Raman spectroscopy of uranyl rare earth carbonate kamotoite-(Y)

Raman spectroscopy at 298 and 77K has been used to study the mineral kamotoite-(Y), a uranyl rare earth carbonate mineral of formula Y(2)(UO(2))(4)(CO(3))(3)(OH)(8).10-11H(2)O. The mineral is characterised by two Raman bands at 1130.9 and 1124.6 cm(-1) assigned to the nu(1) symmetric stretching mode of the (CO(3))(2-) units, while those at 1170.4 and 862.3 cm(-1) (77K) to the deltaU-OH bending vibrations. The assignment of the two bands at 814.7 and 809.6 cm(-1) is difficult because of the potential overlap between the symmetric stretching modes of the (UO(2))(2+) units and the nu(2) bending modes of the (CO(3))(2-) units. Only a single band is observed in the 77K spectrum at 811.6 cm(-1). One possible assignment is that the band at 814.7 cm(-1) is attributable to the nu(1) symmetric stretching mode of the (UO(2))(2+) units and the second band at 809.6 cm(-1) is due to the nu(2) bending modes of the (CO(3))(2-) units. Bands observed at 584 and 547.3 cm(-1) are attributed to water librational modes. An intense band at 417.7 cm(-1) resolved into two components at 422.0 and 416.6 cm(-1) in the 77K spectrum is assigned to an Y(2)O(2) stretching vibration. Bands at 336.3, 286.4 and 231.6 cm(-1) are assigned to the nu(2) (UO(2))(2+) bending modes. U-O bond lengths in uranyl are calculated from the wavenumbers of the uranyl symmetric stretching vibrations. The presence of symmetrically distinct uranyl and carbonate units in the crystal structure of kamotoite-(Y) is assumed. Hydrogen-bonding network related to the presence of water molecules and hydroxyls is shortly discussed.     

Raman microscopy of autunite minerals at liquid nitrogen temperature

Uranyl micas are based upon (UO(2)PO(4))(-) units in layered structures with hydrated counter cations between the interlayers. Uranyl micas also known as the autunite minerals are of general formula M(UO2)2(XO4)2 x 8-12H2O where M may be Ba, Ca, Cu, Fe(2+), Mg, Mn(2+) or 1/2(HA1) and X is As or P. The structures of these minerals have been studied using Raman microscopy at 298 and 77K. Six hydroxyl stretching bands are observed of which three are highly polarised. The hydroxyl stretching vibrations are related to the strength of hydrogen bonding of the water OH units. Bands in the Raman spectrum of autunite at 998, 842 and 820 cm(-1) are highly polarised. Low intensity band at 915 cm(-1) is attributed to the nu(3) antisymmetric stretching vibration of (UO(2))(2+) units. The band at 820 cm(-1) is attributed to the nu(1) symmetric stretching mode of the (UO(2))(2+) units. The (UO(2))(2+) bending modes are found at 295 and 222 m(-1). The presence of phosphate and arsenate anions and their isomorphic substitution are readily determined by Raman spectroscopy. The collection of Raman spectra at 77K enables excellent band separation.     

A Raman spectroscopic study of the uranyl phosphate mineral bergenite

Raman spectroscopy at 298 and 77 K of bergenite has been used to characterise this uranyl phosphate mineral. Bands at 995, 971 and 961 cm-1 (298 K) and 1006, 996, 971, 960 and 948 cm-1 (77K) are assigned to the nu1(PO4)3- symmetric stretching vibration. Three bands at 1059, 1107 and 1152 cm-1 (298 K) and 1061, 1114 and 1164 cm-1 (77 K) are attributed to the nu3(PO4)3- antisymmetric stretching vibrations. Two bands at 810 and 798 cm-1 (298 K) and 812 and 800 cm-1 (77 K) are attributed to the nu1 symmetric stretching vibration of the (UO2)2+ units. Bands at 860 cm-1 (298 K) and 866 cm-1 (77 K) are assigned to the nu3 antisymmetric stretching vibrations of the (UO2)2+ units. UO bond lengths in uranyls, calculated using the wavenumbers of the nu1 and nu3(UO2)2+ vibrations with empirical relations by Bartlett and Cooney, are in agreement with the X-ray single crystal structure data. Bands at (444, 432, 408 cm-1) (298 K), and (446, 434, 410 and 393 cm-1) (77 K) are assigned to the split doubly degenerate nu2(PO4)3- in-plane bending vibrations. The band at 547 cm-1 (298 K) and 549 cm-1 (77 K) are attributed to the nu4(PO4)3- out-of-plane bending vibrations. Raman bands at 3607, 3459, 3295 and 2944 cm-1 are attributed to water stretching vibrations and enable the calculation of hydrogen bond distances of >3.2, 2.847, 2.740 and 2.637 A. These bands prove the presence of structurally nonequivalent hydrogen bonded water molecules in the structure of bergenite.     

