Spectrochimica Acta Part A 59 (2003) 2247 /2266 www.elsevier.com/locate/saa
Catalogue of 45 reference Raman spectra of minerals concerning research in art history or archaeology, especially on corroded metals and coloured glass
M. Bouchard *, D.C. Smith
Baˆtiment Mine´ralogie, Muse´um National d’Histoire Naturelle and CNRS, 61 Rue Buffon, 75005 Paris, France
Received 23 June 2002; accepted 15 August 2002
Abstract
Small catalogues of reference Raman spectra of interest for analysing geomaterials or biomaterials of relevance to art history or archaeology are gradually being published by different research groups. However, except for some older catalogues, they are all concerned primarily with pigments, whether inorganic or organic. Here we present for the first time a catalogue of Raman spectra of minerals that may be found in corroded metal artworks or artefacts. At the same time we include some inorganic pigments that may be found in or on stained glass. Most of the minerals analysed came from the Gallery of Mineralogy at the Muse´um National d’Histoire Naturelle and most were verified by X-ray diffraction in order to augment the confidence in the mineral identity (which is not the case with many other catalogues). A number of problems encountered with mineral terminology are discussed. Comments are made on the spectra where appropriate. # 2003 Elsevier B.V. All rights reserved.
Keywords: Raman spectroscopy; Catalogue; Reference spectra; Art; Archaeology
1. Introduction and tissues), the whole having been defined as ‘ARCHAEORAMAN’ [1,2], is the lack of ade- A major problem for a relatively ‘young’ quate databases of ‘reference Raman spectra’, i.e. discipline such as non-destructive Raman Micro- spectra obtained from known inorganic, organic scopy (RM) applied to Archaeology and Art or amorphous species. The basis of species identi- History in general, i.e. not only to pigments but fication by RM is the comparison of the spectrum also to geomaterials (e.g. rocks, gems, ceramics, of an unknown material with reference spectra glass and metals) and to biomaterials (e.g. resins (‘Raman spectral fingerprinting’). A poorly-docu- mented database will thus handicap any identifica- tion. Very few databases existed until recently: by * Corresponding author. Tel.: /33-1-4079-3527; fax: /33-1- Griffith on crystals [3], Guineau on pigments [4], 4079-3524. E-mail address: [email protected] (M. and Pinet et al. on gemstones [5]. Since then the Bouchard). database on pigments by Bell et al. [6] has been
1386-1425/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00069-6 2248 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266 updated by Burgio and Clark [7] and a consider- cm 1, the samples were simply placed in turn in able number of new research teams are building up the exciting laser beam under the microscope their own databases on pigments. objective. The Raman spectra were mostly mea- We decided in 1997 to prepare a new database sured with the following operational conditions: concerning products likely to be observed in two red He/Ne laser excitation at 632.8 nm; 30 mW new domains of RM archaeometrical research: laser power at source reduced considerably by corrosion products of metals (e.g. sculptures, various filters and by the optical trajectory; /10, weapons or tools), and pigments and alterations /50 or /100 objective; 300 mm slits; multi- of stained glass (e.g. windows). The prestigious channel CCD detection; integration time 50 /400 mineral collection of the Gallery of Mineralogy of s and two to seven accumulations. Green Ar the MNHN provides an excellent selection of laser radiation at 514.5 nm was also sometimes thousands of natural mineral species. Most of the used with variable but low laser power to reduce spectra presented in this catalogue came from heating of the sample. For routine analysis, 9/3 samples of this collection and most of these cm 1 is considered to be the accuracy when minerals were checked by X-ray powder diffrac- comparing spectra from different samples, on tion (XRD) to verify that their Museum labelling different days, or from different instruments; the 1 was correct [8]. Most of the modern pigments here precision of RM being around 9/1cm . The were kindly provided by the ‘Atelier Debitus’ spectra published here were sometimes established stained-glass factory at Tours, France, but several by the simple addition of one spectrum obtained had previously been purchased by them from with the laser beam polarisation vertical and one commercial pigment manufacturers. with the laser beam polarisation horizontal, with- The Raman spectral data are presented below in out moving the sample at all, in order to take an identical format. Each paragraph starts with account of the crystal axis orientation effect and of the F codenumber that gives the ‘fiche’ (file or the optical trajectory orientation effect [9]. The index card) number of the corresponding XRD spectra presented were sometimes treated by base- data (the sign £ for confirmed spectra and no sign line correction and/or minor smoothing. for non-confirmed spectra). The XRD data are available from the authors. This is followed by the mineral group name, mineral species name, ideal chemical composition, crystal system and space 3. Terminological and other problems group. The second line lists the observed Raman wavenumbers, with underlining indicating the In all cases where it was possible to extract a relatively stronger bands and an asterisk the minute portion of crystal from the Gallery, an weaker ones (or shoulders). All the plotted spectra XRD identification was carried out to confirm the appear in Fig. 1 and can be identified by their F nature of the mineral species by reference to codenumber as well as their mineral species name. international powder diffraction tables. A consid- The order of the mineral species is based on erable number of problems were encountered and mineral groups as shown in Table 1 where an our procedure for dealing with them is outlined alphabetical list is also supplied. For simplicity the below. Over 70 species were collected from the adjectival term ‘hydroxy-’ here includes minerals Gallery or the ‘Atelier’ but only 45 finally arrived with (OH) and/or H2O. in this catalogue.
