Mineralogical Magazine, December 2002, Vol. 66(6), pp. 1063–1073

Raman andinfrared spectroscopicstudyof the vivianite-groupphosphates vivianite,bar iciteandbobierrite

1, 1 2 1 R. L. FROST *, W. MARTENS , P. A. WILLIAMS AND J. T. KLOPROGGE 1 Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, GPOBox 2434, Brisbane Queensland 4001, Australia 2 School of Science, Food and Horticulture, University of Western Sydney, Locked Bag 1797, Penrith South DC NSW1797, Australia

ABSTRACT

Themolecular structure of the three vivianite-structure ,compositionallyrelated phosphate minerals 2+ vivianite,baricite and bobierrite of formula M3 (PO4)2.8H2O where M isFe orMg, has been assessed usinga combinationof Raman and infrared (IR) spectroscopy. The Raman spectra of the hydroxyl- stretchingregion are complex with overlapping broad bands. Hydroxyl stretching vibrations are identifiedat 3460,3281, 3104 and 3012 cm ­ 1 forvivianite. The high wavenumber band is attributedto thepresence of FeOH groups.This complexity is reflected in the water HOH-bending modes where a strongIR bandcentred around 1660 cm ­ 1 isfound. Such a bandreflects the strong hydrogen bonding ofthe water molecules to the phosphate anions in adjacent layers. Spectra show three distinct OH- bendingbands from strongly hydrogen-bonded, weakly hydrogen bonded water and non-hydrogen bondedwater. The Raman phosphate PO-stretching region shows strong similarity between the three minerals.In the IR spectra,complexity exists with multiple antisymmetric stretching vibrations observed,due to the reduced tetrahedral symmetry. This loss of degeneracy is also reflected in the bendingmodes. Strong IR bandsaround 800 cm ­ 1 areattributed to water librational modes. The spectraof the three minerals display similarities due to their compositions and crystal structures, but sufficientsubtle differences exist for the spectra to be useful in distinguishing the species.

KEY WORDS: baricite,bobierrite, vivianite, iron, phosphate, Raman spectroscopy, infrared spectroscopy.

Introduction morassesand sediments (Henderson et al., 1984). 2+ 2+ THE vivianitegroup of mineralsare of thegeneral Ifgroundwaters are high in both Mg and Fe 2+ 2+ formula A3 (XO4)2·8H2O where A may be Co, thenit is possible that both the minerals of the Fe,Mg, Ni, Zn and X isAs or P. Vivianiteand vivianitegroup such as baricite and bobierrite bariciteare the Fe- and Mg-dominant phosphates mayform, particularly when phosphate fertilizers inthe group, respectively. Baricite possesses a havebeen used in the surrounding farmlands. In morecommon diamorph, bobierri te,with a fact,these minerals have been found in sediments doubledunit-cell volume. Extensive solid solution inNew Zealand(Anthony et al., 2000). The formationoccurs between baricite and vivianite. vivianiteminerals are all monoclinic and belong Isomorphoussubstitution in this group occurs topoint group 2/ m (Anthony et al., 2000). The readilyand intermediate compositions are often mineralsmay be divide dintotwo groups observed.The minerals are of interestbecause of accordingto the oxyanion being either arsenate theiroccurrence in environments such as the orphosphate (Wolfe 1940). The phosphates in 2+ coatingsof waterpipes and soils from peat bogs, thismineral group are arupite (Ni 3 (PO4)2·8H2O), 2+ 2+ vivianite(Fe 3 (PO4)2·8H2O),baricite((Mg,Fe )3 2+ (PO4)2·8H2O)andbobierrite (Mg 3 (PO4)2·8H2O). *E-mail: [email protected] SomeIR dataexist for the vivianite-group DOI: 10.1180/0026461026660077 phosphateand arsenate minerals (Farmer, 1974).