A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite: part 2

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm(-1) region and in the 950-1000 cm(-1) region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. Soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm(-1), 909.6 and 898.0 cm(-1), and 268.2, 257.8 and 246.9 cm(-1), attributed to the nu1, nu3, and nu2 (delta) (UO2)2+, respectively. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm(-1) are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm(-1) region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm(-1) and in the 390-420 cm(-1) region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 and 3600-3700 cm(-1).     

A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals, including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm-1 region and in the 950-1000 cm-1 region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example, soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm-1 (UO2)2+ (nu1), 909.6 and 898.0 cm-1 (UO2)2+ (nu3), 268.2, 257.8 and 246.9 cm-1 are assigned to the nu2 (delta) (UO2)2+. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm-1 are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm-1 region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm-1 and in the 390-420 cm-1 region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 cm-1 and 3600-3700 cm-1.     

Raman spectroscopic study of the molecular structure of the uranyl mineral zippeite from Jáchymov (Joachimsthal), Czech Republic

Raman spectra at 298 and 77K and infrared spectra of the uranyl sulfate mineral zippeite from Jáchymov (Joachimsthal), Czech Republic, K(0.6)(H(3)O)0.4[(UO(2))6(SO(4))3(OH)7].8H2O, were studied. Observed bands were tentatively attributed to the (UO(2))2+ and (SO(4))2- stretching and bending vibrations, the OH stretching vibrations of water molecules, hydroxyls and oxonium ions, and H(2)O, oxonium, and delta U-OH bending vibrations. Empirical relations were used for the calculation of U-O bond lengths in uranyl R (A)=f(nu(3) or nu(1)(UO(2))2+). Calculated U-O bond lengths are in agreement with U-O bond lengths from the single crystal structure analysis and those inferred for uranyl anion sheet topology of uranyl pentagonal dipyramidal coordination polyhedra. The number of observed bands supports the conclusion from single crystal structure analysis that at least two symmetrically distinct U6+ (in uranyls) and S6+ (in sulfates), water molecules and hydroxyls may be present in the crystal structure of the zippeite studied. Strong to very weak hydrogen bonds present in the crystal structure of zippeite studied were inferred from the IR spectra.     

Raman spectroscopy of likasite at 298 and 77 K

Raman spectroscopy at 298 and 77K has been used to study the structure of likasite, a naturally occurring basic copper(II) nitrate of formula Cu3NO3(OH)5.2H2O. An intense sharp band is observed at 3522 cm(-1) at 298 K which splits into two bands at 3522 and 3505 cm(-1) at 77 K and is assigned to the OH stretching mode. The two OH stretching bands at 3522 and 3505 provide estimates of the hydrogen bond distances of these units as 2.9315 and 2.9028 angstroms. The significance of this result is that equivalent OH units in the 298 K spectrum become two non-equivalent OH units at 77 K suggesting a structural change by cooling to liquid nitrogen temperature. A number of broad bands are observed in the 298 K spectrum at 3452, 3338, 3281 and 3040 cm(-1) assigned to H2O stretching vibrations with estimates of the hydrogen bond distances of 2.8231, 2.7639, 2.7358 and 2.6436 angstroms. Three sharp bands are observed at 77 K at 1052, 1050 and 1048 cm(-1) attributed to the nu1 symmetric stretching mode of the NO3 units. Only a single band at 1050 cm(-1) is observed at 298 K, suggesting the non-equivalence of the NO3 units at 77 K, confirming structural changes in likasite by cooling to 77 K.     

Peisleyite an unusual mixed anion mineral--a vibrational spectroscopic study

The mineral peisleyite has been studied using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscope (SEM) photomicrographs reveal that the peisleyite morphology consists of an array of small needle-like crystals of around 1 microm in length with a thickness of less than 0.1 microm. Raman spectroscopy in the hydroxyl stretching region shows an intense band at 3506 cm(-1) assigned to the symmetric stretching mode of the OH units. Four bands are observed at 3564, 3404, 3250 and 3135 cm(-1) in the infrared spectrum. These wavenumbers enable an estimation of the hydrogen bond distances 3.052(5), 2.801(0), 2.705(6) and 2.683(6)A. Two intense Raman bands are observed at 1023 and 989 cm(-1) and are assigned to the SO(4) and PO(4) symmetric stretching modes. Other bands are observed at 1356, 1252, 1235, 1152, 1128, 1098 and 1067 cm(-1). The bands at 1067 cm(-1) is attributed to AlOH deformation vibrations. Bands in the low wavenumber region are assigned to the nu(4) and nu(2) out of plane bending modes of the SO(4) and PO(4) units. Raman spectroscopy is a useful tool in determining the vibrational spectroscopy of mixed hydrated multianion minerals such as peisleyite. Information on such a mineral would be difficult to obtain by other means.     

