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Temperature dependencies and thermal dynamical behavior of vibrational phonons related to different bonds/motions (e.g., K-O, Si-O, and Al-O) and O-H stretching, bending, and combinations bands, as well as those of N[H.sub.4] ions, of muscovite have been investigated in detail at high temperatures using in situ infrared spectroscopy. Phonon modes of muscovite show a complex response to heating and dehydroxylation. The mode Gruneisen parameters of muscovite are largest for low-frequency bands and some bands have negative values. Approaching dehydroxylation, bands associated with K-O stretching, Al-OH bending, and Al-O vibrations exhibit significant variations, indicating modifications of local configurations related to these ions. The O-H stretching feature near 3627 [cm.sup.-1] shows a change in temperature dependence of the peak position near or during dehydroxylation, and this is attributed to a dramatic loss of OH and changes in local environments. The infrared spectroscopic analyses carried out in situ or on quenched samples do not record the characteristic bands of dehydroxylation-induced [H.sub.2]O and these findings suggest that [H.sub.2]O is unlikely to be the principal diffusing species. The results suggest that de-ammoniation or loss of N[H.sub.4] in muscovite takes place at temperatures near dehydroxylation. Keywords: Muscovite, infrared spectroscopy, dehydroxylation, high temperature, phonon, hydroxyl DOI: 10.2138/am.2010.3472

The wavelength of the white mica (illite and muscovite) Al-OH absorption band near 2200 nm in 1036 samples from the Belt Supergroup and associated metasedimentary rocks was determined with a portable visible and near infrared reflectance spectrometer. The Al-OH wavelength decreases from 2225 nm in sub-biotite-zone samples to 2194 nm in sillimanite-zone samples; this decrease corresponds with an increase in total Al content of white mica from ~2.0 to ~2.8 atoms per 11 O atoms. These observations indicate that: (1) the frequency of the Al-OH vibration is controlled by the aluminoceladonite exchange reaction [[sup.IV]Si+[sup.VI](Mg,[Fe.sup.2+]) = [sup.IV]Al+[sup.VI]Al], and (2) the reaction proceeds toward more Al-rich composition with increasing metamorphic grade. In these circumstances, Al-OH wavelength provides an indirect monitor of compositional variation and metamorphic grade. Metamorphic grade in most of the study area is in the biotite zone or lower, yet Al-OH wavelengths in low-grade rocks define systematic patterns that correlate with depth of burial and later structural displacements. In higher grade areas, wavelengths generally decrease from the garnet isograd through the sillimanite zone; however, anomalies occur locally, and it is not clear whether these result from differences in bulk composition and mineral assemblage or whether they point to actual metamorphic or structural discontinuities. These findings indicate that reflectance spectroscopy can yield valuable information on metamorphic intensity in rocks containing white mica, particularly in low-grade sequences where conventional indicators of metamorphic grade are lacking. Furthermore, this information can be obtained with field-portable spectrometers and the potential exists to obtain comparable results from airborne and spaceborne imaging spectrometers. Keywords: Belt Supergroup, metamorphism, visible and near infrared spectroscopy, white mica, muscovite, illite, Idaho, Montana, low-grade metamorphism, burial metamorphism DOI: 10.2138/am.2010.3281

We present density functional calculations of vibrational frequencies of OH groups on an idealized goethite (110) surface, represented by a large embedded cluster model. The calculations show that isolated surface groups bound to one, two, and three metal ions can have nearly identical OH stretching frequencies. This finding provides a strong constraint on interpretations of infrared spectra of oxide surfaces, and resolves a long-standing problem in OH vibrational assignments on goethite surfaces, where, in general, too few peaks have been observed relative to the expected heterogeneity of surface functional groups. Keywords: IR spectroscopy, quantum mechanical calculations, surface studies, goethite, iron oxide DOI: 10.2138/am.2010.3302

There are four ways by which OH commonly substitutes into olivine, namely those associated with (1) Si vacancies, (2) Mg vacancies, (3) Ti, or (4) trivalent cations. The four mechanisms, which we label [Si], [Mg], [Ti], and [triv], respectively, may each be fingerprinted by their characteristic O-H stretching modes in the infrared spectrum. We show by comparing the integrated intensities of these characteristic infrared peaks against total water content analyzed by secondary ion mass spectrometry, obtained for a suite of synthetic olivines plus one natural olivine, that the different substitution mechanisms require different absorption coefficients (k). For [Ti], we find k = 0.18 [+ or -] 0.07, identical to the value previously obtained from natural olivines in which the water was mainly associated with [Ti] defects. Values of k for [Si] and [triv] are 0.57 [+ or -] 0.04 and 0.18 [+ or -] 0.05, respectively; that for [Mg] is too small to be accurately determined (0.03 [+ or -] 0.03). The values of k for [Ti] and [Si] defects differ by a factor of three even though their average wavenumbers are virtually the same. The [Ti] and [triv] defects, on the other hand, have very similar absorption coefficients at significantly different wavenumbers. This highlights the inadequacy of using wavenumber-dependent calibrations for olivine and presumably for NAMs in general. Different substitution mechanisms have their own crystallographic environments that determine their absorption coefficients. The large variation in absorption coefficients within a single mineral emphasizes the importance of distinguishing the substitution mechanism if meaningful quantitative results are to be obtained from infrared spectroscopy. Keywords: Nominally anhydrous minerals, olivine, infrared spectroscopy, secondary ion mass spectrometry, extinction coefficients DOI: 10.2138/am.2010.3313

Mid-IR spectra (4000-400 [cm.sup.-1]) of synthetic calcic amphiboles in the tremolite-pargasite series and of various natural calcic amphiboles have been investigated. The pargasite substitution, a combination of the Tschermak (=[sup.4][Al.sup.[6]][Al.sup.[6]][Mg.sub.-1][sup.[4][Si.sub.-1]) and edenite (=[sup.[4][Al.sup.[A]][Na.sup.[4]][Si.sub.-1][sup.[A][equivalent.sub.-1]) substitutions, causes the following features in the region 1200-600 [cm.sup.-1]. (1) Weak [sup.[4]]Al-O stretching bands appear at 895 and 815 [cm.sup.-1] that are distinct from the 955 and 925 [cm.sup.-1] Si-O stretching bands in tremolite. (2) There is a reduction in the intensity and frequency of the Si-O-Si symmetric bending band (='chain breathing' mode) at 750 [cm.sup.-1] in tremolite, and there is an appearance of medium-strong composite bands having a weak shoulder on the high-frequency side near 690 [cm.sup.-1]. These bands are assigned to Si-O-Al deformation bands. (3) Two OH-libration bands at 690 and 650 [cm.sup.-1] become weak and broad composite bands from 720 to 610 [cm.sup.-1]. And (4) because the intensity and frequency of the band at 640 [cm.sup.-1] in tremolite is affected neither by deuteration nor by the pargasite substitution, this band is ascribed to O-[sup.[T2]]Si-O bending. Even in pargasite, most T2 sites are occupied by Si, so that the O2-[sup.[T2]]Si-O4 bending mode will be dominant in this amphibole. The same behavior occurs for the synthetic fluoro-gallian tremolite-pargasite series but with larger downward frequency shifts--Ga-O stretching bands appear at 880 and 780 [cm.sup.-1], and an Si-O-Ga bending band appears at 605 [cm.sup.-1]. The major T-O-T and O-T-O deformation bands in synthetic amphiboles are readily apparent in natural calcic amphiboles whose compositions are near the tremolite-pargasite join. Keywords: Mid-IR, calcic amphibole, tremolite, pargasite, deuteration

