Raman Spectroscopy of the Minerals Boleite, Cumengeite, Diaboleite And
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Mineralogical Magazine, February 2003, Vol. 67(1), pp. 103–111 Raman spectroscopyof the mineralsbo le¨ite,cumenge¨ite, diabole¨ iteandphosgenite – implications forthe analysisof cosmetics of antiquity 1, 2 1 R. L. FROST *, P. A. WILLIAMS AND W. MARTENS 1 Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, GPOBox 2434, Brisbane, Queensland 4001, Australia 2 Centre for Industrial and Process Mineralogy, School of Science, Food and Horticulture, University of Western Sydney, Locked Bag 1797, Penrith South DC,NSW 1797, Australia ABSTRACT Theapplication of Raman spectroscopy to the study of the mixed cationic Pb-Cu and Pb-Cu-Ag minerals:bole ´ite,cumenge ´iteand diabole ´itehas enabled their molecular structures to be compared. Eachof these three minerals shows different hydroxyl-stretchin gvibrationalpatterns, but some similarityexists in the Raman spectra of thehydroxyl-deformatio nmodes.The low-wavenumber region ischaracterized by the bands assigned to the cation-chloride stretching and bending modes. Phosgenite isalso a mixedchloride-carbonate mineral and a comparisonis made with the molecular structure of theaforementioned minerals. Raman spectroscopy lends itself to thestudy of these types of mineralsin complexmineral systems of secondary mineral formation. KEY WORDS: bole´ite,cumenge ´ite,diabole ´ite,lead, chloride, phosgenite, Raman spectroscopy. Introduction authorssuch as Dioscorid esand Pline (1st CenturyB.C.): silver foam PbO iscrushed and INTEREST inthecompounds of Pb for pharmaceu- mixedwith rock salt and sometimes with natron ticaland cosmetic purposes of antiquity has been (Na2CO3)(Tsoucaris et al.,2001).It followsthat knownfor some considerable time (Lacroix, theEgyptians mastered this kind of chemical 1911;Lacroix and de Schulten, 1908). Indeed synthesisand technology very early, a factof recentchemical analyses have shown that the Pb greatimportance in the history of sciences. Fire- mineralssuch as crushed ore of galena (PbS) and basedtechnology was employed to manufacture cerussite(Pb CO 3)togetherwith lau rionite EgyptianBlue pigments in the third millennium (PbOHCl)and phosgenite (Pb 2Cl2CO3) were B.C. Itis now suggested that wet chemistry was usedas cosmetics in Egyptian times (Martinetto alreadyin existence some 4000 years ago. et al.,2001;Tsoucaris et al.,2001;Walter, 1999). Someof theseminerals also formed the basis of Itmust be noted that the latter two minerals are manypaint pigments (Bersani et al.,2001;Black rarein nature and therefore it isinferred that such andAllen, 1999; Brooker et al.,1983;Burgio et al., mineralswere synthesized. Ancient literature has 2001;Burgio et al.,1999;Burgio et al., 2000). providedinformati onon the pharmace utical Manyof these pigments were based upon lead preparationsof these minerals (Walter, 1999; dioxide(PbO 2).The Raman spectra of plattnerite Walter et al.,1999).Support for this statement [lead(IV)oxide, PbO 2]andof the lead pigments red comesfrom recipes of medicinal products to be lead (Pb3O4),lead monoxide [PbO, litharge ``usedin ophthalmol. ’’ reportedby Greco-Roman (tetragonal)and massicot (orthorhombic)], lead white[basic lead carbonate, 2PbCO 3.Pb(OH)2] *E-mail: [email protected] andof their laser-induced degradation products DOI: 10.1180/0026461036710088 havebeen measured. The degradation of PbO 2 has # 2003The Mineralogical Society R. L. FROSTETAL. beenshown to follow the pathway PbO 2 ? Pb3O4 smartendurance single bounce diamond ATR ? PbO (litharge) ? PbO (massicot);the shorter cell.Spectra over the 4000 to 525 cm –1 range thewavelength of the excitation line, the greater its wereobtained by the co-addition of 64scanswith –1 power.The Raman spectrum of PbO 2 showedthree aresolutionof 4 cm anda mirrorvelocity of bands,at 653, 515 and 424 cm – 1,identied as 0.6329cm/ s. arisingfrom the B2g, A1g and Eg modesrespec- Spectroscopicmanipulation such as baseline tively,by analogy with the corresponding modes of adjustment,smoothing and normalization were – 1 isostructuralSnO 2 (776,634 and 475 cm ). What performedusing the Spectracalc software package isof particular importance is that the synthetic GRAMS (GalacticIndustries Corporation, New mineralssuch as laurionite and phosgenite, which Hampshire,USA). Bandcomponent analysis was wereused by the ancient Egyptians, have not been undertakenusing the Jandel ‘ Peakt’ software analysedby Raman spectroscopy. In fact few package,whichenabled the type of tting Ramanor infrared (IR) spectra of these two functionto be selected and allows speci c mineralshave been forthcoming. parametersto be xedor varied accordingly. Band ttingwas done using a Gauss-Lorentz cross-productfunction with the minimum number Experimental ofcomponent