A Raman spectroscopic study of synthetic giniite

The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive-green giniite display a very unusual image of pseudo-spheres with roughened surfaces of around 1-10microm in size. The face to face contact of the spheres suggests that the spheres are colloidal and carry a surface charge. Raman spectroscopy proves the (PO4)3- units are reduced in symmetry and in all probability more than one type of phosphate unit is found in the structure. Raman bands at 77K are observed at 3380 and 3186cm-1 with an additional sharp band at 3100cm-1. The first two bands are assigned to water stretching vibrations and the latter to an OH stretching band. Intense Raman bands observed at 396, 346 and 234cm-1are attributed to the FeO stretching vibrations. The giniite phosphate units are characterised by two Raman bands at 1023 and 948cm-1 assigned to symmetric stretching mode of the (PO4)3- units. A complex band is observed at 460.5cm-1 with additional components at 486.8 and 445.7cm-1 attributed to the nu(2) bending modes suggesting a reduction of symmetry of the (PO4)3- units.     

Raman spectroscopic study of the tellurite minerals: rajite and denningite

Tellurites may be subdivided according to formula and structure. There are five groups based upon the formulae (a) A(XO3), (b) A(XO3).xH2O, (c) A2(XO3)3.xH2O, (d) A2(X2O5) and (e) A(X3O8). Raman spectroscopy has been used to study rajite and denningite, examples of group (d). Minerals of the tellurite group are porous zeolite-like materials. Raman bands for rajite observed at 740, and 676 and 667 cm(-1) are attributed to the nu1 (Te2O5)(2-) symmetric stretching mode and the nu3 (TeO3)(2-) antisymmetric stretching modes, respectively. A second rajite mineral sample provided a more complex Raman spectrum with Raman bands at 754 and 731 cm(-1) assigned to the nu1 (Te2O5)(2-) symmetric stretching modes and two bands at 652 and 603 cm(-1) are accounted for by the nu3 (Te2O5)(2-) antisymmetric stretching mode. The Raman spectrum of dennigite displays an intense band at 734 cm(-1) attributed to the nu1 (Te2O5)(2-) symmetric stretching mode with a second Raman band at 674 cm(-1) assigned to the nu3 (Te2O5)(2-) antisymmetric stretching mode. Raman bands for rajite, observed at (346, 370) and 438 cm(-1) are assigned to the (Te2O5)(2-)nu2 (A1) bending mode and nu4 (E) bending modes.     

A Raman spectroscopic study of the uranyl phosphate mineral threadgoldite

Raman spectra of threadgoldite at 298 and 77K are measured and interpreted for the first time. Bands related the (UO(2))(2+) and (PO(4))(3-) stretching and bending vibrations are tenatively attributed together with the bands assigned to the stretching a and bending vibrations of water molecules and hydroxyls. Hydrogen-bonding network and H(2)O and (OH)(-1) libration modes are mentioned. U-O bond lengths in uranyls are calculated via empirical relations R(U-O)=f[nu(1) and nu(3)(UO(2))(2+)]A. They are comparable to the values inferred from the single crystal structure analysis of threadgoldite.     

Raman and infrared spectroscopy of the manganese arsenate mineral allactite

The mineral allactite [Mn(7)(AsO(4))(2)(OH)(8)] is a basic manganese arsenate which is highly pleochroic. The use of the 633 nm excitation line enables quality spectra of to be obtained irrespective of the crystal orientation. The mineral is characterised by a set of sharp bands in the 770-885 cm(-1) region. Intense and sharp Raman bands are observed at 883, 858, 834, 827, 808 and 779 cm(-1). Collecting the spectral data at 77K enabled better band separation with narrower bandwidths. The observation of multiple AsO(4) stretching bands indicates the non-equivalence of the arsenate anions in the allactite structure. In comparison the infrared spectrum shows a broad spectral profile with a series of difficult to define overlapping bands. The low wavenumber region sets of bands which are assigned to the nu(2) modes (361 and 359 cm(-1)), the nu(4) modes (471, 452 and 422 cm(-1)), AsO stretching vibrations at 331 and 324 cm(-1), and bands at 289 and 271 cm(-1) which may be ascribed to MnO stretching modes. The observation of multiple bands shows the loss of symmetry of the AsO(4) units and the non-equivalence of these units in the allactite structure. The study shows that highly pleochroic minerals can be studied by Raman spectroscopy.     