The theoretical infrared spectrum of hematite ([alpha]-[Fe.sub.2][O.sub.3]) was computed using ab initio quantum mechanical calculations. Frequencies of the normal vibrational modes and Born effective charges were computed using the density functional theory (DFT) with and without the addition of a Hubbard U correction. The infrared reflection spectra of a single crystal of hematite were calculated as well as the infrared powder absorption spectrum using an electrostatic model that takes into account the shape of hematite particles. The theoretical behavior of the absorption bands is in agreement with experimental observations and provides a firm basis for the interpretation of the bands in term of vibrational modes. Overall, results suggest that the use of DFT + U, which is necessary to describe correctly the electronic and magnetic properties of hematite, does not improve noticeably the prediction of vibrational properties. Keywords: Iron oxide, density functional theory, infrared spectroscopy

We report on temperature dependencies of infrared (IR) fundamental, combination, and overtone vibrations of hydroxyl species (OH) in nominally anhydrous minerals (e.g., titanite), ferroelectric crystals (K[Ta.sub.1] [sub.x][Nb.sub.x][O.sub.3], KTN), layer silicates (talc, mica, and pyrophyllite), and hydrous minerals such as apatite and synthetic hydrous/deuterated garnets [[Ca.sub.3][A1.sub.2][([O.sub.4][H.sub.4]).sub.3] and [Ca.sub.3][Al.sub.2][([O.sub.4][D.sub.4]).sub.3]] for the temperature range of 20-300 K. Data obtained by high- resolution FTIR spectroscopy show that increasing temperature generally leads to a decrease in the band height and band area of fundamental vibrations of hydroxyl species, whereas the combination and first-overtone bands commonly show different temperature dependencies. The results show that in the investigated temperature range, the variations of the band height and area for different OH bands (especially for combinations and overtones) on cooling or heating do not reflect changes in OH concentrations in the materials, but relate to temperature-dependent absorption coefficients. The observations imply that absorption coefficients calibrated at room temperature cannot necessarily be used for the determination of hydroxyl contents at other temperatures. Keywords: Infrared spectroscopy, low temperature, apatite, hydrous garnet, pyrophyllite, tale, sericite, titanite

New measurements of thermal infrared emission spectra (250-1400 [cm.sup.-1]; ~7-40 [micro]m) of experimentally shocked basalt and basaltic andesite (17-56 GPa) exhibit changes in spectral features with increasing pressure consistent with changes in the structure of plagioclase feldspars. Major spectral absorptions in unshocked rocks between 350-700 [cm.sup.-1] (due to Si-O-Si octahedral bending vibrations) and between 1000-1250 [cm.sup.-1] (due to Si-O antisymmetric stretch motions of the silica tetrahedra) transform at pressures >20-25 GPa to two broad spectral features centered near 950-1050 and 400-450 [cm.sup.-1]. Linear deconvolution models using spectral libraries composed of common mineral and glass spectra replicate the spectra of shocked basalt relatively well up to shock pressures of 20-25 GPa, above which model errors increase substantially, coincident with the onset of diaplectic glass formation in plagioclase. Inclusion of shocked feldspar spectra in the libraries improves fits for more highly shocked basalt. However, deconvolution models of the basaltic andesite select shocked feldspar end-members even for unshocked samples, likely caused by the higher primary glass content in the basaltic andesite sample. Keywords: Shock, infrared, spectroscopy, basalt, deconvolution, Mars

The local mixing and ordering behavior of the otavite-magnesite solid solution has been characterized using infrared powder absorption spectroscopy in the spectral region 50-2000 [cm.sup.-1] at room temperature. Lattice modes due to Cd translations (75-200 [cm.sup.-1]) and Mg translations (200-350 [cm.sup.-1]) were both observed in the IR spectra for samples of intermediate composition. Peak positions of Cd translations remain constant as a function of composition, whereas those of Mg translations decrease in wavenumber with increasing otavite content. This suggests that the otavite-magnesite solid solution displays a combination of one-mode and two-mode behavior, most likely due to the large difference in atomic weight between magnesium and cadmium. Vibrational bands relating to the C[O.sup.2-.sub.3] groups in the spectral region 600-900 [cm.sup.-1] vary linearly as a function of composition and are not sensitive to the degree of order. The vibrational band at ~1400-1450 [cm.sup.-1] also varies linearly with composition, but R[bar.3] ordered samples show a marked increase in frequency compared to their R[bar.3]c counterparts. Positive deviations from linearity are observed for the effective line width determined using the autocorrelation method (expressed in terms of [DELTA]corr values) for both lattice modes and bending vibrations of the C[O.sup.2-.sub.3] molecular groups, whereas a linear variation as a function of composition of the [DELTA]corr values of the C[O.sup.2-.sub.3] stretching mode is observed for the 800 [degrees]C solid solution. Only in the region 600-900 [cm.sup.-1] is an effect of order observed as a reduction in [DELTA]corr values with respect to the sample with R[bar.3]c symmetry. The difference in [DELTA]corr values between the ordered and disordered samples was used to determine the local order parameter, q, which is consistent with a tricritical order-disorder transition. Keywords: IR spectroscopy, otavite-magnesite solid solution, autocorrelation, phase transition, carbonates.

