Icarus 172 (2004) 233–254 www.elsevier.com/locate/icarus Mafic silicate mapping on Mars: effects of palagonitic material, multiple mafic silicates, and spectral resolution Edward A. Cloutis a,∗ , James F. Bell III b a Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB, Canada R3B 2E9 b Department of Astronomy, Cornell University, 402 Space Sciences Building, Ithaca, NY 14853-6801, USA Received 14 November 2003; revised 20 April 2004 Available online 4 August 2004 Abstract The visible to near-infrared spectral reflectance properties of intimate and areal pyroxene + palagonitic material mixtures as well as pure mafic silicates (low-calcium pyroxene, high-calcium pyroxene, pigeonite, olivine) and mixtures of these minerals were analyzed at high spectral resolution (5 nm) as well as with non-contiguous band passes equivalent to recent HST observations and the Pathfinder IMP in order to determine the quality and quantity of mineralogical information (end member compositions, abundances, and grain sizes) derivable in the presence of palagonitic material. In the case of pyroxene + palagonitic material mixtures, pyroxene is detectable at abundances as low as 10 wt%, and its composition can be constrained because (a) its diagnostic absorption feature (located near 1000 nm) persists even for high palagonitic material abundances, and (b) palagonitic material does not appreciably alter the wavelength position of this band (< 4 nm variation). For broad band data (such as Pathfinder IMP band passes), different mafic silicates can be discriminated and palagonitic material abundances constrained using a variety of reflectance ratios and three-point “absorption band depths.” However, other properties of mafic silicate ± palagonitic material assemblages, such as mafic silicate major element compositions, grain sizes, and end member abundances, generally cannot be rigorously quantified. The use of multiple reflectance ratios can, however, be used to identify relative changes in these properties, as most changes in mafic silicate ± palagonitic material assemblage properties are characterized by a unique corresponding set of reflectance ratio variations. The observed spectral-assemblage property trends are consistent with those expected from the known spectral properties of the end members.  2004 Elsevier Inc. All rights reserved. Keywords: Mars surface; Regoliths; Mineralogy; Spectrophotometry 1. Introduction Pyroxenes are among the most widespread mafic sili- cates in the inner Solar System (e.g., McCord et al., 1970; McCord and Clark, 1979; Feierberg et al., 1980; Basaltic Volcanism Study Project, 1981; Dodd, 1981; Surkov et al., 1983; Huguenin, 1987; Cruikshank et al., 1991; Gaffey et al., 1993a, 1993b; McSween and Treiman, 1998) and one of the most well-characterized minerals spectrally (e.g., Adams, 1974; Hazen et al., 1978; Cloutis and Gaffey, 1991a). A knowledge of the compositional, structural, and * Corresponding author. Fax: (204)-774-4134. E-mail address: e.cloutis@uwinnipeg.ca (E.A. Cloutis). textural properties of mafic silicate-bearing assemblages can provide important constraints on the formation con- ditions of targets in which these minerals reside (e.g., Wood and Banno, 1973; Morse, 1980; Lindsley, 1983; Lindsley and Andersen, 1983). Pyroxenes are thought to be widespread on the surface of Mars on the basis of spectral studies (e.g., Singer, 1985; Pinet and Chevrel, 1990; Mustard et al., 1993b; Roush et al., 1993; Bell, 1996; Christensen et al., 1998, 2000; Bandfield et al., 2000; Morris et al., 2000) and known to be present from direct examination of martian meteorites (e.g., Wood and Ashwal, 1981; McSween and Treiman, 1998; Folco et al., 1999). Spectral deconvolution has been success- fully applied to martian meteorite spectra to derive mafic 0019-1035/$ – see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.icarus.2004.06.002