1) Minerals in the Gallery, being natural miner- 2. Experimental als, are very often mineral mixtures and whereas it was usually obvious to an experi- The Raman Microscope employed was a enced mineralogist which was which, this DILOR† XY† instrument. After wavenumber was not always the case and it was then calibration using the diamond peak at 13329/1 necessary to analyse each of the mineral M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266 2249
Fig. 1. The Raman spectrum obtained from each of the 45 minerals described in this catalogue, each one being labelled by the species name preceded by our computer code F number as used in the text. Abscissa: wavenumber in cm 1. Ordinate: arbitrary units. 2250 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
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Fig. 1 (Continued) 2254 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
Fig. 1 (Continued) M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266 2255
Fig. 1 (Continued) 2256 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
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Table 1 species present (e.g. a sample labelled ‘man- Mineral species names and F codenumbers arranged by mineral ganite and polianite’). group and also alphabetically 2) The polymineralic situation also occurred Lexicon arranged by Alphabetical lexicon when only one species was listed as being mineral group present (e.g. in a sample labelled ‘anglesite’
Oxides Anglesite F17 the results revealed a rather large quantity of F1*/Cuprite Antlerite F13 cerussite coupled with only a small amount F2 */Hematite Atacamite F25 of anglesite; likewise ‘langite’ was in fact F3 */Litharge et massicot Aurichalcite F38 F4 */Minium Azurite F35 brochantite with a little langite). F5 */Zinc oxide Boleite F30 3) No exploitable Raman spectra were obtained F6 */Zincite Botallackite F27 F7 */Cassiterite Brochantite F15 due to the great opacity of certain minerals, F8 */‘Cobalt oxide’ Buttgenbachite F43 and sometimes due to the Raman selection F9 */Eskolaite Calumetite F28 rules (e.g. no data from the samples labelled: Oxy-Hydroxides Cassiterite F7 F10 */Goethite Cerussite F3 ‘chalcocite’, ‘eurubexite /chalcopyrite’ (in F11 */Lepidocrocite Chalcanthite F14 fact bornite by XRD analysis), ‘acanthite’, F12 */Manganite Chlorargyrite F23 (Cerargirite) ‘galena’, ‘chlorargyrite’, ‘melanothallite’, Sulphates and hydroxy- Clinoatacamite F26 ‘percylite’, and ‘chrysocolla’). sulphates 4) When the XRD spectrum did not correspond F13 */Antlerite Cobalt oxide F8 F14 */Chalcanthite Connellite F42 to the species name on the sample label, then F15 */Brochantite Cotunnite F23 two possible situations arose: F16 */Linarite Covellite F18 F17 */Anglesite Cumengite F29 i) If the new XRD identification pre- Sulphides Cuprite F1 sented some interest, then the sample F18 */Covellite Dioptase F41 was reallocated a new correct name Phosphates and hydroxy- Eskolaite F9 phosphates and the Raman spectrum was recorded F19 */Libethenite Fiedlerite F31 under the new name (e.g. the pre- F20 */Pseudomalachite Goethite F10 Chlorides and hydroxy- Hematite F2 viously-labelled sample ‘brochantite’ chlorides turned out to be antlerite by XRD). F21 */MOLYSITE Hydrocerussite F37 ii) If the new XRD identification pre- F22 */Matlockite Hydrozincite F40 F23 */Cotunnite Laurionite F32 sented no interest, then that sample F24 */MENDIPITE Lepidocrocite F11 was abandoned and one tried to find F25 */Atacamite Libethenite F19 F26 */Clinoatacamite Linarite F16 another sample of the desired species. F27 */Botallackite Litharge and massicot F3 5) It should, however, be borne in mind that the F28 */Calumetite Malachite F36 international XRD database may not neces- F29 */Cumengite Manganite F12 F30 */Boleite Matlockite F22 sarily be 100% correct such that one must be F31 */Fiedlerite Mendipite F24 aware of the possibility of error there, even if F32 */Laurionite Minium F4 Carbonates and hydroxy- Molysite F21 only rarely. Indeed RM is an excellent carbonates technique for complementary studies with F33 */Cerussite Phosgenite F44 XRD and might be able to resolve any F34 */Smithsonite Pseudomalachite F20 F35 */Azurite Pyromorphite F45 difficulties arising with the XRD database. F36 */Malachite Rosasite F39 6) It may also be noted that a method avoiding F37 */Hydrocerussite Smithsonite F34 F38 */Aurichalcite Tenorite F2 the need for confirmation by XRD was F39 */Rosasite Zincite F6 developed by Smith in his database ‘RAMA- F40 */Hydrozincite Zinc oxide F5 Hydoxy-silicates NITA’ [1,10]. There a multitude of spectra F41 */Dioptase from different samples, different spectro- Mixed phases meters and different analysts, but of the F42 */Connellite F43 */Buttgenbachite same ‘supposed’ species, are tabulated and F44 */Phosgenite a statistical approach gives a degree of F45 */Pyromorphite certainty about the identity of the species. 2258 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
7) Another major problem concerns the official problem still remains since the old International Mineralogical Association name may persist on old labels. (IMA) nomenclature of mineral species. ii) An old name may be found to corre- Indeed, if one considers the year of acquisi- spond to another approved species, but tion of certain studied minerals (this varies again the old name may persist on old between the beginning of the XIXth century labels or something else may be found up to today) one may consider that their to be wrong with the original descrip- allocation to such or such mineral species as tion (e.g. a sample labelled ‘xanthosi- being doubtful in several cases. This situa- derite’ turned out to be a mixture of tion unfortunately arose frequently, but it is, goethite and lepidocrocite, and xantho- however, not appropriate to automatically siderite itself is not an approved name impute these errors of terminology to the anyway). mineral collectors, amateurs or professional, 9) A variability of Raman spectral results from who helped in the constitution of the current different authors for the same analysed Gallery. The