Raman spectroscopic determination of equilibrium constants of uranyl sulphate complexes in aqueous solutions

Raman spectra are used to determine the formation constants of uranyl sulphate complexes in aqueous solutions at 20 degrees and remedy the confusion existing in this area in the available literature. Solutions with a varying total sulphate concentration and an ionic strength lower than 0.4M are analysed. The species UO(2)SO(4) and UO(2)(SO(4))(2-)(2) are characterized by a resolved Raman band at 861 cm(-1) and an unresolved one at 852 cm(-1), corresponding to the uranyl symmetrical stretching vibration. The equilibrium constants, in term of activity (standard state 1M), are found to be about 1400 and 11, respectively, for the consecutive reactions: UO(2+)(2)(aq)+SO(2-)(4)(aq)=UO(2)SO(4)(aq) and UO(2)SO(4)(aq)+SO(2-)(4)(aq)=UO(2)(SO(4))(2-)(2)(aq).     

An infrared and Raman spectroscopic study of the uranyl micas

Vibrational spectroscopy using a combination of infrared and Raman spectroscopy has been used to study the uranyl micas also known as the autunite minerals, of general formula M(UO2)2(XO4)2.8-12H2O where M may be Ba, Ca, Cu, Fe2+, Mg, Mn2+ or 1/2(HAl) and X is As or P. Included in these minerals are autunite, metautunite, torbernite, meta-torbernite, meta-zeunerite, saléeite and sabugalite. Compared with the results of infrared spectroscopy, Raman microscopy shows excellent band separation enabling the separation and identification of bands attributed to (UO2)2+ units, PO4 and AsO4 units. Common to all spectra were bands at around 900 and 818 cm(-1), attributed to the antisymmetric and symmetric stretching vibrations of the (UO2)2+ units. Water in autunites is in a highly structured arrangement in the interlayer of the uranyl micas. Water molecules are differentiated according to the strength of the hydrogen bonds formed between the water and the adjacent uranyl-phosphate or uranyl-arsenate surfaces and the hydration sphere of the interlayer cation.     

Raman spectroscopy of the mineral rhodonite

The mineral rhodonite an orthosilicate has been characterised by Raman spectroscopy. The Raman spectra of three rhodonites from Broken Hill, Pachapaqui and Franklin were compared and found to be similar. The spectra are characterised by an intense band at around 1000 cm(-1) assigned to the nu(1) symmetric stretching mode and three bands at 989, 974 and 936 cm(-1) assigned to the nu(3) antisymmetric stretching modes of the SiO(4) units. An intense band at around 667 cm(-1) was assigned to the nu(4) bending mode and showed additional bands exhibiting loss of degeneracy of the SiO(4) units. The low wave number region of rhodonite is complex. A strong band at 421.9 cm(-1) is attributed to the nu(2) bending mode. The spectra of the three rhodonite mineral samples are similar but subtle differences are observed. It is proposed that these differences depend upon the cationic substitution of Mn by Ca and/or Fe(2+) and Mg.     

Raman spectroscopic study of the tellurite minerals: carlfriesite and spiroffite

Raman spectroscopy has been used to study the tellurite minerals spiroffite and carlfriesite, which are minerals of formula type A(2)(X(3)O(8)) where A is Ca(2+) for the mineral carlfriesite and is Zn(2+) and Mn(2+) for the mineral spiroffite. Raman bands for spiroffite observed at 721 and 743 cm(-1), and 650 cm(-1) are attributed to the nu(1) (Te(3)O(8))(2-) symmetric stretching mode and the nu(3) (Te(3)O(8))(2-) antisymmetric stretching modes, respectively. A second spiroffite mineral sample provided a Raman spectrum with bands at 727 cm(-1) assigned to the nu(1) (Te(3)O(8))(2-) symmetric stretching modes and the band at 640cm(-1) accounted for by the nu(3) (Te(3)O(8))(2-) antisymmetric stretching mode. The Raman spectrum of carlfriesite showed an intense band at 721 cm(-1). Raman bands for spiroffite, observed at (346, 394) and 466 cm(-1) are assigned to the (Te(3)O(8))(2-)nu(2) (A(1)) bending mode and nu(4) (E) bending modes. The Raman spectroscopy of the minerals carlfriesite and spiroffite are difficult because of the presence of impurities and other diagenetically related tellurite minerals.     