# 2002The Mineralogical Society R. L. FROSTETAL.

However,most IR datapredate the advent of stretchingmode was not listed but the antisym- Fouriertransform IR spectroscopy(Gevork’ yan metricmode was found at 990 and 1040 cm ­ 1. andPovarennykh, 1973, 1980; Hunt 1977; Hunt et Bandsat 890and 872 cm ­ 1 werenot assigned. It al., 1972;Omori and Seki, 1960; Sitzia, 1966). isprobablethat these are the symmetric stretching Althoughsome Raman studies of the vivianite modesof thehydrogen-bonded phosphate. Bands phosphatemineralsha veb eenu ndertaken for the n4 modewere observed at 475, 560 and (Melendres et al., 1989;Piriou and Poullen, 590 cm ­ 1.Theformula is close to that of 1984),no Raman spectroscopic investigation of bobierrite.GrifŽ th (1970) reported the Raman thesephosphate phase-related minerals has been spectraof vivianite. forthcoming.The Raman spectra of the tetra- Ourinterest in theseminerals arose because of hedralanions in aqueous systems are well known. theobservation of some blue materials found in Thesymmet ricstretc hingvib rationof the someacid drainage soils in both the Shoalhaven phosphateanion in aqueous systems ( n1) is Plateauin NSW, Australiaand in some soil observedat 938 cm ­ 1,theasymmetric stretching drainagematerials in South Australia. There is ­ 1 mode (n3) at 1018 cm . The n2 mode is currentlya lackof comprehensivespectral knowl- ­ 1 observedat 420 cm and the n4 mode at edgeof the vivianite phosphate minerals and as 567 cm ­ 1.Insolids, the position of the bands partof a widercomprehensive study of the willbe dependent on the chemical environment. vibrationalspectroscopy of secondary minerals, Farmer(1974) lists a numberof IR spectraof wereport the molecular structure of the phosphate phosphatesincluding vivianite. The symmetric mineralsof the vivianite group.

FIG.1. Raman spectra of the hydroxyl-stretching region of ( a)vivianite, ( b)baricite and ( c)bobierrite.