Crystallization experiments were conducted at 200 MPa and water-undersaturated conditions to quantify the effect of small amounts of [H.sub.2]O on the crystallization temperature of olivine in basaltic melts (e.g., Mid-Oceanic Ridge Basalts, MORB).The [H.sub.2]O concentrations in the quenched glasses, determined by infrared spectroscopy and Karl-Fischer-Titration, ranged between 0.25 and 4.2 wt% [H.sub.2]O. The dry liquidus temperature was estimated from experiments at 0.1 MPa ([H.sub.2]O-free) and from the known pressure dependence of olivine crystallization temperature. The liquidus temperature depression can be predicted by the empirical equation ([T.sup.DRY]-[T.sup.WET]) = 39.69*[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (wt%). The comparison of the experimental results with available crystallization models and empirical methods shows that most of the predicted liquidus temperature depressions differ significantly from that observed in this study. Keywords: Crystallization, [H.sub.2]O, MORB, olivine, liquidus, FTIR, KFT

Experiments in the system [K.sub.2]O-[(N[H.sub.4]).sub.2]O-[Al.sub.2] [O.sub.3]-Si[O.sub.2]-[H.sub.2]O-HCl have been conducted between temperatures of 400 and 600 [degrees]C at pressures of 200, 400, 500, and 1500 MPa. The run products consisted of solid solutions of the K-feldspar-buddingtonite, muscovite-tobelite series, and quartz. The run products were characterized by electron microprobe, powder X-ray diffraction with Rietveld analysis, and infrared spectroscopy. It can be shown that complete solid solution exists for both series for temperatures at least above 400 [degrees]C. The grain size of the synthesized phases was usually small and rarely exceeded 10 gm. In addition the micas were quite thin and the thickness was lower than 100 nm. Due to the small grain size and the [(N[H.sub.4]).sub.2]O-content, reliable electron-microprobe results were difficult to obtain. Rietveld analyses did show that the synthesized micas consisted of a complex mixture of 1M, 2M1, 2M2, 3T, and 20r polytypes. The lattice parameters of the feldspar and mica solid solutions are linear combinations of the end-members and show practically no excess volume. Reasonable compositions of the solid solutions can be derived from the lattice parameters. The mica solid solutions are not binary mixtures but at elevated pressure increasing amounts of pyrophyllite component were observed. By using the N[H.sub.4]-deformation mode at around 1430 [cm.sup.-1] and the OH-stretching vibrations [V.sub.OH], at 3600-3700 [cm.sup.-1] the N[H.sub.4]-contents of the micas could be determined also by IR spectroscopy. Keywords: Chemical analysis, K-N[H.sub.4] feldspar, mica, IR spectroscopy, experimental petrology, feldspar

Mid-infrared thermal emission spectra were acquired and are presented for 37 different sulfate minerals representing Strunz classes 6/A-D as well as a few other miscellaneous sulfate-bearing minerals (Strunz class 3/C and 8/J). Sulfate vibrational modes are assigned to each spectrum; also assigned are the modes of component OH, [H.sub.2]O, and carbonate where applicable. A discussion also is presented regarding the effect of hydration state on the emissivity spectra; dehydration of the Ca-sulfate mineral series (e.g., gypsum-bassanite-anhydrite), as well as the Mg-sulfate series, causes the high-frequency edge of the sulfate [v.sub.3] band to shift to a larger wavenumber. Keywords: Mid-infrared, vibrational, spectroscopy, emissivity, emission, sulfate, spectra

Four colorless tourmalines of the liddicoatite-elbaite series from pegmatites from Anjanabonoina, Madagascar, have been characterized by crystal-structure determination and by chemical analyses. Optimized formulae range from [sup.X]([Ca.sub.0.57][Na.sub.0.29][??]0.14) [sup.Y]([Al.sub.1.41][Li.sub.1.33][Mn.sup.2+.sub.0.07][??]0.19) [sup.Z][Al.sub.6][sup.T]([Si.sub.5.86][B.sub.0.14])[O.sub.18] [(B[O.sub.3]).sub.3][sup.V][(OH).sub.3.00] [sup.W][F.sub.0.76] [(OH).sub.0.24]] [a = 15.8322(3), c = 7.1034(3) [Angstrom]] to [sup.X]([Na.sub.0.46][Ca.sub.0.30[??]0.24) [sup.Y]([Al.sup.1.82][Li.sub.0.89][Fe.sup.2+.sub.0.01] [Mn.sup.2+.sub.0.01[??]0.27) [sup.Z][Al.sub.6] [sup.T]([Si.sub.5.56] [B.sub.0.44])[O.sub.18] [(B[O.sub.3]).sub.3] [sup.V][(OH).sub.3.00] [sup.W][[(OH).sub.0.50][F.sub.0.50]] [a = 15.8095(9), c = 7.0941 (8) [Angstrom]] (R = 1.3-1.7%). There is a high negative correlation ([r.sup.2] = 0.984) between the bond-lengths (~1.618-1.614 [Angstrom]) and the amount of [sup.IV]B (from the optimized formulae). Similar to the olenites (from Koralpe, Austria) the liddicoatite-elbalte samples show a positive correlation between the Al occupancy at the Y site and [sup.IV]B ([r.sup.2] = 0.988). Short-range order configurations show that the presence of [sup.IV]B is coupled with the occupancy of ([Al.sub.2]Li) and ([Al.sub.2][??]) at the Y site. The structural formulae of the Al-rich tourmalines from Anjanabonoina, Madagascar, show ~[[??].sub.0.2] (vacancies) on the Y site. We believe that short-range order configurations with [sup.Y]([Al.sub.2][??]) are responsible for these vacancies. Hence, an oft-used calculation of the Li content by difference on the Y site may be problematic for Al-rich tourmalines (olenite, elbaite, rossmanite). Fourier transform infrared (FTIR) spectra were recorded from the most [sup.IV]B-rich tourmaline sample. The bands around 5195 and 5380 [cm.sup.-1] can be assigned to [H.sub.2]O. Because these bands still could be observed in FFIR spectra at temperatures from -150 to +600 [degrees]C, it seems unlikely that they result from [H.sub.2]O in fluid inclusions. Interestingly, another FTIR spectrum from a dravite in which the X site is filled completely with Na, does not show bands at ~5200 and ~5400 [cm.sup.-1]. Although not definitive, the resulting spectra are consistent with small amounts of [H.sub.2]O at the X site of the elbalte. The rare-earth element (REE) pattern of the B-rich elbaite ([summation]REE: ~150 ppm) demonstrates that this sample is strongly enriched in LREEs compared to HREEs and exhibits a negative Eu anomaly. This sample shows the strongest enrichment of LREEs and a high [La.sub.N]/[Yb.sub.N] ratio of ~351, which seems to confirm an important role of the fractional crystallization process. Keywords: Liddicoatite-elbaite, tetrahedrally coordinated boron, Madagascar, structure, chemistry