following examples relate the species could obviously be due to instrumen- fragility and the historical inconsistency of tal differences between the various research the physico-chemical and mineralogical char- teams, but it may well be due to error of acterisations of mineral species: some kind, such as a non-calibrated spectro- i) Early in the XIXth century a petrogra- meter or an incorrect interpretation of spec- tra (e.g. the 843 cm 1 luminescence band of phical confusion occurred which dis- the OLYMPUS /50 objective is often turbed the mineralogical nomenclature mistakenly considered as a Raman band of of the iron oxyhydroxides goethite the analysed material). (a-FeOOH) and lepidocrocite (g- 10) The purity, or even the honesty, of certain FeOOH); an inversion occurred such commercial pigment samples is often in that goethite was named lepidocrocite question. One case concerning the pigment and inversely. Thus ancient labels may ‘Naples yellow’ is very representative. Three say the opposite of recent ones. supposed commercial samples of Pb2(SbO4)2 ii) Cu2Cl(OH)3 had long been known to were analysed [12]: the first one gave a lead haveseveral polymorphs in addition to antimony oxy-hydroxide [Pb2Sb2O6(O,OH)]; atacamite, but it was not until 1996 the second was constituted by the same that clinoatacamite was established and hydroxide with Sb2O3 in addition; the third shown to be the same as what others one was composed of PbCO3 and PbCrO4. had previously called paratacamite Thus not one of three samples corresponded [11], and that paratacamite was shown to the expected formula. A recent RM and to exist but to need some zinc [11]. The FTIR study of commercial pigments [13] confusion between these two poly- again demonstrated that some pigments morphs, whereby many earlier analyses were not at all what they were supposed to of clinoatacamite were misnamed para- be, and indeed the ‘cobalt blue’ acquired tacamite, probably concerns a large from seven (!) sources was in every case not number of studies made before 1996. the same substance! 8) The IMA occasionally officially discredits an 11) Nearly last but not least, the yawning gap of earlier name that thus becomes banned. terminological usage between (a) prehistor- Again there are two situations. ians/historians, archaeologists and artists, (b) i) If the correction of the labelling some- chemists, physicists and spectroscopists, and times appeared to be straightforward (c) crystallographers, mineralogists and geol- (e.g. the IMA change of a sample ogists, is also a major problem. For example labelled ‘chessylite’ into ‘azurite’), a if (a) says ‘vermilion’, (b) says ‘mercury M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266 2259
sulphide’ or ‘HgS’, and (c) says ‘cinnabar’. 4. Catalogue Likewise (a) may use ‘ochre’ or ‘red ochre’ or ‘iron ochre’ or ‘Mars red’, but (b) uses ‘iron 4.1. Oxides oxide’ or ‘Fe(III) oxide’ or ‘ferric oxide’ or
‘alpha ferric oxide’ or a-Fe2O3, and (c) 4.1.1. F1*/Cuprite, Cu2O, cubic, Pn3m; £ ‘haematite’. Only the last is IMA-approved, Raman bands (wavenumbers): 638*, 495*, 218; and it is both necessary and sufficient to 195, 186, 148, 93, 55 cm 1. define both the chemical composition and
the physical structure of a mineral species. 4.1.2. F2*/Haematite, a-Fe2O3, trigonal, R3c/ Analytical techniques like RM and XRD Raman bands (wavenumbers): 1330, 611, 498, give the species directly from the spectrum or 411, 299*, 291; 245, 224 cm 1. diffractogram (e.g. cinnabar or haematite); Since all the studied Gallery samples of haema- they do not give directly colours like vermi- tite were monocrystals, it was not possible to make lion or ochre, nor elements like Hg or Fe. XRD powder analysis; nevertheless, by deduction Many pigments are in fact complex mixtures and comparison with other Raman spectra of (e.g. Egyptian Blue, Maya Blue, Red Ochre) guaranteed haematite, the Raman spectrum pre- and these names should only be given if one sented here belongs with certainty to haematite. has found all of the different phases of the Haematite is the most stable kind of iron oxide. mixture. According to the literature there exist numerous 12) Many pigments do not have a mineral name possible natural substitutions of Fe by Cr, Mn and (for which a natural occurrence is obligatory Ti but mainly by Al. under IMA rules), e.g. ‘Prussian Blue’ is Water in the form of OH groups can exist in iron(III) hexaferrocyanate(II) [Fe4(Fe- poorly-crystallised haematite. Some of these (CN)6)3] ×/ 14 /16H2O [7]; ‘cobalt blue’ is a groups may disappear if the temperature exceeds cobalt(II)-doped alumina glass [7]. 160 8C whereas others do not disappear until 13) Finally, the names given to pigments may 1000 8C. The replacement of O by OH (hydro- vary according to the historical period or to haematite of Wolska and Schwertmann [15],or the specific recipe of every single artist or protohaematite of Waychunas [16]) is compen- painter. Here the sentence of Pastoureau [14] sated by cation vacancies according to certain becomes most fitting: ‘‘the colour of the authors. painter is not that of the physicist, and that Haematite is now well-identified and defined of the physicist is not that of the poet’’. and numerous Raman studies have been made on corrosion products of iron objects, or of Fe- Despite this long list of difficulties, we believe bearing pigments. Most of the authors admit the that the analyses obtained here with combined seven characteristic bands of haematite presented