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Experimental USA). Band-componentanalysis was undertaken Minerals usingthe Jandel ‘ PeakŽt’ software package, whichenabled the type of Ž ttingfunction to be Thevivianite was obtained from BK minerals selectedand allowsspeciŽ c parametersto be Ž xed (Brisbane,Queensland, Australia) and was in the orvariedaccordingly. Band Ž ttingwas done using formof large, deep blue, prismatic crystals. The aGauss-Lorentzcross-product function with the mineraloriginated from the Ukraine. The baricite minimumnumber of component bands used to waslent to us by the South Australian museum, achievea satisfactoryŽ t.The Gauss-Lorentz ratio registeredsamplenumber SAM 15065,and wasmaintained at values greater than 0.7 and originatedfrom Big Fish River/ Rapidcreek, Žttingwas undertaken until reproducible results RichardsonMounta ins,Yuko n,Ca nada.A wereobtaine dwithsquared correla tionsof sampleof baricite was also obtaine dfrom r2 >0.995. sedimentinaraisedbeach,Marlborough Province,New Zealand.The bobierrite came fromthe Zhelezn yiMine, Kovdor deposit , Results anddiscuss ion KovdorMassif,Kolapeninsula,Russia. Hydroxyl-stretchingregion Bobierriteswere also obtained from Wodinga, TheRaman and IR spectraof vivianite, baricite Pilbara,WesternAustraliaandfrom andbobierri teare shown in Figs 1 and2 Marlborough,New Zealand. respectively.The analysis of the Raman and IR spectraare reported in Table 1. Vivianite shows well-resolvedbands in the hydroxyl-stretching Ramanm icroprobespectros copy regionat3496,3482,3262,3130and Thecrystals of thevivianite minerals were placed 3012 cm­ 1.Thebands are broad with bandwidths andoriented on a polishedmetal surface on the >200 cm ­ 1.Previousstudies have not reported the stageof anOlympusBHSM microscope,which is Ramanspectra of the hydroxyl-stretching region equippedwith 10 6 and 506 objectives.The (GrifŽth, 1970; Piriou and Poullen, 1984). In the IR microscopeis part of a Renishaw1000 Raman spectraof vivianite, three distinct hydroxyl- microscopesystem, which also includ esa stretchingbands are observed at 3460, 3281 and monochromator,a Žltersystem and a Charge 3104 cm­ 1.Previousstudy gave bands at 3475, CoupledDevice (CCD). Ramanspectra were 3260and 3125 cm ­ 1,whichare in reasonable excitedby a Spectra-Physicsmodel 127 He-Ne agreementwith this work, considering the breadth laser(633 nm) at a resolutionof 2 cm ­ 1 in the ofthe bands in the hydroxyl-stretching region rangebetween 100 and 4000 cm ­ 1. Repeated (Piriouand Poullen, 1987). The band at 3262 cm ­ 1 acquisitionsusing the highest magniŽ cation were ismost intense in the Raman spectrum and is accumulatedto improve the signal to noise ratio assignedto the water OH symmetricstretching inthe spectra. Spectra were calibrated using the modewhilst the bands at 3460 and 3104 cm ­ 1 are 520.5 cm ­ 1 lineof a siliconwafer. Spectra at moreintense in theIR spectraand are attributed to liquidnitrogen temperature were obtained using a thewater OH-antisymmetric stretching modes. Linkamthermal stage (ScientiŽ c InstrumentsLtd, TheRaman spectra of both baricite and WaterŽeld, Surrey, England). bobierriteare less well resolved than that of vivianite,although the spectral proŽ les are similar (Fig.1). In the Raman spectrum of baricite,bands Infraredspectrosco py wereŽ ttedat 3480, 3300, 3231, 3121 and Infraredspectra were obtained using a Nicolet 3025 cm ­ 1.Correspondingly,bands were found Nexus870 FTIR spectrometerwith a smart inthe IR spectrumat 3498, 3373, 3168 and endurancesingle bounce diamond ATR cell. 2927 cm ­ 1.TheRamanspectrumo fthe Spectraover the 4000 to 525 cm ­ 1 range were hydroxyl-stretchingregionof baricite shows obtainedby the co-addition of 64 scans with a somewhatmore deŽ nition than the equivalent IR resolutionof 4 cm ­ 1 anda mirrorvelocity of spectrum.The spectral proŽ le in boththe Raman 0.6329cm/ s. andIR spectraextends to quitelow wavenumbers Spectroscopicmanipulation such as baseline forthe hydroxyl-stretchin gregion(Figs 1 and2). adjustment,smoothing and normalization were Boththe Raman and IR spectraof bobierriteshow performedusing the Spectracalc software package moredeŽ nition than for either vivianite or GRAMS (GalacticIndustries Corporation, NH, baricite.The Raman spectrum has bands at

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FIG.2. IRspectra of the hydroxyl-stretching region of ( a)vivianite, ( b)baricite and ( c)bobierrite.

3482,3263, 3096 and 2888 cm ­ 1. The IR bandat 1666cm ­ 1 suggeststhat water is strongly spectrumshows bands at 3475, 3432, 3150, hydrogenbonded to the phosphate oxygen. The 3039and 2895 cm ­ 1.Inthe crystal structure of bandat 1615 cm ­ 1 isassigned to the bending bobierrite,the distance between the oxygen and modeof water hydrogen bonded to water, whilst thehydrogen in theOH unitsvaries from 0.79 to theband at ~1586cm ­ 1 maybe attributedto non- 0.89 AÊ withan averagevalue of 0.84 A Ê (Takagi et hydrogenbonded water, equivalent to that found al., 1986).All the hydrogens are involved with forwater as water vapour. hydrogenbonding and it is this hydrogen bonding Itis apparent that in the molecular structure of whichholds adjacent sheets together. vivianite,three different types of water are observed.For baricite the IR spectrumshows a broadproŽ le similar to that observed for the WaterHOH bending hydroxyl-stretchingregion of baricite. Three TheIR spectraof the water HOH-bending mode bandsmayb eŽttedat1669,1631a nd isshown in Fig. 3 andthe data reported in 1589 cm ­ 1.Thedescription of these bands is as Table1. Forvivianite three bands are observed at forvivianite.The IR spectrumof bobierritein this 1666,1615 and 1586 cm ­ 1.Apreviousstudy has regionshows two bands resolved at 1655 and suggesteda singleband at 1620cm ­ 1(Piriou and 1587 cm ­ 1. The 1655 cm ­ 1 bandis assigned to Poullen,1987). Farmer (1974) reported the band thewater strongly hydrogen bonded to the at 1635 cm ­ 1.Importantlythe observation of the adjacentlayers. For this mineral no band for