Eight silicate unit vibrational modes were identified in a suite of PbO-Si[O.sub.2] glasses using micro-reflectance Fourier Transform infrared ([mu]R-FTIR) spectra that were transformed using the Kramers-Kronig relation. The transformed FTIR spectra, in the 800-1200 [cm.sup.-1] range, were deconvolved systematically into eight Voigt-shaped bands at centers that were predicted from the second derivative of the spectra. The area of the eight bands varied as a function of Si[O.sub.2] content, and these trends were combined with theoretical constraints to identify and assign the bands to seven provisional silicate units: Si[O.sup.4-.sub.4] (830 and 860 [cm.sup.-1]), [Si.sub.2][O.sup.6-.sub.7] (900 [cm.sup.-1]), [Si.sub.6][O.sup.12-.sub.18] (950 [cm.sup.-1]), [Si.sub.2[O.sup.4-.sub.6] (980 [cm.sup.-1]), [Si.sub.4][O.sup.6-.sub.11] (1010 [cm.sup.-1]), [Si.sub.2][O.sup.2-.sub.5] (1050 [cm.sup.-1]), and Si[O.sub.2] (1100 [cm.sup.-1]). The provisional units were then grouped according to their NBO/T values: NBO/T = 4 (Si[O.sup.4-.sub.4), NBO/T = 3 ([Si.sub.2][O.sup.6-.sub.7), NBO/T = 2 ([Si.sub.6][O.sup.12-.sub.18] and [Si.sub.2][O.sup.4-.sub.6), NBO/T = 1 ([Si.sub.4][O.sup.6-.sub.11] and [Si.sub.2][O.sup.2-.sub.5]) and NBO/T = 0 (Si[O.sub.2]). The derived quantities of each NBO/T unit compare favorably with nuclear magnetic resonance data for PbO-Si][O.sub.2] glasses reported in the literature. This new approach for determining glass structure is advantageous because it may be performed on small Fe-bearing samples with minimal preparation, and analyses are rapid and relatively inexpensive. Keywords: IR spectroscopy, glass structure, band fitting, PbO-Si[O.sub.2]

The OH-structural characteristics of an iron-rich palygorskite from Western Macedonia, Greece (Gr-1) and an aluminous palygorskite from Florida (PF1-1) were examined by combined Fourier-transform near-infrared reflectance (NIR) and mid-infrared attenuated total reflectance (ATR) spectroscopy. Analyses of samples heated from ambient to 130 [degrees]C allowed for the development of a self-consistent set of band assignments for the structural and surface OH and [H.sub.2]O species of both the hydrated and dehydrated forms. The inner octahedral sites of both samples are largely accounted for by dioctahedral AlAlOH, Al[Fe.sup.3+]OH, and [Fe.sup.3+][Fe.sup.3+]OH pairs. Band intensities for these pairs are consistent with variations in the concentration of octahedral Fe and Al in the two samples. In addition, both samples display a trace trioctahedral signature in NIR, which may be related to local trioctahedral domains, or the presence of sepiolite in trace amounts, or as intergrowths. A surface [H.sub.2]O species typical of the hydrated phase was identified via its NIR combination mode at 5317 [cm.sup.-1]. The desorption of this species by heating revealed distinct silanol groups with overtone and combination modes at 7255 and 4575 [cm.sup.-1], respectively. Mg-coordinated and zeolitic [H.sub.2]O species are strongly coupled in the hydrated phase and give rise to NIR combination modes at 5190 and 5240 [cm.sup.-1]. The removal of zeolitic [H.sub.2]O causes the blue shift of the three dioctahedral OH overtones by ca. 20 [cm.sup.-1] and the rearrangement of the coordinated [H.sub.2]O manifested by the growth of sharp combination modes at ca. 5215 and 5120 [cm.sup.-1]. Keywords: IR spectroscopy, palygorskite, NIR spectroscopy, Fe-rich, hormite, hydration

High-resolution transmission-electron microscopy (HRTEM) and infrared spectroscopy (FTIR) analyses have been done on amphiboles near the join tremolite [[Ca.sub.2][Mg.sub.5][Si.sub.8][O.sub.22][(OH).sub.]2 = TR]-pargasite [Na[Ca.sub.2][Mg.sub.4][Al.sub.3][Si.sub.6][O.sub.22] [(OH).sub.2] = PG] in the ternary system tremolite-pargasite-cummingtonite [[Mg.sub.7][Si.sub.][O.sub.22] [(OH).sub.2] = MC] that were synthesized previously by Sharma and Jenkins (1999). Representative samples across the join were examined in detail by HRTEM to document the presence and concentration of chain multiplicity defects (CMFs). There was relatively little change in the defect density with composition, with the tremolitic sample (TREM 23-13) having the highest defect concentration (6%) and the more PG-rich samples having slightly lower CMF concentrations (4-5%). CMFs with multiplicities of 1,3, 4, 5, and 6 were observed, usually as isolated chains, with the most common being triple-chain slabs. Correction of the bulk composition of the tremolitic amphibole for the presence of these Mg-rich, wide-chain defects reduces the MC content from an apparent value of 8.5 to 4-7.5 mol% MC, depending on which composition is used for the triple-chain defect. The entire amphibole join was examined by FTIR spectroscopy in the OH-stretching region (3000-3800 [cm.sup.-1]) for the purpose of determining the presence of short-range order. A total of 10 component bands were fitted to the spectra across the join. These bands were assigned to specific cation configurations on the basis of earlier studies of the FTIR spectra of chemically simplified amphibole joins pertinent to this study. The extent of short-range order was qualitatively determined by comparing the observed intensities for groups of related bands, corrected for differences in their molar absorptivities, to their calculated intensifies based on random-mixing probabilities. From this exercise, it is observed that the intensities of sodic amphibole configurations are consistently high, tremolite is lowest near the middle of the join, and aluminous amphibole configurations cross over from being higher (at low A1 contents) to being lower (at high A1 contents) than expected near the middle of the join. These differences between observed and predicted band intensities may reflect the presence of deviations in the thermodynamic activities of amphibole components from those predicted on the basis of random-mixing models.

Clinopyroxenes in eclogites from the deep subducted crust in the Kokchetav, Kazakhstan, ultra-high-pressure metamorphic terrane were found by infrared spectroscopy to contain up to 3020 ppm OH. These rocks were recrystallized at pressures over 60 kbar and temperatures over 1000[degrees]C, where no hydrous minerals are stable. Infrared spectra of the clinopyroxenes show three hydroxyl absorption bands in the regions 3440-3460 [cm.sup.-1], 3500-3530 [cm.sup.-1], and 3600-3625 [cm.sup.-1]. The hydroxyl absorbance increases with recrystallization pressure of the eclogites and with vacancy concentration in the pyroxene structure (Ca-Eskola component). Clinopyroxenes represent about 40-50 vol% of eclogites, such that the bulk eclogites contain approximately 1300 ppm hydroxyl at depths greater than 150 km. Thus, subducted oceanic crust can transport trace amounts of [H.sub.2]O into the upper mantle, even in the absence of nominally hydrous minerals.