RM and XRD have allowed the obtention of exact in the table above as well as the band at 1310 /1330 identifications of the minerals, and hence of cm 1 which corresponds to a ‘two-magnon’ effect. ‘reference Raman spectra’, in almost all cases, The band at 660 cm 1 is at the same wavenumber but the reader will understand that perfection as that of magnetite and it has been suggested that cannot be guaranteed. it exists in the Raman spectra of haematite because The database described here, which of course is of partial transformation into magnetite under the still far from being comprehensive, is presented as laser beam [8]. a considerable improvement of the pre-existing It is to be noted that the Raman bands quoted situation; it provides a battery of spectral data here are characteristic of a well-crystallised hae- which ought to be of use to researchers working on matite. The band at 411 cm 1 is particularly non-destructive RM analysis of corroded metals sensitive, among other things, to the variations or coloured glass, and probably on other kinds of caused by hydration, or by other substitutions (e.g. artefact or artwork. Al, Mn), or by the temperature of the sample. 2260 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
4.1.3. F3*/Litharge (tetragonal, P4=nm) and increases. Thus the strong narrow band at 437 Massicot (orthorhombic, Pbma,) PbO, £ cm 1 is a good indicator of order. 1 Raman bands (wavenumbers) litharge (L) / The bands at 1150 and 1076 cm are attributed massicot (M): 426*, 387(M), 342(L), 291(L /M), to a multiphoton effect [19]. A minor pollution by 1 148(L), 144(L /M), 89(M), 84, 73(M) cm . hydrozincite could explain the presence of three The upper spectrum is a mixture of litharge (L) more bands at 1062, 1371*, 1550* cm 1 (cf: F40); and massicot (M); the lower spectrum is massicot this hypothesis could also justify the presence of alone. If there are numerous methods to obtain the O /H vibrations bands observed here at 3573, ‘lead protoxide’ or PbO (e.g. by dry methods: 3509, 3413 cm 1. Regrettably, no spectrum of the pyrolysis of oxides, hydroxides or lead carbonates, O /H bands of hydrozincite was able to be or by wet methods: electrolysis), the nature of the acquired in this zone of wavenumbers, so we product collected at ambient temperature depends cannot, with certainty, attribute these three bands on the conditions of cooling, the grain dimensions, to vibrations of the O /H bonding of hydrozincite and the form and the degree of perfection of or to that of water adsorbed on crystals of ZnO, a crystallites formed at high temperature ( / phenomenon already recorded by Philips [20]. 448 8C). A slow cooling tends to produce the most thermodynamically stable form at ambient 4.1.6. F6*/Zincite, (Zn,Mn)O, hexagonal, / temperature: litharge (red), a-PbO, while a more /P63mc/, £ rapid cooling tends to preserve the other form: Raman bands (wavenumbers): 571, 543, 525; massicot (yellow), b-PbO [17]. In practice, and 480 cm 1. according to Pascal [17], one obtains a mixture of The differentiation by RM between zinc oxide both polymorphs. Our attributions of bands given and zincite is not an easy matter. Indeed, zincite above corresponds to those of Bell et al. [6]. The has hardly been studied by RM whereas zinc oxide presence of lead carbonates (cerussite, hydrocer- has already been the object of some researches ussite or plumbonacrite) was also revealed by RM [6,19]. On the other hand, these two minerals only thanks to the presence of weak bands at the differ in their chemical formulation by the variable wavenumbers 1051 and 1054 cm 1. presence of manganese in zincite [(Zn,Mn)O] [21], whereas this element is absent in pure zinc oxide
4.1.4. F4*/Minium, Pb3O4, tetragonal, P4b2; £ (ZnO). Raman spectra obtained on four different
Raman bands (wavenumbers): 549; 480, 391, natural samples labelled ‘zincite’ (ref. 98 /463, 98 / 1 313, 223, 150, 120; 84, 70, 60, 51 cm . 438, 58 /18 and 68 /192) gave three types of The major bands of the spectrum are at 120 different Raman spectra. Two of these samples 1 cm , which corresponds to the vibrations of (98 /463 and 98 /438) were confirmed by XRD IV deformation of the angle O /Pb /O, and at 549 analysis as being of pure zincite and are presented cm 1 which corresponds to the vibrations of in this article. The differences between zincite and IV elongation of the Pb /O bond [18]. ZnO are particularly characterised by the Raman bands at 480, 525 and 543 cm 1 in zincite only, as 1 4.1.5. F5*/Zinc oxide, ZnO, £ well as by the band observed at 571 cm in Raman bands (wavenumbers): 1150, 1076, 658*, zincite compared with 582 cm 1 in ZnO. These 582, 437; 410*, 380, 330 and 205* cm 1. bands of zincite ((Zn,Mn)O) can be well compared These bands correspond perfectly with the with those of Mn oxides like MnO and MnO2 observations of Bell et al. [6] and Xu et al. [19]. situated at 521 and 547 cm 1 for MnO and at 490, 1 This last author notably showed the variations of 523 and 576 cm for MnO2 [22], suggesting that intensity of the bands at 437 and 580 cm 1 the noticed resemblances come from the bands according to the temperature at which the sample corresponding to various vibrations of Mn /O is subjected. Thus, with cooling from 873 to rather than of Zn /O. The bands at 1596, 1094 2938K, the intensity of the band at 580 cm 1 and 1069 cm 1 can be attributed to multiphoton decreases, while that of the band at 437 cm 1 effects or to a minor pollution by hydrozincite. M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266 2261
The second of these zincites (98 /438) presents, in 4.2. Oxy-hydroxides addition to the already-mentioned bands, certain characteristic bands of ZnO (205, 330, 379, 410 1 and 437 cm ). Concerning sample 68 /192, 4.2.1. F10*/Goethite, a-FeOOH, orthorhombic, certain notorious differences in the spectra (both Pbnm, £ Raman and XRD) of this mineral allow us to Raman bands (wavenumbers): 552, 485, 387; assert that it is some other species. 300, 247, 92 cm 1. Goethite is the most stable and most common 3 4.1.7. F7*/Cassiterite, SnO2, tetragonal, P4=mnm; iron oxy-hydroxide. Fe in octahedral coordina- £ tion can be the object of substitutions by metal 3 Raman bands (wavenumbers): 842, 776, 635; ions, mostly by Al whose atomic radius (0.53 A˚ ) 3 475 cm 1. is lower than that of Fe (0.64 A˚ ). This replace- ment can be up to 33% Al. These factors influence the unit cell parameters, as well as the bonding of 4.1.8. F8*/‘Cobalt oxide’, Cox Oy hydrogen, and can constitute one of the causes of Raman bands (wavenumbers): 682, 478, 193 the variations observed when comparing spectra. 