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TABLE 1.Raman and IR spectralanalysis of the phosphates of thevivianite group.

Vivianite Baricite Bobierrite Raman IR Raman IR Raman IR Suggested * assignment

3496 3460 3400 3480 3498 3482 3475 Hydroxyl 3262 3281 3300 3373 3263 3432 stretching 3130 3104 3121 3168 3096 3150 3012 3025 2927 2895 3039 2867 1666 1635 1669 1655 Water HOH 1615 1631 1587 bending 1586 1589 1081 1053 1079 1040 1057 1100 1072 1089 POstretching 1050 1018 1027 990 953 1039 998 1034 1015 990 950 859 998 951 998 949 951 923 970 909 969 942 943 813 890 802 842 832 Water librational 783 872 787 modes 584 634 600 632 717 703 Out-of-plane 569 575 576 693 677 bends 545 561 560 545 668 530 492 527 631 583 557 542 456 461 468 In-plane 423 428 435 bends 390 420 344 340 364 307 314 318 281 281 290 282 262 236 243 233 186 212 215 201 182 170 170 140 149 136

*Published by Piriou and Poullen (1984)

adsorbedwaterat ~1620 to1630 cm ­ 1 was typesof watercan explain the number of bandsin observed.The band at ~1587 cm ­ 1 ascribed to theIR andRaman spectra. This explanation is non-hydrogenbonded water is attribute dto alsouseful to explain the bands at ~1630 and includedwater. In the unit cell of vivianite there ~1660 cm ­ 1.Howeverin the hydroxyl deforma- 2+ aretwo formula units (Fe 3 (PO4)2·8H2O) per unit tionregion,bandsareobservedaround cell since Z =2.This means that there are 16 1590 cm ­ 1,whichis the band position of non- watermolecules in the unit cell. Thus the two hydrogenbonded water. One possible explanation

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FIG.3. IRspectra of the water HOH-bending region of ( a)vivianite, ( b)baricite and ( c)bobierrite. couldbe offered in terms of  uidinclusions, Anyphenomenon such as the migration of a whichcould provide the explanationfor thisband. protonto a phosphateanion can be measured Inthehydroxyl-stretchin gregionin both the IR usingvibrationa lspectroscopy.Likewise the andRaman spectrum of vivianiteand bobierrite, a bondingof a hydroxylunit to the metal could be sharpband is observed at ~3490 cm ­ 1. The observed.Importantly-POH unitscould be intensityof the band is greaterin the IR spectrum. formed,the IR andRaman spectrum of which Onepossible explanation of thisband is thatit is mightshow its presence. SigniŽ cant intensity dueto hydroxyl groups associated with the existsin the bands at 3012 cm ­ 1 forvivianite, presenceof Fe 3+. 3025 cm ­ 1 forbaricit eand2895 cm ­ 1 for Bobierritemay contain some minor amounts of bobierrite.This latter band is quite distinct in Fe,which could also be oxidized. If some theRaman spectrum of bobierrite. One explana- oxidationof the ferrous ion to ferric occurs then tionof thisband is thatit isdue to the formation thischarge would need to be counterbalanced by ofthe -POH unitsand this band is the stretching thenegative of the hydroxyl unit as no other vibrationof this hydroxyl unit. negativecharge scouldorigin atefrom the phosphateanion. (Wildner et al., 1996) This PhosphatePO-stretchi ngregion thencould mean that a freeproton is availableto form HPO4 units.The following reaction is TheRaman and IR spectraof the phosphate envisaged. symmetricstretching region of vivianite, baricite 3 ­ 2 ­ ­ andbobierrite are shown in Figs 4 and5. The PO4 + H2O ? HPO4 + OH analysisof thespectral data is reportedin Table 1.