The molecular structures of the basic copper phosphate minerals pseudomalachite, libethenite, and cornetite were studied using a combination of infrared emission spectroscopy, infrared absorption, and Raman spectroscopy. Infrared emission spectra of these minerals were obtained over the temperature range 100 to 1000[degrees]C. The infrared spectra of the three minerals are different, in line with differences in crystal structure and composition. The absorption spectra are similar, particularly in the OH stretching region, but characteristic differences in the bending regions are observed. Differences are also observed in the phosphate stretching and bending regions. The IR emission of the basic copper phosphates studied shows that the minerals are completely dehydroxylated by 550[degrees]C.

Mixed-layer minerals were analyzed by far infrared (FIR) spectrometry. The FIR spectra show two bands, which occur at 84-87 and 108-114 [cm.sup.-1] for mixed-layer illite-smectite (I-S) and at 71-79 and 103 [cm.sup.-1] for mixed-layer phlogopite/vermiculite (P-V). The 103 [cm.sup.-1] band seen in the P-V series from Palabora is independent of [K.sub.+] content and is attributed to lattice vibrations. The lower wavenumber band observed at 85 [cm.sup.-1] for I-S mixed-layers and 71-73 [cm.sup.-1] for P-V mixed-layers corresponds to [K.sup.+] fixed in the two-layer stacking sequences. This low wavenumber band shifts to higher wavenumbers as the thickness of coherent scattering domains increases: shifting toward 97 [cm.sup.-1] for the illite end-member of the I-S series and to 79 cm-~ for Palabora phlogopite, the end-member of the P-V series.

The [Fe.sup.3+]-Al substitution in synthetic zoisite was studied in the system CFASH at 2.0 GPa and 750[degrees]C (compositional range: 0.0-0.14 [X.sub.ps]). The samples were characterized by powder X-ray diffraction, FTIR, and electron microprobe. Discontinuities in refined lattice parameters at N0.05 [X.sub.ps] are attributed to two distinct and hitherto unknown modifications, zoisite I (0.05 [X.sub.ps]. The following lattice parameters were derived: (zoisite I) a ([Angstrom]) = -3.72 x [10.sup.-2] x [X.sub.ps] + 16.1913 b ([Angstrom]) = 6.43 x [10.sup.-2] x [X.sub.ps] + 5.5488 c ([Angstrom]) = 3.43 x [10.sup.-2] x [X.sub.ps] + 10.0320 V ([[Angstrom].sup.3]) = 11.4 x [X.sub.ps] + 901.3 (zoisite II) a ([Angstrom]) = -8.26 x [10.sup.-2] x [X.sub.ps] + 16.2061 b ([Angstrom]) = 8.14 x [10.sup.-2] x [X.sub.ps] + 5.5486 c ([Angstrom]) = 1.18 x [10.sup.-1] x [X.sub.ps] + 10.0263 V ([[Angstrom].sup.3]) = 19.3 x [X.sub.ps] + 901.6 In both modifications, substitution of [Fe.sup.3+] expands the M3 octahedron, resulting in opposed rotations of the corner-linked T1 and T2 tetrahedra of the [Si.sub.2][O.sub.7] group. The extent of rotation is limited and controls the maximum [Fe.sup.3+] content in zoisite I and II. With increasing [Fe.sup.3+] content, zoisite I transforms to zoisite II and zoisite II to clinozoisite. The transformation from zoisite I to II can be classified as a substitutionally induced isosymmetric displacive phase transition. Four significant IR bands were observed at ~3250, ~3195, ~3155, and ~2170 [cm.sup.-1]. The first three bands are attributed to the configurations [Al.sub.2][sup.M1,2]-O10 ... O2-[Al.sub.2][sup.M1.2]([Al,[Fe.sup.3+])[sup.M3], [Al.sub.2][sup.M1,2]-O10H ... O4-[Al.sub.2][sup.M1,2][Fe.sup.3+][sup.M3], and [Al.sub.2][sup.M1,2]-O10-H ... O4-[Al.sub.2][sup.M1,2]Al[sup.M3]. O10-H ... O2 is bifurcated between the two symmetrically arranged O2 and O2' atoms. The band at ~2170 [cm.sup.-1] is interpreted as the first overtone of the bending vibration of O10-H ... O2. In analogy with the results from powder XRD the IR bands show discontinuities at ~0.05 [X.sub.ps], confirming the two modifications of zoisite.

Radiation damage and the recrystallization of natural titanite (CaTiSi[O.sub.5]) were studied using infrared spectroscopy in the spectral range from 50 to 7500 [cm.sup.-1]. The results show that radiation damage leads to systematic changes in spectral features: decreasing absorption and reflectivity, line broadening, and loss of orientational dependence. Strongly damaged titanite shows hydroxylate bands between 2200 and 3500 cm-j. The band most affected by radiation damage is the Ti-O stretching band near 670 [cm.sup.-1]. It shifts to 710 [cm.sup.-1] in the most damaged samples, possibly indicating the presence of Ti[O.sub.5] complexes in metamict titanite. Titanite glasses (quenched melts of CaTiSi[O.sub.5]) show spectral features different from those of radiation-damaged titanite, especially in the Ti-O and Si-O stretching regions. Annealing radiation-damaged titanites at high temperatures results in the recovery of damaged crystalline regions. Recrystallization near 900 K is characterized by an increase in reflectivity, integrated absorbance, and line sharpening. Different infrared bands show recovery at different temperatures. The restoration of the Ti-O stretching band near 670 [cm.sup.-1] and an infrared band near 285 [cm.sup.-1] took place at temperatures of 1200-1400 K. Temperature-induced changes of the OH-absorption bands could be responsible for the previously reported differences in the temperature evolution of infrared spectra of OH species between in situ and quench experiments.

Two suites of garnets were examined by infrared absorption spectroscopy and depolarized Raman spectroscopy to determine if the Raman signal could be used as a quantitative measurement of OH content. To avoid the problems of determining the absolute Raman signal intensity, the integrated intensity of the OH bands was ratioed to the integrated intensity of silicate Si-O stretching bands and used as a proxy for the OH intensity. These were compared to the OH contents, expressed as wt% [H.sub.2]O, independently determined from infrared absorption. A somewhat useful trend developed between OH contents determined by Raman and IR for some grossular garnets with [H.sub.2]O contents less than 0.5%. Many colorless to near-colorless grossular garnets do not provide a useful Raman signal due to fluorescence, although other samples with [H.sub.2]O contents between 0.5 and 1.3 wt% and are strongly colored, fall far below the trend of the samples with lower H20-contents. Spessartine-almandine garnets from the Rutherford no. 2 pegmatite all respond to the Raman experiment, but produce a confusing trend when compared to [H.sub.2]O. Coincidentally, a relatively smooth but decreasing trend was observed when the spessartine Raman OH intensity ratio was compared to the iron content. These observations suggest that Raman measurements by this method are not suitable, in general, for the determination of OH in garnets.

