Spectral Analyses of ALH 84001, a Meteorite From Mars
Abstract
ALH84001 has recently been reclassified as a meteonte 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 ALH84001 as a chip and as a powder, dry sieved to < 125 micrometers to compare with previous spectral analyses of SNC's and remote observations of Mars. Spectra of the chip and powder in the visible to near infrared region are shown in Figure 1. These spectra are composites of data measured with the RELAB bidirectional spectrometer from 0.3 to 2.55 micrometers 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 micrometer and 2 micrometers are characteristic of low calcium pyroxene and have band rninima of 0.925 micrometers and 1.930 micrometers. The strong absorption near 3 micrometers is characteristic of water. There is a distinct flattening in the spectrum between 1.0 and 1.5 micrometers indicating the presence of an additional absorption. This is interpreted to be the result of Fe^2+ in the M1 site of low calcium 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 include a doublet reststrahlen peak near 1100 cm^-1, and peaks near 880 and 500 cm^-1, which are typical for low calcium pyroxenes. Weaker features at 940 to 1000 cm^-1, 600 to 750 cm^-1, and 530 to 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. Fig. 1., which appears here in the hard copy, shows VIS/NIR reflectance spectra of ALH 84001.92. Fig. 2., which appears here in the hard copy, shows Mid-Ir Reflectance Spectra of ALH 84001.92.
- Publication:
-
Meteoritics
- Pub Date:
- July 1994
- Bibcode:
- 1994Metic..29R.444B
- Keywords:
-
- Chassignites;
- Chemical Composition;
- Meteoritic Composition;
- Mineralogy;
- Nakhlites;
- Shergottites;
- Spectral Reflectance;
- Absorption Spectra;
- Infrared Spectra;
- Mars (Planet);
- Spectrum Analysis;
- Astrophysics;
- METEORITES;
- MARS; ORTHOPYROXENE; SPECTROSCOPY;
- REFLECTANCE