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FIG.4. Raman spectra of the phosphate-stretching region of ( a)vivianite, ( b)baricite and ( c)bobierrite.

Inthe Raman spectrum of vivianite, a single isborne out in the IR spectra.Infrared bands are intenseband is observed at 949 cm ­ 1 with low- observedat 1079, 1027, 950 and 923 cm ­ 1. The intensitybands observed at 1081, 1050 and 950 cm ­ 1 bandis the symmetric stretchi ng 1015 cm ­ 1. The 949 cm ­ 1 bandis assigned to vibrationalso observed in the Raman spectrum. theRaman active PO-stretching vibration. The Thetwo bands at 1079 and 1027 cm ­ 1 corre- positionof this band is in excellent agreement spondto the very low intensity Raman bands withthe previously published result (Piriou and observedat 1081 and 1050 cm ­ 1.Previously Poullen,1987). The bands at 1081, 1050 and publishedIR datareported by Farmergave bands 1015 cm ­ 1 areassigned to the phosphate PO at1040 and 990 cm ­ 1,whichare different from antisymmetricstretchingvibrations.The theresults reported here. One possibility is that 1081 cm ­ 1 bandis very low in intensity. Pirou thedata are correct and the identiŽ cation of the andPoullen found bands at 1053and 1018 cm ­ 1 mineralused by Farmer incorrect. andare in agreementwith our results. We did not Inthe spectra in Fig. 5 quiteintense IR bands observethe band at 990 cm ­ 1.Thephosphate areobserved at 813and 783 cm ­ 1.Thereare two anionin an aqueous solution shows a single possibilitiesfor the assignment of these bands: antisymmetricband at 1017 cm ­ 1.Inthis work Žrstthe position of the band at ~813 cm ­ 1 could threebands are observed, consistent with the beassigned to the AsO-stretchin gvibration. reductionof thephosphate ion symmetry from Td Howeverno band was observed at this position to C3v or less to C2v inaccord with the crystal inthe Raman spectrum and also the chemical structuredetermination. This symmetry reduction analysisusing the e lectronprob edidnot

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FIG.5. IRspectra of the PO 4-stretching region of ( a)vivianite, ( b)baricite and ( c)bobierrite. determinean As value, which was below the at1039, 998, 970 and 942 cm ­ 1.Abandis also detectionlimits. Bands in this position are observedat 802 cm ­ 1 andis assigned to water commonto all three minerals .Thesecond librationalmodes of strongly hydrogen bonded possibilityis the bands at 813 and 783 cm ­ 1 are watermolecules. The observation of four anti- dueto waterlibrational modes. Such bands would symmetricstretching vibrations is presumably a beintense in the IR spectrabut weak or of zero functionof both low symmetry and substitution of intensityin the Raman spectrum. The position of Fe by Mg. thesebands is very sensitive to hydrogen bonding. Inthe Raman spectrum of bobierrite (Fig. 4 c), Theobservation of more than one type of water anintense band is observed at 951 cm ­ 1. This moleculein the structure from the water bending bandis assigned to the PO symmetricstretching modesimplies that there should be morethan one vibration.Bands of low intensity are observed at waterlibrational mode. 1072,998 and 909 cm ­ 1.Low-intensitybands are TheRaman spectrum of baricite (Fig. 4 b) alsoobserved at 842 and 787 cm ­ 1. The IR displaysthree bands in the PO-stretching region spectrumof bobierrite (Fig. 5 c)isbetter deŽ ned at1057, 953 and 859 cm ­ 1.Thesimple descrip- thanthat of vivianite and baricite. Two distinct tionof these bands suggests that the 1057 cm ­ 1 regionsare observed centred upon bands in the bandis due to the PO antisymmetricstretching 900to 1100 cm ­ 1 regionand bands in the vibrationand the 953 cm ­ 1 tothe PO symmetric 850 cm ­ 1 regionand below. Five IR bandsare stretchingvibration. The IR spectrumof baricite observedat 1089, 1034, 998, 969 and 943 cm ­ 1. (Fig. 5b)asfor vivianite shows complexity. The 943 cm ­ 1 bandis assigned to thesymmetric Infraredbands in this spectral region are observed stretchingmode and the other four bands to the