Polarized infrared absorption spectra of thin, oriented single-crystal slabs of pectolite and serandite were recorded between 4000 and 350 [cm.sup.-1] at 298 and 83 K. The spectra of both minerals show a broad absorption region parallel to the silicate chains (b direction) that is centered around 1000 [cm.sup.-1], which is interrupted by a transmission window, and which is superimposed by sharp silicate, lattice, and overtone modes. This band is assigned to the OH stretching mode consistent with the alignment of the O-H O hydrogen bond parallel to b and the short O . . . O distance of 2.45-2.48 [Angstrom] that was found in previous X-ray structure refinements. At 1396 [cm.sup.-1] (pectolite) and 1386 [cm.sup.-1] (serandite) an OH bending mode is observed in the IR spectra parallel to c. At low temperatures, this mode shifts up to higher frequencies (1403 [cm.sup.-1] at 83 K in pectolite), whereas the down-shift of the OH stretching mode cannot be observed due to the extremely broad band width. The slightly higher energy of the bending mode in pectolite indicates a slightly stronger hydrogen bond with respect to serandite. However, the bond length in serandite is slightly shorter than that in pectolite. An asymmetric O-H O bond is confirmed in pectolite and serandite through comparison with different materials with similar, very strong hydrogen bonds and low-energy OH stretching modes.

Using IR absorption data from polarized measurements on single-crystal minerals with stoichiometric water contents (in the form of [H.sub.2]O or OH groups in the structure), a linear calibration curve ([r.sup.2] [equivalent to] 0.98) for water in minerals is established in the form: [[Epsilon].sub.i] (the integrated molar absorption coefficient in units of [cm.sup.-2] per mol [H.sub.2]O/L) = 246.6(3753 v) (v = the mean wavenumber of the OH stretching band [in [cm.sup.-1]). The investigated minerals include hydrogrossular, analcime, hemimorphite and its dehydrated phase, lawsonite, goethite, diaspore, manganite, mozartite, and pectolite. The influence of hydrogen bonding, leading to increased absorption values with lower OH stretching band energies, is confirmed. It is further shown that only the use of integrated absorbance values (band areas) results in a linear correlation with water content, whereas linear absorption data (peak heights) are not correlated. The calibration agrees with previously published quantitative IR data on staurolite and trace H in pyroxenes. It is also close to the frequently used trend of Paterson (1982). However, some of the previous calibrations of trace H in nominally anhydrous minerals, e.g., kyanite and pyrope, differ appreciably from the correlation derived from stoichiometrically hydrous minerals.

An experimental method for the determination of Ab-Or exsolution and Al-Si ordering in alkali feldspar is described. Powder infrared spectroscopy was used to measure spectra in the spectral range between 50 and 1500 [cm.sup.-1] using about 5 mg of sample material. The spectra were analyzed using reference spectra of uniform samples with various Ab-Or compositions and several degrees of Al-Si order. The application of this method is demonstrated for two examples of exsolved feldspar minerals, and it is shown that detailed characterization of alkali feldspars using IR spectroscopy leads to new insight into their structural details.

We report the direct experimental observation of a structural anomaly near 825 K in synthetic and natural titanite samples by high-temperature, hard-mode infrared spectroscopy. The anomaly in titanite, CaTiSi[O.sub.5], is characterized by a break of the temperature dependence of the 562 [cm.sup.-1] Si-O bending mode, the 675 [cm.sup.-1] Ti-O band, and the 900 [cm.sup.-1] Si-O stretching modes, and the rapid decrease of the IR signal at 873 [cm.sup.-1]. The order parameter, as determined from the temperature evolution of the frequencies of the absorption bands in the middle infrared (MIR) region follows a second-order Landau behavior with an order-parameter exponent [Beta] = 1/2. At T > 825 K, the Ti-O band shows further softening, whereas the Si-O bands at 562 and 900 [cm.sup.-1] show hardening with increasing temperature. In natural samples, the effects of impurities on the high-temperature transition are weak. For pure titanite, the transition temperature, [T.sub.c], is about 825 K and increases with increasing impurity concentration.

[Mg.sup.2+]-[Fe.sup.2+] substitution in the dodecahedral interstice of eight natural single crystals and two synthetic polycrystalline garnets was investigated by measurement of mid- and far-infrared (IR) reflectance spectra across the pyrope-almandine [Py-Al = [([Mg.sub.x]-[Fe.sub.1-x]).sub.3][Al.sub.2][Si.sub.3][O.sub.12]] binary. The effect of minor Mn and Ca substitution was investigated by comparison with spectra of four additional natural garnets, [Py.sub.8][Al.sub.82][Sp.sub.10] and [Py.sub.10][Al.sub.76][Sp.sub.14], where Sp denotes spessartine ([Mn.sub.3][Al.sub.2][Si.sub.3][O.sub.12]), and [Py.sub.72][Al.sub.18][Gr.sub.10] and [Py.sub.54][Al.sub.36][Gr.sub.10], where Gr denotes grossular ([Ca.sub.3][Al.sub.2][Si.sub.3][O.sub.12]). Data obtained from the two synthetic polycrystals are in excellent agreement with data from the single crystals. Frequencies of all 17 IR-active fundamental modes were observed in all specimens except pyrope. Of the 17 modes, 16 show linear correlations between frequency and composition along the pyrope-almandine join. The remaining mode, assigned to translations of the divalent cations against the O framework, exhibits two-mode behavior. The trends show that two modes in pyrope are accidentally degenerate. Frequencies of garnets with up to 10 mol% spessartine and grossular contents lie on the trends defined by the pyrope-almandine samples with negligible impurities. However, one to three additional modes are seen for some intermediate compositions, apparently resulting from either resonances among combination modes or two-mode behavior due to high Ca contents. The nearly linear behavior of the modes indicates that mixing should be close to ideal for the pyrope-almandine series because the lattice contribution dominates heat capacity, entropy, and compressibility.