1 cm . Cation vacancies were also noted in the structure Ores rich in cobalt are rare. One finds especially of goethite [15]. We observed and identified the arsenides, sulphides and arseniosulphides such as structure of a ‘disordered’ goethite, characterised cobaltine CoAsS, in which the cobalt is generally with regard to a normal goethite by wide Raman associated with iron and nickel. Either divalent, or bands along with a band at precisely 400 cm 1, trivalent, cobalt reacts under heat with halogens, too high for pure goethite and too low for pure oxygen, sulphur, and is attacked by acids. Un- haematite [23].Even if goethite is the most stable changing in ambient temperature, cobalt oxidises iron oxy-hydroxide, some ambiguous variations in 2 in red heat and gives Co3O4. Salts of Co are the crystal structure of the alteration products of stable in air. The oxide CoO, by fusion with an iron give rise to a variability within the Raman acid oxide, gives defined compounds of which spectra of goethite, for example: 685, 550, 479, some have been used, sometimes since a long time 385, 299, 243 cm 1 [24]; 393, 307 [25]; 545, 515, ago (Nippour’s-1500 BC-), as pigments in painting 478, 413, 399, 386, 374, 312, 298, 284, 241*, 232, (cobalt blue) or as colour of ceramic fire. It is the 215 cm 1 [26]; 550, 474, 414, 397, 298 cm 1 [27]; case of ‘smalt’ (silicate of cobalt), of ‘blue The- 554, 387, 299 cm 1 [28]. The band at 92 cm 1, nard’ (aluminate of cobalt), of ‘blue azure’ (stan- identified in Bouchard [29] and Smith et al. [23], nate of cobalt), of ‘turquoise blue green’ seems to havenever been recorded, probably (aluminate and chromate of cobalt). ‘Rinmann’s because of its low wavenumber. green’ and ‘the pink of cobalt’ are mixtures, respectively, of cobalt oxide CoO with zinc oxide ZnO and of CoO with MgO. Salts of Co3 are strong oxidisers; they are thus unstable in solution. 4.2.2. F11*/Lepidocrocite, g-FeOOH, orthorhombic, Amam, £ The hydrated sesquioxyde Co2O3 is an amphoteric Raman bands (wavenumbers): 530, 379; 252 oxide: acid oxide, it gives cobaltites; basic oxide, it 1 gives cobaltic salts. The Co3 ion gives numerous cm . complexes, the most important of which are This is the stable polymorph of goethite. The cobaltiamines, cobalticyanides and cobaltinitrites. Raman bands of lepidocrocite are well established in literature, even if one again observes some fluctuations in the results of certain authors, for 1 4.1.9. F9*/Eskolaite, Cr2O3, trigonal, R/3¯/c, £ example: 1303, 650, 522, 493, 373, 245 cm [24]; Raman bands (wavenumbers): 607, 550; 347, 393, 257 cm 1 [25]; 380, 252 cm 1 [27]; 376, 250 305 cm 1. cm 1 [28]. 2262 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
4.2.3. F12*/Manganite, g-MnOOH, monoclinic, B/ SO4(OH)6) being differentiated only by an addi- 21//d, £ tional H2O group. Their mineralogical differences Raman bands (wavenumbers): 622, 558; 530, are more obvious (monoclinic 2/m for brochantite, 490*, 387, 357 cm 1. whereas orthorhombic Pc for langite). The RM In spite of the strong opacity of this black analysis of this micro sample did not find the coloured mineral, it was possible to record a crystals of langite identified by XRD; this fact Raman spectrum by using a very weak intensity evokes well the fragility of an interpretation based laser (1 mW) and a longer duration than that upon spot analyses only. which was imposed on the other samples (500 s). The Raman spectrum of this sample presented The obtained spectrum corresponds perfectly to above could be correlated with the Raman spec- that presented for this product by Bernard et al. trum of brochantite published by Schmidt and [22]: 620, 555, 528, 388, 358 cm 1. Lutz [31].
4.3. Sulphates and hydroxy-sulphates 4.3.4. F16*/Linarite, CuPbSO4(OH)2, monoclinic, P/21//m, £ 4.3.1. F13*/Antlerite, Cu3SO4(OH)4, Raman bands (wavenumbers): 3471, 3448, 3220, orthorhombic, Pnam, £ 1141, 1019, 968; 818*, 632, 610, 594, 513, 461, 436, Raman bands (wavenumbers): 3579, 3487, 1171, 365, 345, 326*, 230, 163 cm 1. 1133, 1078; 989; 785, 750, 629, 603, 501, 483, 469,
444, 417; 339, 297, 266, 249, 231, 172, 146, 125 4.3.5. F17*/Anglesite, PbSO4, orthorhombic, 1 cm . Pbnm, (£ /trace of cerussite in the XRD pattern) Raman bands (wavenumbers): 1060*, 982; 643, 1 4.3.2. F14*/Chalcanthite, CuSO4 ×/ 5H2O, triclinic, 608, 453; 442, 134* cm .
P/1¯; £ Raman bands (wavenumbers): 3482, 3345, 3206, 4.4. Sulphides 1143, 1096, 986; 612, 465, 426, 332*, 281, 202, 135, 1 124 cm . 4.4.1. F18*/Covellite, CuS, hexagonal, P/63//mmc, The OH vibration range shows an extremely- £ wide band typical of H2O. Raman bands (wavenumbers): 470; 263, 61 cm 1.
4.3.3. F15*/Brochantite, Cu4SO4(OH)6, monoclinic, 2//m, £ 4.5. Phosphates and hydroxy-phosphates Raman bands (wavenumbers): 3585, 3563, 3398,
3369, 3252, 1125*, 1098, 1078, 974; 911, 785*, 4.5.1. F19*/Libethenite, Cu2PO4OH, 769*, 730*, 621, 611, 597, 506, 483, 449, 429, 389, orthorhombic, Pnnm, £ 366, 319, 243, 233*, 195, 171 cm 1. Raman bands (wavenumbers): 3469, 1070*, A sample labelled ‘langite’ was shown to be 1051*, 1021; 1011, 975, 870, 627, 587, 557, 388*, mostly brochantite when analysed by XRD. This 302, 226, 195, 153 cm 1. demonstrates very well the long confusion that has concerned this mineral. Indeed, it was once 4.5.2. F20*/Pseudomalachite, Cu5(PO4)2(OH)4, considered wrongly as being identical to brochan- monoclinic, P/21//a, £ tite; today, langite is considered as a dimorph of Raman bands (wavenumbers): 3432, 3389, 1086, wroewolfeite [30]. 1060, 1001, 974, 866, 802, 747, 609, 520, 482, 452, XRD analysis of this sample gave a majority of 438, 368, 260, 211, 186, 176 cm 1. peaks of brochantite as well as four minor peaks In both copper phosphate alteration products attributable to langite. These two minerals are very presented above (pseudomalachite and libethenite) similar in their chemical formulation (langite: one can easily distinguish bands attributable to the 3 Cu4SO4(OH)6 ×/ H2O and brochantite: Cu4- group PO4 with wavenumbers close to those of a M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266 2263
