The reflectance spectra of minerals are studied as a function of spectral resolution in the range from 0.2 to 3.0 μm. Selected absorption bands were studied at resolving powers (λ/Δλ) as high as 2240. At resolving powers of approximately 1000, many OH‐bearing minerals show diagnostic sharp absorptions at the resolution limit. At low resolution, some minerals may not be distinguishable, but as the resolution is increased, most can be easily identified. As the resolution is increased, many minerals show fine structure, particularly in the OH‐stretching overtone region near 1.4 μm. The fine structure can enhance the ability to discriminate between minerals, and in some cases the fine structure can be used to determine elemental composition. For example, in amphiboles and talcs, four absorption bands are observed in the samples analyzed in this study that are due to hydroxyl linked to Mg3, Mg2Fe, MgFe2, and Fe3 sites. The band intensities have been shown by other investigators to give the Fe:Fe+Mg ratio from transmission spectra. This study shows that the same equations can be used to obtain the ratio from reflectance spectra of unprepared samples. High‐resolution reflectance Spectroscopy of minerals may prove to be a very important tool in the laboratory, in the field using field‐portable spectrometers, from aircraft, and from satellites looking at Earth or other planetary surfaces.

We have developed a digital reflectance spectral library, with management and spectral analysis software. The library includes 498 spectra of 444 samples (some samples include a series of grain sizes) measured from approximately 0.2 to 3.0 /im. The spectral resolution (Full Width Half Maximum) of the reflectance data is < 4 nm in the visible (0.2-0.8 /im) and < 10 nm in the NIR (0.8-2.35 /im) . All spectra were corrected to absolute reflectance using an NIST Halon standard. Library management software lets users search on parameters (e.g. chemical formulae , chemical analyses, purity of samples, mineral groups, etc.) as well as spectral features.Minerals from borate, carbonate, chloride, element, halide, hydroxide, nitrate, oxide, phosphate, sulfate, sulfide, sulfosalt, and the silicate (cyclosilicate, inosilicate, nesosilicate, phyllosilicate, sorosilicate, and tectosilicate) classes are represented. X-Ray and chemical analyses are tabulated for many of the entries, and all samples have been evaluated for spectral purity. The library also contains end and intermediate members for the olivine, garnet, scapolite, montmorillonite, muscovite, jarosite, and alunite solid-solution series. We have included representative spectra of ELO ice, kerogen, ammonium-bearing minerals, rare-earth oxides, desert varnish coatings, kaolinite crystallinity series, kaolinite-smectite series, zeolite series, and an extensive evaporite series.Because of the importance of vegetation to climate-change studies we have include 17 spectra of tree leaves, bushes, and grasses.The library and software are available as a series of U.S.G.S. Open File reports. PC user software is available to convert the binary data to ascii files (a separate U.S.G.S. open file report). Additionally, a binary data files are on line at the U.S.G.S. in Denver for anonymous ftp to users on the Internet. The library search software enables a user to search on documentation parameters as well as spectral features. The analysis system includes general spectral analysis routines, plotting packages, radiative transfer software for computing intimate mixtures, routines to derive optical constants from reflectance spectra, tools to analyze spectral features, and the capability to access imaging spectrometer data cubes for spectral analysis. Users may build customized libraries (at specific wavelengths and spectral resolution) for their own instruments using the library software.We are currently extending spectral coverage to 150 /im. The libraries (original and convolved) will be made available in the future on a CD-ROM.-15 - THE SPECTRAL LIBRARYThe spectral library contains spectra of 423 minerals, 17 plants and some miscellaneous materials (Table 1, 2, and 3). In some cases, several spectra were measured to span a solid solution series and/or a grain size series. We tried to include spectra of all mineral classes, particularly those important to imaging spectroscopy remote sensing. In other cases, we have studied particular solid solution series because we are mapping t...