bands used for the ttingprocess. Minerals TheGauss-Lorentz ratio was maintained at values Theminerals used in thisstudy were supplied by >0.7and ttingwas undertaken until reproducible theAustralian Museum (ASM). The minerals resultswere obtained with squared correlations of havebeen characterized by bothX-ray diffraction r2 >0.995. (XRD) andby chemical analysis using ICP-AES techniques. Thefollowing samples were used: (a) sample Results anddiscuss ion ASM-D49056bole ´itefrom the Amelia Mine, Phosgeniteis an example of a mixedhalogen- SantaRosalia, Baja, California, Mexico; (b) carbonatespecies of formula (Pb 2CO3Cl2). This sampleASM-D 27575cumenge ´iteBeleo, Baja mineralis compositionally related to northupite, California,Mexico; (c) sample ASM D36845 parisiteand bastna ¨sitebut is structurally different, diabole´itefrom Mannoth mine, Tiger, Arizona, belongingto space group P4/mbm and factor USA; and(d) sample ASM D191881phosgenite group D4h.Thecarbonate ion lies on C2v sites and fromConsols mine, Broken Hill, South Australia. thisresults in considerablesymmetry reduction as maybe evidencedby thesplitting of the n3 and n4 bands.The mineral, which is in some ways Ramanm icroprobespectroscop y compositionallyrelated,isdiabole´ite Crystalsofthe minera lswere place dand (Pb2CuCl2(OH)4)(Abdul-Samad et al., 1981). In orientatedon a polishedmetal surface on the thismineral, stoichiometrically the carbonate has stageof anOlympusBHSM microscope,which is beenreplaced by hydroxyl units. This is a mixed equippedwith 10 6 and 506 objectives.The anionicand a mixedcationic species. The crystal microscopeis part of a Renishaw1000 Raman structureof diabole ´ite,Pb 2Cu(OH)4Cl2, is tetra- microscopesystem,which also includ esa gonal, P4mm, a = 5.880(1), c = 5.500(2) AÊ , V = monochromator,a ltersystem and a Charge 190.1 (1) AÊ 3, Z =1(Cooperand Hawthorne, CoupledDevice (CCD). Ramanspectra were 1995).There is one unique Cu 2+ position excitedby a Spectra-Physicsmodel 127 He-Ne coordinatedby four (OH – ) and two Cl – anions; laser(633 nm) at a resolutionof 2 cm – 1 in the the Cl – anionsoccupy the apical positions, and rangebetween 100 and 4000 cm – 1. Repeated theCu octahedron shows the [4+2] distortion acquisitionusing the highest magni cation was typicalof Cu 2+ oxidesand oxysalts. There is one accumulatedto improve the signal to noise ratio unique Pb2+ positioncoordinated by four (OH –) inthe spectra. Spectra were calibrated using the and four Cl – anions.All the OH – unitsform short 520.5 cm –1 lineof a siliconwafer. (0.246nm) bonds with Pb 2+,andlie to oneside of thecation, whereas the Cl – anionsall form long (0.322and 0.340 nm) bonds with Pb 2+, and are on IRspectroscop y theother side of the cation. Pb 2+ shows a one- Infrared(IR) spectra were obtained using a sidedcoordination typical of stereoactive lone- NicoletNexus 870 FTIR spectrometerwith a pairbehavio ur.There are two unique Cl – 104 PB-CU-AG MINERALSAND ANCIENTCOSMETICS positions;one isstronglybonded to Cu 2+ and Pb2+ regularbiaugmented trigonal prism. There are two cations,whereas the other is primarily held in Cusites. The coordina tionpolyhedr ashare placeby a networkof hydrogenbonds emanating elementsto form prominent columns or rods of from the (OH – )groups.The Cu octahedra form polyhedraparallel to the c axisand centred on the corner-sharingchains along the c axis,and these 4-foldaxes of the unit cell. chainsare cross-linked by Pb 2+ cationsand by hydrogenbonding. Hydroxyl-stretchingbands Bole´iteoriginall ywrittenas Pb 26Ag9Cu24 Cl62(OH)47.H2Ohasbee nfoundto be of TheRaman spectra of the four minerals: (a) formula KPb26Ag9Cu24Cl62(OH)48 (Cooper and phosgenite,(b) bole ´ite,(c) diabole ´iteand (d) Hawthorne2000). The crysta lstructureis cumenge´itein the 3200 to 3700 cm –1 region are distortedcubic (Gossner, 1928; Gossner, 1930; shownin Fig. 1. The result softhe band Rouse,1973).Potass iumwasde tectedby componentanalysis of the separate regions are electron-microprobeanalysis, but the amount reportedin Table 1. Of coursephosg enite determinedwas only 50% of the amount indicated containsnowater or hydroxy lgroupsand bysite-sc atteringrenement. However ,the Ramanspectroscopy clearly shows the absence renement results show K tobe disordered ofany hydroxyl- stretchingvibrations.X-ray withina largecage in the structure, and the crystallographycombined with the application electron-beambombardment probably induces ofIR spectroscopyto show the presence/ absence rapidmigration of K withinthe structure. The ofwater molecules, indicates that no water IRspectroscopyshowed that there is no H 2O moleculesare present in the formulae of bole ´ite, presentin the structure (Cooper and Hawthorne, diabole´iteand cumenge ´ite.Only hydroxyl units 2000).In some ways cumenge ´iteis composition- arepresent. For bole ´ite,three