free tetrahedron (v1 /969, v4 /595 and v3 /1046 4.6.4. F24*/Mendipite, Pb3O2Cl2, orthorhombic, 1 cm ) [32]. The slight variations of wavenumber P/212121/ positions of these bands, with respect to the Raman bands (wavenumbers): 3504, 732*, 601*, theoretical bands of the free group, are due to 474*, 435, 330, 273, 134 cm 1. 1 the different bonds of PO4 with the other compo- The band at 3504 cm is typical of O /H nents of the mineral. vibration suggesting that this sample is actually hydrated. 4.6. Chlorides and hydroxy-chlorides
4.6.5. F25*/Atacamite, Cu2Cl(OH)3, 4.6.1. F21*/Molysite, FeCl3, trigonal, R/3¯/ orthorhombic, Pmcn, £ Raman bands (wavenumbers): 667*, 598*, 373*, Raman bands (wavenumbers): 3433, 3349, 3329, 293; 259* cm 1. 974, 911, 843, 820, 595*,512, 449, 411, 358, 266, The problem of iron chlorides evokes the same 218, 149, 139* cm 1. problem as for copper chlorides [8]. This type of alteration, extremely dangerous for iron objects, is 4.6.6. F26*/Clinoatacamite, Cu Cl(OH) , very difficult to study as it is particularly unstable 2 3 monoclinic, P/2 //n, (£ in mixture of thermodynamically under its anhydrous form. The 1 clinoatacamite /atacamite) sample of molysite from the Gallery of Mineralogy Raman bands (wavenumbers): 3442, 3355, 3310, of the MNHN is preserved from air inside a glass 930, 911, 896, 842*, 820*, 804, 590, 511, 450, 420, box. Hence, no analysis by XRD could be made 364 cm 1. on this sample. It may be noted that the obstacle The state of the literature dealing with RM constituted by the glass box did not really repre- applied to the identification of atacamite, clinoa- sent a problem for an analysis by MR. Indeed, one tacamite or paratacamite is relatively poor and the of the advantages of this method is the capability comparison of Raman spectra of the various of analysing objects through any transparent polymorphs in the literature is non-existent until material. Exceptionally, this sample was analysed the present article (and further work in prepara- with the optical fibres and remote head of a tion) which constitutes the first study of the KAISER† Holoprobe† Mobile Raman Micro- distinction by RM of these species of hydrated scope (MRM) [2]. Regrettably, considering the copper chloride. There was of course the work of lack of documentation concerning the study of this Guineau [4] that dealt with atacamite and with type of alteration product by MR, the acquired what he called ‘paratacamite’; however, his results spectra cannot be compared for confirmation. do not correspond exactly to ours, and the Nevertheless, Colthrup et al. [33] indicated that anteriority of Guineau’s work with respect to the bond M /Cl (where M is a metal) is observed in that of Jambor [11] (see Section 3) leads us to Raman bands in the spectral region of 354 /597 suppose that the phase called ‘paratacamite’ by cm 1, as well as by a band at 293 cm 1 being Guineau is in fact ‘clinoatacamite’. However, his attributed to the M /Cl stretching vibration. Raman spectrum (980, 918, 850, 827, 516 cm 1) being rather old (hence with an uncertain calibra- 4.6.2. F22*/Matlockite, PbClF, tetragonal, P/4// tion) and of very weak spectral resolution, the nmm differences in wavenumber position cannot really Raman bands (wavenumbers): 238, 227, 163; be considered as significant. 1 155, 132, 105, 84 cm . Bell et al. [6] attribute the following Raman bands to atacamite: 974, 911, 846, 821, 513, 360 1 4.6.3. F23*/Cotunnite, PbCl2, orthorhombic, cm . These results almost perfectly fit our Pnam spectra of atacamite (type A in the figure), whereas Raman bands (wavenumbers): 202, 169, 158 those of Guineau are all substantially higher in cm 1. wavenumber. 2264 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
The spectrum of clinoatacamite (type B in the 4.7. Carbonates and hydroxy-carbonates figure) is quite different. Both atacamite and clinoatacamite occur in the powder determined 4.7.1. F33*/Cerussite, PbCO3, orthorhombic, by XRD. Pmcn, £ None of the spectra in the literature concerning Raman bands (wavenumbers): 1477, 1370, 1052; 1 Cu2Cl(OH)3 give as many Raman bands as those 246, 225, 176, 152 cm . of type A and B here. Weak bands around 412, 450 These bands correspond perfectly to the obser- and 590 cm 1 do not seem to be listed anywhere vations made in a study dedicated to the identifi- but they occur in the all our spectra of type A and cation of various oxy-hydroxy-carbonates of lead B; their allocation is not yet resolved. by RM [34].
4.6.7. F27*/Botallackite, Cu2Cl(OH)3, 4.7.2. F34*/Smithsonite, ZnCO3, trigonal, R/3/c, £ monoclinic, P/21//m, £ Raman bands (wavenumbers): 1734, 1404, 1089; Raman bands (wavenumbers): 3504, 3420, 897, 731, 301, 192 cm 1. 857, 678*, 503, 450; 401; 324, 279, 251, 175, 155, Griffith [3] gives for this mineral the following 115 cm 1. Raman bands: 1412, 1093, 733, 140 cm 1. The three polymorphs (atacamite, clinoataca- mite and botallackite) are easily distinguishable by 4.7.3. F35*/Azurite, Cu3(CO3)2(OH)2, 1 their spectra in the 100 /1000 cm range, but also monoclinic, P/21//a, (£ /two minor unidentified XRD 1 in the 3100 /3700 cm range. The fourth poly- bands) morph paratacamite does not exist without small Raman bands (wavenumbers): 3423, 1578, 1458, amounts of zinc [11]. 1424, 1295, 1098, 938, 839, 764, 739, 543, 402; 334, 283, 267*,249, 240*,177, 155, 139 cm 1.
4.6.8. F28*/Calumetite, Cu(OH,Cl)2 ×/ 2H2O, There are some differences between the pre- orthorhombic, unknown sented Raman spectra and those listed in the Raman bands (wavenumbers): 3550, 3450, 1054, literature [6,35]: extra bands at 155, 240, 267, 1041; 985, 843, 622, 595, 489, 451, 409, 347, 314, 739, 1295 cm 1 in our sample which may be 259, 236, 193, 184, 164, 145, 139, 128 cm 1. imputed to non-identified species existing in addi- tion to azurite. Other bands correspond perfectly
4.6.9. F29*/Cumengite, Cu20Pb21Cl42(OH)40, to the data presented by McCann et al. [35] (1576, tetragonal, I/4//mmm 1429, 1368, 1095, 932, 838, 763, 669, 552, 463, 398, Raman bands (wavenumbers): 683, 498*, 459*, 248 cm 1) and Bell et al. [6] (1580, 1459, 1432, 255*, 197*, 152; 130 cm 1. 1098, 940, 839, 767, 746, 545, 403, 335, 284, 250, 180, 145 cm 1).