ThermoRaman spectroscopic study of kintoreite

ThermoRaman spectroscopy has been used to study the molecular structure and thermal decomposition of kintoreite, a phosphated jarosite PbFe3(PO4)2(OH,H2O)6. Infrared spectroscopy shows the presence of significant amounts of water in the structure as well as hydroxyl units. In contrast, no water was observed for segnitite (the arsenojarosite) as determined by infrared spectroscopy. The Raman spectra at 77 K exhibit bands at 974.6, 1003.2 and 866.5 cm(-1). These bands are attributed to the symmetric stretching vibrations of (PO4)3-, (SO4)3- and (AsO4)3- units. Raman spectroscopy confirms the presence of both arsenate and phosphate in the structure. Bands at 583.7 and 558.1 cm(-1) in the 77 K spectrum are assigned to the nu4 (PO4)3- bending modes. ThermoRaman spectroscopy of kintoreite identifies the temperature range of dehydration and dehydroxylation.     

Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440cm(-1) is assigned to the nu(3) CO(3)(2-) antisymmetric stretching vibration. An additional band is resolved at 1335cm(-1). An intense sharp Raman band at 1092cm(-1) is assigned to the CO(3)(2-) symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442cm(-1) shifting to lower wavenumbers with thermal treatment. A band observed at 870cm(-1) with a band of lesser intensity at 842cm(-1) shifts to higher wavenumbers upon thermal treatment and is observed at 865cm(-1) at 400 degrees C and is assigned to the CO(3)(2-)nu(2) mode. No nu(2) bending modes are observed in the Raman spectra for smithsonite. The band at 746cm(-1) shifts to 743cm(-1) at 400 degrees C and is attributed to the CO(3)(2-)nu(4) in phase bending modes. Two infrared bands at 744 and around 729cm(-1) are assigned to the nu(4) in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO(6) octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991cm(-1) in both the IE and infrared spectra are attributed to combination bands.     

Raman spectroscopy of halotrichite from Jaroso, Spain

Raman spectroscopy complimented with infrared ATR spectroscopy has been used to characterise a halotrichite FeSO(4) x Al(2)(SO(4))(3) x 22 H(2)O from The Jaroso Ravine, Aquilas, Spain. Halotrichites form a continuous solid solution series with pickingerite and chemical analysis shows that the jarosite contains 6% Mg(2+). Halotrichite is characterised by four infrared bands at 3569.5, 3485.7, 3371.4 and 3239.0 cm(-1). Using Libowitsky type relationships, hydrogen bond distances of 3.08, 2.876, 2.780 and 2.718 Angstrom were determined. Two intense Raman bands are observed at 987.7 and 984.4 cm(-1) and are assigned to the nu(1) symmetric stretching vibrations of the sulphate bonded to the Fe(2+) and the water units in the structure. Three sulphate bands are observed at 77K at 1000.0, 991.3 and 985.0 cm(-1) suggesting further differentiation of the sulphate units. Raman spectrum of the nu(2) and nu(4) region of halotrichite at 298 K shows two bands at 445.1 and 466.9 cm(-1), and 624.2 and 605.5 cm(-1), respectively, confirming the reduction of symmetry of the sulphate in halotrichite.     

Vibrational spectroscopy of stichtite

Raman spectroscopy complimented with infrared spectroscopy has been used to study the mineral stitchtite, a hydrotalcite of formula Mg6Cr2(CO3)(OH)16.4H2O. Two bands are observed at 1087 and 1067 cm(-1) with an intensity ratio of approximately 2.5/1 and are attributed to the symmetric stretching vibrations of the carbonate anion. The observation of two bands is attributed to two species of carbonate in the interlayer, namely weakly hydrogen bonded and strongly hydrogen bonded. Two infrared bands are found at 1457 and 1381 cm(-1) and are assigned to the antisymmetric stretching modes. These bands were not observed in the Raman spectrum. Two infrared bands are observed at 744 and 685 cm(-1) and are assigned to the nu4 bending modes. Two Raman bands were observed at 539 and 531 cm(-1) attributed to the nu2 bending modes. Importantly the band positions of the paragenically related hydrotalcites stitchtite, iowaite, pyroaurite and reevesite all of which contain the carbonate anion occur at different wavenumbers. Consequently, Raman spectroscopy can be used to distinguish these minerals, particularly in the field where many of these hydrotalcites occur simultaneously in ore zones.