Using high-resolution visible and near-infrared diffuse spectral reflectance, we have systematically investigated apparent wavelength shifts as a function of mineral chemistry in the Fe/Mg olivine series from Foil to Fo91. The study also shows that trace amounts of nickel can be spectrally detected in the olivine structure. We show that significant compositional information can only be extracted at relatively high resolution, because the overall spectral characteristics of the olivines change only subtly as a function of the Fe/Mg ratio. Significant spectral variation as a function of grain size is also demonstrated, adding a further complication to the interpretation of remotely sensed data from olivine-rich surfaces. This laboratory study is expected to aid in the interpretation of remotely sensed data from both terrestrial and extraterrestrial bodies. Terrestrial applications may include the recognition of ultramafic, ultrabasic, and basaltic terrains which in themselves may have mineral potential. Among extraterrestrial applications, the asteroids are obvious candidates for further examination if instrumentation can provide the necessary wavelength coverage, resolution, and signal-to-noise ratio so that spectra can be compared to those laboratory data discussed here. Some permutations of Fe-Mg-Ni relations in olivines are discussed as they apply to the interpretation of asteroid surfaces and other extraterrestrial bodies. CRYSTALLOGRAPHIC CONSIDERATIONS The olivine group of minerals is a closely related group of silicates with orthorhombic symmetry [Deer et al., 1982]. The structure of all the minerals of the group consist of independent SiO44-tetrahedra linked by divalent atoms in sixfold coordination. Silicon is not replaced by aluminum, the octahedral positions are almost exclusively filled by divalent ions, Paper number 7B4004. 0148-0227/87/007 B-4004 $05.00 and the trivalent ions Fe +3 and A1 +3 are either absent or present in only trace amounts [Deer et al., 1982]. The olivines studied in this investigation are members of the forsteritc (Mg2SiO4) fayalite (Fe2SiO4) solid solution series' therefore the octahedral positions are filled dominantly by Fe +2 and Mg +2 The ideal structure of forsterite, determined by Bragg and Brown [1926], is characterized by individual silicon-oxygen tetrahedra linked by magnesium atoms each with six nearestneighbor oxygens. The silicon-oxygen tetrahedra point in alternate directions in the X-Y plane, with one half of the octahedral voids filled by either Fe or Mg atoms and one eighth of the tetrahedral voids filled by Si atoms [Bragg and Brown, i•20]. I ne oiivines depart from ideal hexagonal ciosest packing and exhibit two distinct types of polyhedra, designated the M1 and M2 sites [Birle et al., 1968]. According to Deer et al. [1982], the M1 polyhedron is flattened along a threefold axis, whereas the M2 polyhedron is less regular and does not approximate any particular distortion model. However, according to Lumpkin and Ribbe [1983] and Princivalle and Secco [1985-1, the ...

The present laboratory study using high‐resolution reflectance spectroscopy (0.25–2.7 μm) focuses on two primary phyllosilicate groups, serpentines and chlorites. The results show that it is possible to spectrally distinguish between isochemical end‐members of the Mg‐rich serpentine group (chrysotile, antigorite, and lizardite) and to recognize spectral variations in chlorites as a function of Fe/Mg ratio (∼8–38 wt % Fe). The position and relative strength of the 1.4‐μm absorption feature in the trioctahedral chlorites appear to be correlated to the total iron content and/or the Mg/Si ratio and the loss on ignition values of the sample. Spectral differences in the 2.3‐μm wavelength region can be attributed to differences in lattice environments and are characteristic for specific trioctahedral chlorites. The 1.4‐μm feature in the isochemical Mg‐rich serpentines (total iron content ∼1.5–7.0 wt%) show marked spectral differences, apparently due to structural differences.

Spectra obtained from recent telescopic observation of 1-Ceres and laboratory measurements and theoretical calculations of three component mixtures of Ceres analog material suggest that an ammoniated phyllosilicate is present on the surface of the asteroid, rather than H 2 O frost as had been previously reported. The presence of an ammoniated phyllosilicate, most likely ammoniated saponite, on the surface of Ceres implies that secondary temperatures could not have exceeded 400 kelvin.