1070 VIVIANITE-GROUPRAMAN AND INFRARED SPECTROSCOPY

antisymmetricstretching modes. Strong IR bands aqueoussolutions of the phosphate ion, the band ­ 1 ­ 1 areobserved at 832, 703 and 677 cm and are observedat 420 cm isassigned to the n2 assignedto water librational modes. bendingmode. For vivianite, two bands are observedat 423 and 456 cm ­ 1,withthe latter beingthe more intense. The observation of two Phosphatebending modes bandsfor the OPO bendingregion suggests the TheRaman spectrum of the low-wavenumber lossof degeneracy of the bending mode. For regionfor the three compositio nallyrelated baricitethree bands are observed for the n2 vivianitemineralsis shown in Fig. 6. The bendingmode at 461, 428 and 390 cm ­ 1. For resultsof the spectral analysis are reported in bobierritethree bands are observed at 468, 435 Table1. The use of the diamond ATR cellhas a and 420 cm ­ 1.Theonly Raman data for lowerwavenumber limit of ~600 cm ­ 1, and as a comparisonis that reported by GrifŽ th, who consequenceno IR datafor this region were suggestedthe bending mode was at 316 cm ­ 1 obtained.One of the main advantages of Raman (GrifŽth, 1970). However this seems to be an spectroscopyis the ability to obtain spectral data error.Farmer (1974) also did not report the below 400 cm ­ 1.ThedifŽ culty in the study of bendingmode. thisspectral region is a combinationof the Foraqueous systems the n4 modeof phosphate complexityof the overlap and the number of isobservedat 567 cm ­ 1.Forvivianite, four bands bands.The difŽ culty rests with the attribution of areobserved at 584,569, 545 and 530 cm ­ 1. The themultiple bands found in this region. In 569 cm ­ 1 bandis intense and sharp. These bands

FIG.6. Raman spectra of the low-wavenumber region of ( a)vivianite, ( b)baricite and ( c)bobierrite.

