A suite of sulfate minerals were characterized spectrally, compositionally, and structurally in order to develop spectral reflectance–compositional–structural relations for this group of minerals.
Edward A. Cloutisa, Frank C. Hawthorneb, Stanley A. Mertzmanc, Katherine Krenna, Michael A. Craiga, Dionne Marcinoa, Michelle Methota, Johnathon Stronga, John F. Mustardd, Diana L. Blaneye, James F. Bell IIIf and Faith Vilasg
aDepartment of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB, R3B 2E9, Canada
bDepartment of Geological Sciences, 335 Wallace Building, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
cDepartment of Geosciences, Franklin and Marshall College, Lancaster, PA 17604-3003, USA
dDepartment of Geological Sciences, Box 1846, Brown University, Providence, RI 02912, USA
eJet Propulsion Laboratory, 4800 Oak Grove Drive, MS183-501, Pasadena, CA 91009, USA
fDepartment of Astronomy, Cornell University, 402 Space Sciences Building, Ithaca, NY 14853-6801, USA
gNASA Johnson Space Center, 2101 NASA Parkway, Code SR, Houston, TX 77058-3696, USA
Received 8 April 2005; revised 29 March 2006.
Available online 24 May 2006.
Abstract
A suite of sulfate minerals were characterized spectrally, compositionally, and structurally in order to develop spectral reflectance–compositional–structural relations for this group of minerals. Sulfates exhibit diverse spectral properties, and absorption-band assignments have been developed for the 0.3–26 μm range. Sulfate absorption features can be related to the presence of transition elements, OH, H2O, and SO4 groups. The number, wavelength position, and intensity of these bands are a function of both composition and structure. Cation substitutions can affect the wavelength positions of all major absorption bands. Hydroxo-bridged Fe3+ results in absorption bands in the 0.43, 0.5, and 0.9 μm regions, while the presence of Fe2+ results in absorption features in the 0.9–1.2 μm interval. Fundamental Ssingle bondO bending and stretching vibration absorption bands occur in the 8–10, 13–18, and 19–24 μm regions (1000–1250, 550–770, and 420–530 cm−1). The most intense combinations and overtones of these fundamentals are found in the 4–5 μm (2000–2500 cm−1) region. Absorption features seen in the 1.7–1.85 μm interval are attributable to Hsingle bondOsingle bondH/Osingle bondH bending and translation/rotation combinations, while bands in the 2.1–2.7 μm regions can be attributed to H2O- and OH-combinations as well as overtones of Ssingle bondO bending fundamentals. OH- and H2O-bearing sulfate spectra are fundamentally different from each other at wavelengths below not, vert, similar6 μm. Changes in H2O/OH content can shift Ssingle bondO band positions due to change in bond lengths and structural rearrangement. Differences in absorption band wavelength positions enable discrimination of all the sulfate minerals used in this study in a number of wavelength intervals. Of the major absorption band regions, the 4–5 μm region seems best for identifying and discriminating sulfates in the presence of other major rock-forming minerals.
Detection and discrimination of sulfate minerals using reflectance spectroscopy (full article)