Two structurally related magnesium phosphates, phosphoellenbergerite ([P6.sub.3]mc) and holtedahlite ([P6.sub.3]), have been investigated using a combination of high-frequency IR and 1H MAS, 31P MAS, and 31P CP MAS NMR spectroscopy on synthetic material. For phosphoellenbergerite, the two proton sites, Hl and H2, detected in single-crystal XRD studies, are confirmed. The protons on the first site, Hl, delocalized around the threefold axis, form OH groups with the unshared apical O atom of P[O.sub.4] tetrahedra. Those on the second site, H2, belong to [Mg.sub.2][O.sub.8]OH dimers of face-sharing Mg octahedra, which form double chains. The spectroscopic data reveal additional protons (H3) in phosphoellenbergerite. By combining both crystallographic and spectroscopic data, it can be inferred that the H3 protons are associated with Mg vacancies in the single chains of face-sharing Mg octahedra. Furthermore, a quantitative inspection of signal intensities indicates that the proton sites in synthetic phosphoellenbergerite are not all saturated. Therefore, the substitution [P.sup.5+] = [Si.sup.4+] + [H.sup.+] might account for part of the Si-P replacement in the silicate-to-phosphate ellenbergerite series. The results obtained for the proton distribution in holtedahlite, [Mg.sub.2][PO.sub.4]OH, were used as a reference to facilitate the interpretation of the IR and NMR spectra of phosphoellenbergerite.

Basanitic glasses with known dissolved C concentrations have been analyzed using infrared spectroscopy to calibrate the molar absorptivity of carbonate. C is dissolved as carbonate complexes-in the glass resulting in absorption bands at 1525 and 1425 [cm.sup.-1]. Molar absorptivities of 283 [+ or -] 8 L/(mol cm) were determined for both 1525 and 1425 [cm.sup.-1] absorption bands. An integrated molar absorptivity of 60000 [+ or -] 1700 L/(mol [cm.sup.2]) was determined using the integrated area under the doublet. These values are about 2025% lower than those determined for tholeiitic and leucititic glasses and are intermediate between values characteristic of Na- and Ca-rich silicate glasses. Carbonate molar absorptivities for a range of basaltic glass compositions correlate with the molar ratio of Na/(Na + Ca).

Near-infrared spectra of hydrous silicate melts are reported up to 10 kbar and 1000 [degrees]C. Measurements were performed using an externally heated diamond-anvil cell that allows precise control of pressure and temperature. In hydrous glasses, changes in [H.sub.2]O speciation occur below the glass-transformation temperature; however, the standard enthalpy of the speciation reaction [H.sub.2]O + 0 = 2OH is very different for the melt and glass phases. For a peraluminous sodium aluminosilicate glass containing 8.1 wt% total [H.sub.2]O, the temperature dependence of the [H.sub.2]O speciation equilibrium can be described by two equations: In K = -2.65 - 1.91 X [10.sup.2] K [T.sup.-1] (glass phase, [delta]H = 1.6 kJ/mol) and 1n K = 3.04 3.64 x [10.sup.3] K [T.sup.-1] (melt phase, [delta]H = 30.3 kJ/mol). The intersection of these two equilibrium curves defines a glass-transformation temperature of 335 [degrees]C. The near-infrared spectrum of a peraluminous sodium silicate melt with 30-40 wt% H2Q:at 10 kbar and 1000 [degrees]C shows the presence of both OH and [H.sub.2]O however, exceptionally strong speciation changes occur upon quenching. From visual observation, it appears that at 10 kbar and 1000 [degrees]C there is complete miscibility between this melt and water. Therefore, these data constitute the first infrared spectra of a phase beyond the critical point in a system of silicate melt and [H.sub.2]O.

[Fe.sup.3+]-[A1.sup.3+] substitution in the octahedral site of 14 natural garnet samples was investigated through measurement of complete single-crystal infrared (IR) reflectance spectra across the grossular-andradite [[Ca.sub.3]([A1.sub.x][Fe.sub.1-x]),[Si.sub.3][O.sub.12]] binary. Frequencies of all 17 IR-active fundamental modes depend nearly linearly on composition. Two peaks assigned to translations of the octahedral cations against the O framework exhibit two-mode behavior. Observation of similar frequencies for bands involving Al and Fe3+ and of much larger intensities for bands associated with [Fe.sup.3+] suggests that the Fe-O bond has greater strength, which compensates for the greater mass of Fe. The nearly linear behavior of the modes indicates that mixing should approach ideality for this series, as was previously observed in thermodynamic studies. The existence of ideal mixing suggests that high degrees of ordering are not present, and thus that ordering might not cause the anomalous birefringence associated with finis series.

Cation ordering of Fddd or the symmetric reductions of optically anomalous garnets from Ia3D to I1 reveals that most of the vibrations are active in the infrared regions. This factor is also indicated by crystallographic investigations. The infrared reflectance spectra within 80 to 4000 lines per centimeter revealed the characteristic pattern of the isotropic and isometric garnets. The spectra were sometimes polarized. The crystallographic refining revealed the samples to be similar. The complete fundamental region appears to be resolved in the first single crystal infrared absorption spectrum.

A study was conducted on the kinetics of the marcasite-pyrite solid-state transformation using infrared spectroscopy. The Arrhenius equation was used to determine the activation energy of the marcasite-to-pyrite conversion. A second-order Johnson-Mehl equation was used to model the transformation, proposing a growth and nucleation model for pyriteformation in the marcasite matrix. Kinetic analysis was also undertaken based on infrared absorption intensity data which used either the Johnson-Mehl or Avrami-Erofe'ev equation.

A study on the defect microstructure and oxidation state of iron in two olivine crystals from the Dish Hill cinder cone in California's Deadman Lake Volcanic Field was presented. The crystals were subjected to polarized infrared spectroscopy, transmission electron microscopy and Mossbauer spectroscopy to determine their composition. Results indicate that the crystals contained individual layers of laihunite.

The content of hydrous species in crystalline and metamict titanite (CaTiSi[O.sub.5]) have been investigated using polarized infrared spectroscopy. The effects of metamictization are a decrease of intensity and a broadening of Ti-O and Si-O stretching overtones, accompanied by development of the isotropic spectral features of hydrous species. Metamict and partially metamict titanites show OH contents up to 0.73 wt% [H.sub.2]O on the basis of previously reported calibrations. On heating, crystalline and metamict titanite showed a different temperature evolution of their OH content. Thermal annealing of crystalline titanite at temperatures above 1100 K for 15 min resulted in dehydration, characterized by a dramatic decrease in the intensity of the OH signal near 3486 [cm.sup.-1] in contrast to a two-stage dehydration process in metamict titanite. The results show that the high OH contents in metamict titanites are probably due to hydrogen diffusion during and after metamictzation. The results also show that the recrystallization in metamict titanite at high temperatures involves epitaxial growth of crystalline domains.

