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.

2.0 Introduction 3.0 Experimental Technique 3.1 Sample Acquisition and Preparation 3.2 Sample Characterization 3.3 Acquisition of Spectra 3.4 Data Storage and Retrieval 4.0 Discussion of Spectra 4.1 Major Spectral Features of Minerals 4.2 Effect of Particle Size 4.21 Role of surface and volume scattering 4.22 Changes in spectral contrast 4.23 Transparency peaks 4.24 Christiansen frequency 4.3 Effect of Crystal!ographic Orientation 4.4 Effect of Packing 4.5 Effect of Atmospheric Gases 4.6 Effect of Impurities 4.7 Using Laboratory Spectra to Predict Remote Sensing Measurements 5.0 Acknowledgements 6.0 Appendix 1: Mineral spectra and description sheets are presented in alphabetical order. Minerals are listed alphabetically and by mineral class, subclass and group at the beginning of the appendix.

Abstract--Junction probability diagrams show variation in both composition and layer arrangement in mixed-layer clay minerals. These diagrams can represent short-range and long-range ordered, random, and segregated interstratifications. Mineralogical analyses ofillite/smectite from shale cuttings, bentonites, and hydrothermally altered tufts define characteristic reaction pathways through these diagrams. Shale and bentonite analyses fall along pathways joining smectite and illite on diagrams showing nearestneighbor (R1) layer arrangements. Transition from random to Rl-ordered interstratifications occurs in shale samples containing 60-70% illite layers, and in bentonites containing 55-67% illite layers. Analyses of alteration products, however, fall near a line connecting rectorite and illite, which represents the maximum degree of R1 layer ordering. No mineralogical evidence is available to suggest that these alteration samples formed from a smectite precursor. All samples develop next-nearest (R2) and thriceremoved (R3) neighbor ordering along similar pathways. Transition to R2 ordering occurs gradually in samples composed of 65-80% iUite layers, and samples containing more than 85% illite layers may show strong R3 ordering.

Abstract--Near-infrared (NIR) reflectance spectra for mixtures of ordered kaolinite and ordered dickite have been found to simulate the spectral response of disordered kaolinite. The amount of octahedral vacancy disorder in nine disordered kaolinite samples was estimated by comparing the sample spectra to the spectra of reference mixtures. The resulting estimates are consistent with previously published estimates of vacancy disorder for similar kaolin minerals that were modeled from calculated X-ray diffraction patterns. The ordered kaolinite and dickite samples used in the reference mixtures were carefully selected to avoid undesirable particle size effects that could bias the spectral results.NIR spectra were also recorded for laboratory mixtures of ordered kaolinite and halloysite to assess whether the spectra could be potentially useful for determining mineral proportions in natural physical mixtures of these two clays. Although the kaolinite-halloysite proportions could only be roughly estimated from the mixture spectra, the halloysite component was evident even when halloysite was present in only minor amounts. A similar approach using NIR spectra for laboratory mixtures may have applications in other studies of natural clay mixtures.

High-resolution solid-state silicon-29 nuclear magnetic resonance spectroscopy using "magic-angle" sample-spinning can readily detect the presence of the high pressure silica polymorphs coesite and stishovite in whole-rock samples from a Meteor Crater, Arizona, impact sample, and yields accurate coesitelstishovite ratios. Such determinations are being carried out by partially suppressing (saturating) intense quartz signals (which have long spinlattice relaxation times) by means of short experimental recycle-times. This method enhances the signal-to-noise ratios of coesite and stishovite (which have relatively short spin-lattice relaxation times). For the sample examined, the coesitelstishovite ratio is about 27.