbouring solar system bodies.

Description: Manganese nodules have attracted considerable attention in recent years as a potential source of Mn, Fe, Co, Ni, Cu and other minor elements. These elements are enriched in manganese nodules relative to igneous rocks, sea-water, and deep-sea clays. The present paper describes methods by which element correlations may be determined with the electron-probe, and summarizes the results obtained by electron-beam scanning and specimen traversing. The results obtained in the present electron-probe investigation of manganese nodules may be summarized as follows: (l) The iron concentration fluctuates whereas the manganese concentration is relatively uniform throughout a manganese nodule, hbing slightly higher where iron is low. (2) There is a distinct correlation between Fe, Co, Ti, and Ca. (3) There is pronounced element coherence between Xi, Cu, Zn, and Mg, and between K and Ba. These elements are enriched with Mn and Al in regions of a nodule where the iron concentration is low. (4) The pronounced inter element relationships suggest that isomorphic substitution is an important factor controlling minor element distribution in manganese nodules. The ions Ni2+. Cu2+, Zn2+, Mg2+, K+ and Ba2+ substitute for Mn2+ in the "manganite" phases, Co(III) occurs with Fe(III) in hydrated iron oxide phases and Ti(IV) in delta-MnO2.