Vibrational spectra are used to determine key physical properties of phases thought to be important in Earth's transition zone. Single-crystal infrared (IR) reflectance spectra were measured for synthetic Mg, Fe, Ni, or Co-bearing silicates with the spinel structure. Peak parameters (frequency, damping coefficient, and oscillator strength) were determined for the fundamentals, and for overtones, up to 3rd order. On average, the frequencies and damping coefficients of the overtones are simple multiples of the corresponding parameters of the fundamental modes. Absorption spectra of thin films were measured at pressures (P) up to 370 kbar for [Gamma]-[Mg.sub.2][SiO.sub.4] and up to 200 kbar for [Gamma][Fe.sub.2][SiO.sub.4]. Widths are nearly constant, but frequencies ([v.sub.i] increase either linearly or quadratically with P. For weak peaks, the absorption widths have values close to their corresponding damping coefficients. For [Gamma]-[Fe.sub.2][SiO.sub.4], ambient IR data predict heat capacity ([C.sub.v] = 126 [+ or -] 2.5 J/mo1.K), shear modulus (G = 875 [+ or -] 15 kbar), and sound velocities (Up= 8.20 [+ or -] 0.05, [u.sub.s]= 4.25 [+ or -] 0.06 km/s) at 298 K; pressure data give [Delta]G/[Delta]P = 0.06, 0.44, or 0.91 if for the bulk modulus, [Delta]K/[Delta]P = 5, 4.5, or 4, respectively, and an average mode Gruneisen parameter of = 1.45 [+ or -] 0.4, which implies that thermal expansivity is (21 [+ or -] 1) x [10.sup.-6]/K. For [Gamma]-[Mgt.sub.1.2][Fe.sub.08][SiO.sub.4], ambient IR data predict G = 1120 [+ or -] 50 kbar, [u.sub.p]= 9.12 [+ or -] 0.20, and [u.sub.s]= 5.18 [+ or -] 0.20 km/s at 298 K, assuming that the frequency of the acoustic mode is 225 to 240 [cm.sup.-1]. This calculation uses [K.sub.s] = 1995 kbar, which was obtained from recent compression data by assuming [Delta]K/[Delta]P = 4. The above values provide a smooth quadratic dependence of Ks and G on Fe/(Fe + Mg). The trends suggest that [Delta]K/[Delta]P remains at 4 whereas [Delta]G/[Delta]P drops from [similar to] 1 to [similar to] 0.5 as Fe content increases in ringwoodite. Acoustic fundamentals or overtones were used successfully here to provide u, G, and their P and T derivatives for silicate spinels. This method should work for other simple structures, and may be generally applicable.

The crystal structures of six birefringent uvarovite-grossular garnets from three localities (Saranov, Veselovsk, and Saranka, Ural Mountains, Russia) were investigated using single-crystal X-ray CCD diffraction data. The intensity and lattice parameter data attest to the violation of the cubic garnet space group Ia[bar]3d and the symmetry reduction to subgroups with triclinic (I[bar]1), monoclinic (I2/a), or at most orthorhombic symmetry (Fddd). Careful structure refinements starting in space group I[bar]1 reveal that partial long-range C[r.sup.3+]/Al ordering on the octahedral sites is the most prominent noncubic feature. For each crystal, a nearly perfect linear correlation of the individual octahedral size with its Cr occupancy is observed. Considering the dependence on the bulk Cr mole fraction, the individual octahedral size in non-cubic uvarovite-grossular solid solutions is represented by < Cr/AlO > ([Angstrom]) = 1.9247 + 0.0147 [X.sub.Cr(bulk)] + 0.0534 [X.sub.Cr(individual)]. These uvarovites also structurally incorporate traces of hydrous component (< 1 wt% [H.sub.2]O) as [O.sub.4][H.sub.4] 'hydrogarnet' substitution in a non-cubic way, thus leading to further subtle deviations from cubic symmetry. Within the range of these low water contents, the refined Si-O bond length, averaged over crystallographically different tetrahedra, correlates with the total integral OH absorption coefficient [[alpha].sub.i] through the equation <> ([Angstrom]) = 1.6455 + 1.0074 * [10.sup.-7][alpha] [sub.i]([cm.sup.-2]). Although the Si and Ca atoms occupy general positions in I[bar]1, they deviate little from their respective special positions in Ia[bar]3d. Consistent with the respective angular lattice distortions, the refined [Cr.sup.3+]/Al site distribution pattern is definitely triclinic in the Saranka sample, somewhat less pronounced triclinic (pseudomonoclinic) in the Veselovsk sample, and distinctively pseudo-orthorhombic or orthorhombic in all four samples from the Saranov locality. Considering crystal chemical evidence, three of the pseudo-orthorhombic Saranov samples with elevated water content appear to have triclinic symmetry as well, while one low-water uvarovite is classified as orthorhombic. These results are in good agreement with those of optical and UV-VIS-IR spectroscopic investigations reported in Part I of the present study (Andrut and Wildner 2001). Previous structure data for birefringent garnets reported in the literature as non-cubic are compared and discussed. Special emphasis is also drawn to structural and crystal chemical details exhibiting a non-ideal mixing behavior along the uvarovite-grossular join. Evidence for and against the cation ordering models postulated in the literature are discussed.

Six garnet crystals with compositions close to the uvarovite-grossular binary from three different localities (Saranov, Veselovsk, and Saranka, Ural Mountains, Russia) were investigated by optical methods, electron microprobe analysis, and polarized UV-VIS-IR micro-spectroscopy. Under crossed polarizers the crystals display 'strong' birefringence in the order of 0.006 and formation of domains, aligned parallel to the crystal faces of the form {110}. Referring to the cubic cell, Y is always parallel to a principal lattice direction, e.g., [[010].sub.cub], whereas X and Z are then parallel to [[101].sub.cub] and [[10[bar]1].sub.cub], respectively. The garnets are uvarovite-grossular solid solutions with 48 to 71 mol% uvarovite component and traces of Ti, Fe, Mn, and Mg, and exhibit no compositional zoning. Polarized single crystal infrared absorption spectra in the region of the OH stretching vibration display 14 discernible, partly superimposing, and strongly anisotropic absorption bands between 3470 and 3680 c[m.sup.-1], which are caused by structurally incorporated hydroxyl groups. The polarization behavior observed for individual samples complies with orthorhombic, monoclinic, and triclinic crystal symmetry, respectively. The water content calculated using an integral extinction coefficient, [epsilon] = 43800 L/c[m.sup.2] * mol, ranges from 0.07 to 0.34 wt%. Annealing experiments indicate that the incorporation of hydroxyl groups is not the primary cause for the anisotropic behavior. Instead, cation ordering on octahedral positions may play an important role. This assumption is substantiated by single crystal X-ray diffraction investigations reported in Part II of the present study (Wildner and Andrut 2001). Contrary to the IR spectroscopic data, single-crystal electronic absorption spectra show no significant polarization behavior in the UV-VIS-NIR spectral region. The observed absorption bands are caused by d-d transitions of C[r.sup.3+] cations in octahedral coordination. The linear extinction coefficients of the investigated uvarovites strongly indicate that the C[r.sup.3+] cations occupy centrosymmetric sites, regardless of the exact symmetry reduction from Ia[bar]3d.