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areassigned to the n4 modesof vivianite. The AllanPring, (Principal Curator of Minerals,South spectraldata reported by GrifŽ th is at variance AustralianMuseum, North Terrace Adelaide, withthese results (GrifŽ th, 1970). Farmer SouthAustralia 5000) is thanked for the loan of reportedIR bandsat 590, 560 and 475 cm ­ 1 thebaricite and bobierrite minerals. (Farmer,1974). For baricit e, n4 bands are observedat 576, 545 and 527 cm ­ 1 and for References bobierrite,bands are found at 583, 557 and 542 cm ­ 1.Inthe Raman spectrum for vivianite, Anthony, J.W.,Bideaux, R.A.,Bladh, K.W.and twointense bands are observed at 236 and Nichols, M.C. (2000) Handbook of Mineralogy 186 cm ­ 1.Onepossibility is that these bands Volume IV: Arsenates, Phosphates and Vanadates . areattributable to FeO-stretching vibrations. This Mineral Data Publishing, Tuscon, Arizona, USA. spectralregion for baricite is complex. Two Farmer, V.C.(editor) (1974) The Infrared Spectra of intensebandsareobservedat203and Minerals.Mineralogical Society Monograph 4, 170 cm ­ 1.Forbobierrite, an intense band is 539 pp. observedat 215 cm ­ 1 andis assigned to the Gevork’yan, S.V.and Povarennykh, A.S.(1973) MgO-stretchingvibration. Vibrational spectra of some iron phosphate hydrates. Konstitutsiya iSvoistva Mineralov , 7, 92 ­ 99. Gevork’yan, S.V.and Povarennykh, A.S.(1980) Conclusions Characteristics of the IRspectra of water molecules incorporated into phosphate and arsenate structures. Acombinationof Ramanand IR spectroscopyhas Mineralogicheskiy Zhurnal, 2, 29 ­ 36. beenused to study a compositionallyand GrifŽth, W.P.(1970) Raman studies on rock-forming structurallyrelated set of vivianite phosphate minerals. II. Minerals containing MO 3, MO4, and MO6 minerals.Bands attributed to the water hydroxyl groups. Journal of the Chemical Society, A , 286 ­ 291. stretching,bending and librational modes are Henderson, G.S., Black, P.M., Rodgers, K.A.and identiŽed andshow the existence of threetypes of Rankin, P.C.(1984) Newdata on NewZealand watermoleculesin th estructure,namely vivianite and metavivianite. NewZealand Journal of adsorbed,weakly and strongly hydrogen-bonded. Geology and Geophysics , 27, 367 ­ 378. Asinglephosphate symmetric stretching vibration Hunt, G.R.(1977) Spectral signatures of particulate isobse rvedfor ea chminera lbutse veral minerals in the visible and near infrared. Geophysics, antisymmetricstretching modes are observed 42, 501 ­ 513. consistentwith a lossof symmetry of the Hunt, G.R., Salisbury, J.W. and Lenhoff, C.J. (1972) phosphateanion in the mineral crystals. The loss Visible and near-infrared spectra of minerals and ofsymmetry also results in several in-plane and rocks. V.Halides, phosphates, arsenates, vanadates, outof plane bending modes. Vivianite is an and borates. Modern Geology , 3, 121 ­ 132. intenseblue colour whilst baricite and bobierrite Melendres, C.A., Camillone, N., III and Tipton, T. varyfrom colourless to blue. The observation of (1989) Laser Raman spectroelectrochemical studies bluemateria lsin so ilsand sedimen tshas of anodic corrosion and Žlm formation on iron in suggestedthe use of Raman spectroscopy for the phosphate solutions. Electrochimica Acta , 34, identiŽcation of vivianite in these soils. It is 281 ­ 286. suspectedthat the other two minerals exist in Omori, K.and Seki, T.(1960) Infrared study of some phosphate minerals. Ganseki Kobutsu Kosho groundwaterdrainage sites but this remains to be Gakkaishi, 44, 7 ­ 13. proved.Such minerals have been found in Piriou, B.and Poullen, J.F. (1984) Raman study of sedimentsfrom New Zealand.This study demon- vivianite. Journal of Raman Spectroscopy , 15, stratesthat Raman and IR spectroscopycan be 343 ­ 346. usedto distinguish the vivianite Fe-Mg phosphate Piriou, B.and Poullen, J.F. (1987) Infrared study of the phasesby their spectra. vibrational modes of water in vivianite. Bulletin de Mineralogie , 110, 697 ­ 710. Acknowledgements Sitzia, R.(1966) Infrared spectra of some natural phosphates. Rendiconti Seminario della Facolta di TheŽ nancialand infrastructural support of the Scienze, Universita di Cagliari , 36, 105 ­ 115. QueenslandUniversity of Technology Centre for Takagi, S., Mathew, M.and Brown, W.E. (1986) Crystal Instrumentaland Developmental Chemistry is structuresofbobierriteandsynthetic gratefullyacknowledged.TheAustralian Mg3(PO4)2.8H2O. American Mineralogist , 71, ResearchCouncil is thanked for funding. Prof. 1229 ­ 1233.

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Wildner,M.,Giester, G.,Lengauer, C.L.and Wolfe, C.W. (1940) ClassiŽcation of minerals of the McCammon, C.A.(1996) Structure and crystal type A3(XO4)2.nH2O. American Mineralogist , 25, chemistry of vivianite-type compounds: crystal 738 ­ 754, 787 ­ 809. structures of erythrite and annabergite with a Mo¨ssbauer study of erythrite. European Journal of [Manuscript received 15 June 2002: Mineralogy, 8, 187 ­ 192. revised 9October 2002 ]

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