SPECTRAL ANALYSES OF ALH 84001, A METEORITE FROM MARS.  J. Bishop1, C. Pieters1, J. Mustard1, S. Pratt1, and T. Hiroi2, 1 Brown University, Providence RI 02912, USA, 2 NASA Johnson Space Center, Houston TX 77058, USA.

Published in Meteoritics, 29, pp. 444-445.

ALH 84001 has recently been reclassified as a meteorite from Mars (SNC) and contains > 90% orthopyroxene with minor chromite and accessory phases of augite, maskelynite, and carbonate [1]. This meteorite represents a new class of igneous material from Mars. We have measured reflectance spectra of ALH 84001 as a chip and as a powder, dry sieved to <125 µm to compare with previous spectral analyses of SNCs and remote observations of Mars.

Spectra of the chip and powder in the visible-to-near-infrared region are shown in Fig. 1. These spectra are composites of data measured with the RELAB bidirectional spectrometer from 0.3 to 2.55 µm and a Nicolet FTIR for longer wavelengths. As expected, the spectra of the chip have negative slopes and are significantly darker than the spectrum of the particulate sample, which has a positive slope. The strong absorptions near 1 µm and 2 µm are characteristic of low-Ca pyroxene and have band rninima of 0.925 µm and 1.930 µm. The strong absorption near 3 µm is characteristic of water. There is a distinct flattening in the spectrum between 1.0 and 1.5 µm indicating the presence of an additional absorption. This is interpreted to be the result of Fe2+ in the M1 site of low-Ca pyroxene [2].

Mid-infrared spectra showing the Christiansen feature and the reststrahlen bands are shown in Fig. 2 for spectra of the powder and of three different locations on the chip. These spectra exhibit several features in this range, some of which are associated with a specific region on the chip. Each of the spectra includes a doublet reststrahlen peak near 1100 cm-1, and peaks near 880 and 500 cm-1, which are typical for low-Ca pyroxenes. Weaker features at 940-1000 cm-1, 600-750 cm-1, and 530-560 cm-1 are present in spectra from some locations on the chip, but not others, implying compositional and textural variation.

References:  [1] Mittlefehldt D. W. (1994) Meteoritics, 29, 214-221. [2] Besancon J. R. et al. (1991) LPS XXII, 95-96.