Mineralogical Magazine, August 1998, Vol. 62(4), pp. 451–459 Crystal structureof macphersonite (Pb4SO4(CO3)2(OH)2):comparison withleadhillite 1 1,2,3 4,5 IAN M. STEELE , JOSEPH J. PLUTH AND ALEC LIVINGSTONE 1 Department of Geophysical Sciences, 2 Consortium for Advanced Radiation Sources, 3 Materials Research Science and Engineering Center, The University of Chicago, Chicago IL60637, USA 4 Department of Geology, The Royal Museum of Scotland, Chambers St., Edinburgh EH11JF, UK ABSTRACT Thecrystal structure of macphersonite (Pb 4SO4(CO3)2(OH)2, Pcab, a = 9.242(2), b =23.050(5), c = 10.383(2) AÊ )fromLeadhills, Scotland has been determined to an R =0.053.The structure has many featuresin common with its polymorph leadhillite including three distinct types of layers. Layer A includessulphate tetrahedra, Layer B iscomposed of Pb and OH, whileLayer C iscomposed of Pb and CO3 withtopology identical to that in cerussite. In both macphersonite and leadhillite these layers are stackedalong [010] as ...BABCCBABCC... Thedouble CC layeris almost identical in the two structuresand forms a structuralbackbone and occurs in other structures including hydrocerussite and plumbonacrite.The sulphate layer shows the greatest difference between the two structures and can be describedby a patternof up or down pointing tetrahedra. For macphersonite the sequence along [001] is...UDUDUD ...while in leadhillite the sequence along [010] is ... UDDUUDDU... Thislatter sequence effectivelydoubles b relativeto the equivalent direction in macphersonite. Susannite, a third polymorph,may have yet another sequence of sulphates to give trigonal symmetry; by heating leadhillite,displacive movements of sulphate groups may occur with a conversionto susannite. KEY WORDS: macphersonite,leadhillite, susannite, cerussite, hydrocerussite, carbonate, sulphate. Introduction Macphersoniteis the rarest of the three poly- morphs,only two composite crystals being known MACPHERSONITE (Livingstoneand Sarp, 1984) is onseparat especimensfrom the Leadhil ls- trimorphouswith leadhillite and susannite with Wanlockheadorefield. Parallel oxidatio nof thecomposition Pb 4SO4(CO3)2(OH)2. All are otherprimary sulphides of Cu and Zn lead to foundin the classic Leadhills region of southwest mixedmetal species of carbonates,sulphates and Scotlandand represent a smallfraction of the hydroxides. some60 minerals identified from this region Previousstudies of the these trimorphs have (Temple,1956) .Fromprimary galena, oxidation establishedtheir compositional identity and close productsincludeanglesi teand cerussit eor relationshipsamong their unit cell geometries hydrocerussite.These oxidized products lead to (LivingstoneandSarp, 1984). They can be awealthof minerals which include sulphates, distinguishedby differen cesin their X-ray carbonates,hydroxides, or mixtures thereof which patterns,albeit subtle differences in the case of includethe trimorphou sgroupabove; other susanniteand leadhillite (Livingstone and Russell, phasesaregiveninTemple(1956). 1985),or by their infrared absorption spectra (Russell et al.,1984).Thepolymorphs can also be distinguishedby their thermal behaviour (A.L. , 5 unpublisheddata). The structure of leadhillitewas Present address: 6St. Ronan ’sTerrace, Innerleithen, describedby Giuseppetti et al.(1990)in which a Peeblesshire EH44 6RB, Scotland doublelead carbonate layer, nearly identical to # 1998The Mineralogical Society I. M. STEELE ETAL. layersin cerussite, anchors a structurewhich (1984).Sufficientmaterial (NMS G1991-31-21) includesPbSO 4 and Pb(OH)2 layers.The dimen- wasavailable to selecta samplefor single crystal sionalsimila ritiesbetwee nleadhillitea nd studiesbut the common twinning made it difficult macphersoniteindicate that the latter has a toobtain a singlecrystal. Multiple crystals could similarstructure and our main objectives are to usuallybe recognized optically, but only after determinethe macphersonite structure and then to confirmationwith routine precession photographs comparewith leadhillite and possibly suggest wasa sample,free of twinning, obtained. variationsfor the susannite structure. Thesample selected for single crystal data Whilethese objectives are primarily crystal- collectionwas a cleavageplate with dimensions lographic,it should be pointed out that the lead giveninTa ble1.Pre cessionp hotographs carbonates,sulphatesand hydroxides play a confirmedthe space group as Pcab with a cell significantrole in thelead acid battery chemistry. of a = 9.24, b = 23.0, c = 10.4 AÊ ,consistentwith Structuralderivatives where sulphate or hydro- datareported by Livingstone and Sarp (1984). xidegroups replace Pb in either the tetragonal Diffractionswere sharp with no indication of (litharge)or orthorhombic (massicot) PbO struc- multiplec