4.6.10. F30*/Boleite, Ag9Cu24Pb26Cl62(OH)48, tetragonal, Pm/3/m 4.7.4. F36*/Malachite, Cu2CO3(OH)2, Raman bands (wavenumbers): 3406, 925*, 823*, monoclinic, P/21//a, (£ /three minor unidentified 703, 487*, 462, 357*, 298*, 221; 161, 151 cm 1. XRD bands) Raman bands (wavenumbers): 3378, 3308, 1493,
4.6.11. F31*/Fiedlerite, Pb3Cl4(OH)2, triclinic, P/ 1462, 1367, 1100, 1067, 753, 721, (512(L), 538, 1 3/ 597(L), 434; 355, 270, 219, 180; 154 cm (L /
Raman bands (wavenumbers): /737, 600, 331; linarite). 272; 133 cm 1. The Raman spectrum of malachite is well- known since a long time ago. Nevertheless, there
4.6.12. F32*/Laurionite, PbCl(OH), are some differences in the spectra listed in orthorhombic, Pnam literature, e.g. 1498, 1372, 1104, 1064, 757, 724, Raman bands (wavenumbers): 1425, 1377; 1055, 604(L), 540, 516, 437, 355, 274, 225 cm 1 [4]; 840, 683, 217*,176, 150 cm 1. 1094, 1058, 753, 722, 538, 436, 355, 270, 220, 180, M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266 2265
155, 118 cm 1 [5]; 1492, 1085, 1051, 757, 558, 553, In the same way, the band at 1052 cm 1 is 509(L), 433, 354, 268, 217, 178, 155 cm 1 [6]. rather intense and cannot serve at the moment for Whereas most of the characteristic Raman discriminating between cerussite, hydrocerussite bands of malachite are correctly reproduced by and plumbonacrite as it is indeed present in the the three authors referenced above and by our own Raman spectra of all three mineral species with 1 data, one can, however, observe in some of these slight variations in wavenumber (9/1 /2cm ). spectra bands belonging to another mineral spe- Brooker et al. [3] listed a large number of bands for cies. This is notably the case of the mixed Pb and hydrocerussite (3533, 1735, 1645, 1395, 1363, 1052; Cu hydroxy-sulphate linarite (L) (see F16) which is 1049, 1028, 865, 770, 705, 695, 681, 415, 325, 126, tentatively identified here thanks to its two char- 106, 74, 49 cm 1). acteristic Raman bands at 512 and 597 cm 1 (in From all these results, it seems that our two our spectrum). The co-existence of linarite and samples are both constituted of a mixture of malachite in various other natural samples of the hydrocerussite with probable plumbonacrite and Gallery of Mineralogy consolidates this hypoth- cerussite. esis. Nevertheless, the presence of linarite in this sample of malachite was not confirmed by the 4.7.6. F38*/Aurichalcite,
XRD analysis, whereas the presence of three (Zn,Cu)5(CO3)2(OH)6, trigonal, P/21//m, £ supplementary peaks in the XRD spectrum of Raman bands (wavenumbers): /3331, 1511, the malachite were not assignable such that all is 1479, 1074; 843, 750, 734, 709, 503, 463, 437*, 389, not yet clear here. 354*, 234, 211, 175, 141 cm 1. The band at 118 cm 1 [5] cited above, and also The band around 3331 cm 1 is noticeably wide. observed in a certain number of our own samples, probably results from a parasite from the 514.5 nm 4.7.7. F39*/Rosasite, (Zn,Cu)2CO3(OH)2, 1 Ar laser. Bands at 3308 and 3378 cm corre- monoclinic, P/21//a, £ sponding to the OH bonds in malachite, as well as Raman bands (wavenumbers): 3470, 3422*, band at 1462 cm 1, were not listed by any of the 3232, 1540, 1514, 1453, 1086; 1060, 843, 833*, authors mentioned above. 702, 508, 482*,409, 390*, 332, 308*, 231, 208*, 193; 146; 126 cm 1.