rystalsortwinn ing.The c rystal turescomprise intermediate lead sulphates in the (completedetails in Table 1) was mounted on productionof lead acid batteries (Steele et al., anautomated Picker-Kris el4-circle diffract- 1997;Steele and Pluth, 1998) .Detrimentalto lead ometer with b offset 18 from the f axis. acidbatteries is the formation of lead carbonate- Refinementusing 23 diffractions (17 < 2 y < hydroxidesincluding hydrocerussite and plumbo- 348: l = 0.71073 AÊ ),eachthe average of nacrite.The mechanism of formation of these automaticcentring of 8 equivalentsettings gave phasesis not well known, but their presence in thefinal cell parameters (Table 1) consistentwith batteryplates reduces acid permeability within the PbO2 networkand increases the resistivity of the electrolyte(Vinal, 1955). While these two phases TABLE 1.Experimental details and crystallographic commonlyoccur, one may expect other phases datafor macphersonite includinglead carbonate -sulphate-hydroxides, possiblymacphersonite and/ orleadhillite, may alsoform within lead acid batteries. Natural (A) Crystal-cell data occurrencesof lead silicate-carbonate -sulphate- a (AÊ ) 9.242(2) hydroxideshave been documented, e.g. kegelite b (AÊ ) 23.050(5) Ê (Dunn et al.,1990),mattheddleite (Livingstone et c (A) 10.383(2) Ê 3 al.,1987),and an unnamedphase (Cipriani et al., V (A ) 2211.9(8) Space group Pcab 1995),and given that silica within a leadacid Z 8 batteryis extremely detrimental, one can spec- Formula Pb4SO4(CO3)2(OH)2 ulatethat these or similar compounds form and ­ 3 Dcalc (g cm ) 6.480 effectivelypreven tnormale lectrochemical m (mm ­ 1) 60.96 reactions. Fromboth an academic and industrial point of (B) Intensity measurements view,the description of the lead compounds of Crystal size 80 6 55 6 25 mm carbonate,sulphate and hydroxide may prove Diffractometer Picker, Krisel control usefulfor interpreting both natural and synthetic Monochromator Graphite chemicalsystems. The natural occurrences of Radiation MoK minerals,such as described here, offer advantages Scan type o becauseproducts are available of sufficient size 2y range 3.5 ­ 55.0 Diffractions measured 10,206 foraccura tedo cumentationincontra stto Unique diffractions 2,556 industrialoccurrenc eswhich are notorious ly fine-grained. (C) Refinement of the structure R 0.053 R = S(||Fo|-|Fc||)/S|Fo| Rw 0.121 Rw = Experimentaldetai ls andstructure solution 2 2 2 2 2 Ý [Sw(|F0|-|Fc|) /Sw|F0| ] Theoccurrence of macphersonite,its relationships Variable parameters 173 toothercoexisting lead phases, and its properties ‘Goodness of fit ’ (GOF) 1.1 havebeen described by Livingstone and Sarp 452 CRYSTAL STRUCTURE OFMACPHERSONITE 2 2 ­ 2 2 theprecession study. A totalof 10,206 intensities totalcounts) ], w = (sF) ,R(F) =0.053,R w(F ) werecollected with o stepscans, 0.02 8 steps, 1 =0.121,S =1.09;largest shift/ e.s.d.~0.002 for all sec/step,and a scanwidth 1.0 8 for a 2y range of parameters;maximum and minimum heights on 3.5­ 558.Mergingyielded 2,556 intensities (R int = finaldiffer ence-Fouriermapare+6. 4and 0.063),all of which were used in refinements: ­ 5.1 eAÊ ­ 3;computerprogra ms:local data datacollection range h + 12, k = 0 to 30, l + 13; reduction,SHELXTL TM.Finalatomic coordi- meanintensity variation of 3standarddiffractions natesand isotropic displacement parameters are = 6%.Ananalytical absorption correction was givenin Table 2, anisotropic displacement para- appliedto the data using the m valueand crystal metersin Table 3, and interatomic distances in dimensionsin Table 1. Systemati cabsences Table 4. indicatedspace group Pcab consistentwith the precessionstudy. The initial model was derived fromthedirectmethodsprogrammein Discussionof structure SHELXTLTM (Trademarkof Siemens Energy Themacphersonite structure can be best repre- andAutomation,Inc.,Analytical sentedas a sequenceof three types of layers Instrumentation,Madison, WI, USA). AllPb stackedalong [010] .LayerA iscomposed of atomswere included in a leastsquares refinement sulphatetetrahedra, Layer B ofleadand OH, and usinganisotropic temperature factors, and the S, LayerC oflead and carbonate. The stacking O,andC positionswere located in subsequent sequenceis illustratedwith a projectionparallel to difference-Fouriermaps and included in the [100]inFig. 1 andcanb edescribedas refinement. ...BABCCBABCC... stacking.These same layers Inthe final model, 173 variables were refined: willbe shown later to occur in the leadhillite scalefactor, extinction parameter, positions for 19 structurein which the same stacking sequence atoms,and anisotrop icdisplaceme ntfactors. occurs.Each layer is illustrated in plan view in Neutralscatteri ngfactors found internal to Fig. 2a, b and c. SHELXTL wereused. The final least-squares LayerA, composedof sulphate groups