4.7.5. F37*/Hydrocerussite, Pb3(CO3)2(OH)2, 4.7.8. F40*/Hydrozincite, Zn5(CO3)2(OH)6, unknown, £ monoclinic, C/2//m, £ Raman bands (wavenumbers): 3534, 1371, 1052; Raman bands (wavenumbers): 1544, 1371, 1061; 421, 321 cm 1. 732, 704, 389, 340*, 230, 152; 139, 121, 81 cm 1. Two samples of minerals labelled ‘hydrocerus- site’ were analysed by XRD and by RM and both 4.8. Hydroxy-silicates presented very similar results. The Raman bands attributable to hydrocerussite exclusively are at 4.8.1. F41*/Dioptase, CuSiO3 ×/ H2O, trigonal, R/ 321 and 3534 cm 1. Hydrocerussite is thus present 3; £ in these samples (confirmed by XRD analysis), Raman bands (wavenumbers): 3371, 1025, 1006; while other phases also seem to exist. 960, 916, 743, 660; 525, 452, 431, 400, 357; 325, Plumbonacrite, for example, could be charac- 294, 265, 240*, 225, 161, 140, 133 cm 1. terised by its Raman band at 420 cm 1 (P), but the band at 1371 cm 1 is too weak in intensity to be 4.9. Mixed phases sure of its wavenumber and thus cannot be definitely attributed to plumbonacrite (1385 4.9.1. F42*/Connellite, Cu19Cl4SO4(OH)32 ×/ 1 1 cm ) [8]. It fits cerussite (1370 cm ) (see above: 3H2O, hexagonal, P/62c¯; £ F33), but hydrocerussite has a band at /1363 Raman bands (wavenumbers): 984; 403; 254*, cm 1 [34]. 130 cm 1. 2266 M. Bouchard, D.C. Smith / Spectrochimica Acta Part A 59 (2003) 2247 /2266
[10] D.C. Smith, in: F. Rull, D.C. Smith, H.G.M. Edwards 4.9.2. F43*/Buttgenbachite, (Eds.), Georaman and Archaeoraman, University Valla- Cu18(NO3)2(OH)32Cl3 ×/ H2O, hexagonal, P/6 // 3 dolid Press, Valladolid, Spain, 2003 (in preparation). mmc [11] J. Jambor, J. Dutrizac, A. Roberts, Can. Mineral. 34 Raman bands (wavenumbers): 1054, 1041, 985, (1996) 61. 843, 622, 595, 489, 451, 409; 347, 314, 259, 236, [12] M.E. Andersen, Microbeam Anal. (1982) 197. 193, 184, 164, 145; 128 cm 1. [13] M.P. Alonso, K. Castro, M.D. Rodrı´guez, M.Olazabal, J.M. Madariaga, in: ‘‘ART 2002’’, Seventh International Conference on Non-destructive Testing and Microanalysis 4.9.3. F44*/Phosgenite, Pb CO Cl tetragonal, P/ 2 3 2, for the Diagnostics and Conservation of the Cultural and 4//mbm, £ Environmental Heritage, University of Antwerp, June Raman bands (wavenumbers): 1063; 668, 281, 2002, Abstract vol., p. 217. 252, 181*, 154, 129, 87; 81, 53, 47 cm 1. [14] M. Pastoureau, La couleur et l’historien, in Pigments et colorants, Ed. CNRS, Paris, 1990, p. 21. [15] E. Wolska, U. Schwertmann, N. J Miner, M.H. 5 (1993) 4.9.4. F45*/Pyromorphite, Pb5(PO4)3Cl, 213. hexagonal, P/6 //m, £ 3 [16] G.A. Waychunas, D.H. Lindsley, Rev. Mineral. 25 (1991) Raman bands (wavenumbers): 814; 789, 769, 11. 1 410*, 340, 313, 177 cm . [17] P. Pascal, Nouveau Traite´ de Chimie Mine´rale, Tome VIII, Masson & Cie, Paris, 1963. [18] L. Bussotti, M. Pia-Carboncini, E. Castellucci, P.-A. Acknowledgements Mando, Stud. Conserv. 42 (1995) 83. [19] J. Xu, W. Ji, X.B. Wang, H. Shu, J. Raman Spectrosc. 29 (1998) 613. Henri-Jean Schubnel, Jacques Skrok, Benjamin [20] N. Phillips, Doctoral thesis, Jussieu, Paris VI, Paris, 1993, Rondeau, Constantin Carabatos-Nedelec and p. 210. Herve´De´bitus are all thanked for their kind [21] E.H. Nickel, M.C. Nichols, Mineral Reference Manual, cooperation in the search for samples and their Van Nostrand Reinhold, New York, 1991. [22] M.C. Bernard, A. Hugot-le-Goff, B. Vu-Thi, J. Electro- loan. chem. Soc. 140 (11) (1993) 3065. [23] D.C. Smith, M.A. Bouchard, M. Lorblanchet, J. Raman Spectrosc. 30 (1999) 347. References [24] D.L.A. de-Faria, S.V. Silva, M.T.D. Oliveira, J. Raman Spectrosc. 28 (1997) 873. [1] D.C. Smith, H.G.M. Edwards, in: A. Heyns (Ed.), [25] C. Johnston, Vibrational Spectrosc. 44 (1) (1990) 87. Proceedings ICORS-98, XVIth International Conference [26] G.N. Kustova, E.B. Burgina, S.G. Poryvaev, V.A. Sady- kov, Phys. Chem. Miner. 18 (1992) 379. on Raman Spectroscopy, Cape Town, 6 /11 September, Wiley, Chichester, 1998, p. 510. [27] R.J. Thibeau, C.S. Brown, R.H. Heidersbach, Appl. [2] D.C. Smith, Mineral. Soc. Bull., Mineral. Soc. Great Spectrosc. 32 (1978) 532. Britain (1999) 3. [28] K.P.J. Williams, I.C. Wilcock, I.P. Hayward, Spectroscopy [3] W.P. Griffith, in: R.J.H. Clark, R.E. Hester (Eds.), (Eugene Oreg.) 11 (3) (1996) 45. Spectroscopy of Inorganic-Based Materials, Wiley, New [29] M. Bouchard, Me´moire de DEA, IPH, Muse´um National York, 1987, p. 119. d’Histoire Naturelle, Paris, 1998, p. 66. [4] B. Guineau, Spectrochim. Acta A 53 (1987) 2159. [30] A. Clark, Heys Mineral Index: Mineral Species, Varieties [5] M. Pinet, D.C. Smith, B. Lasnier, La Microsonde Raman and Synonyms, third ed, Chapman & Hall, London, 1993. en Gemmologie, Revue de Gemmologie, AFM, Paris, [31] M. Schmidt, H.D. Lutz, Phys. Chem. Miner. 20 (1993) 27. 1992, p. 11 (Chapter II; number spe´cial hors se´rie). [32] A. Derbyshire, R. Withnall, J. Raman Spectrosc. 30 (1999) [6] I.M. Bell, R.J.H. Clark, P.J. Gibbs, Spectrochim. Acta A 185. 53 (1997) 2159. [33] N.B. Colthup, L.H. Daly, S.E. Wiberley, Introduction to [7] L. Burgio, R.J.H. Clark, Spectrochim. Acta A 57 (2001) Infrared and Raman Spectroscopy, Academic Press, 1491. London, 1964, p. 511. [8] M. Bouchard-Abouchacra, Doctoral thesis, Muse´um Na- [34] M.H. Brooker, S. Sunder, P. Taylor, Can. J. Chem. 61 tional d’Histoire Naturelle, Paris, 5 De´cembre 2001, p. 360. (1983) 494. [9] D.C. Smith, Georaman-96, Terra Nova 8, Terra Abstracts, [35] L.I. McCann, K. Trentelman, T. Possley, B. Golding, J. 1996, p. 23 (Abstract supplement number 2). Raman Spectrosc. 30 (1999) 121.