American Mineralogist, Volume61, pages l00l-1004, 1976

Strontianitecomposition and physical properties

J.Alexennen SpeeR AND MARGAneT L. HeNsLsv-DUNN' Departmentof GeologicalSciences Virginia PolytechnicInstitute and State Uniuersity Blacksburg,Virginia 2406I

Abstract

Microprobeanalyses indicate that strontianitesfrom 12 localitieslie essentiallyalong the CaCOs-SrCO,join betweenSro.r.sCa6.o2, and Sro,urCao.r' with Ba and Pb presentat the 2500-3600ppm and the 100-600ppm levelsrespectively. Lattice parametersvary regularly acrossthe join , with d{srgivingthe bestindirect measurement of SrCOscontent: mole percent SrCOa(40.95) : -2116.24+ 1162.84(d,r, A). Densitiesrange from 3.78for SrCO'to 3.59 for SroTusCao.2naCOs, with values in excessof 3.78 indicatingthat the Ba-Pb contentsare presentin morethan trivial amounts.Abundant submicroscopic twinning precluded measure' ment of optical properties.

Introduction the standardsand unknownsare of similar composi- be accurateto about 2 per- An interestin the strontianiteoccurrences in the tions, Sr and Ca should present.No problemwas encoun- lower Paleozoiccarbonate rocks of the Appalachian centof the amount Ba and Pb, althoughtheir Mountains revealedthe needfor a simplemethod of teredin the detectionof is probablymuch higher because of the compositionaldetermination. While there are several relativeerror and problems in estimatingthe studiesdealing with physicalproperties of synthetic counting statistics listedin TableI strontianites(Holland et al., 1963:Froese and Wink- bacrgrounds.The numberof cations places preventround-off ler,1966;and Chang,1965, l97l), no work hasbeen are givento four decimal to doneto testtheir applicabilityto naturalmaterial. In errorsin the calculations. from packed the presentstudy we have examinedthe range of Unit cell parameterswere determined powdered using spinel(a = chemicalvariation of l2 strontianitesand the rela- mounts of strontianite, Thesewere run on tionshipsbetween chemical composition and some 8.0833A) asan internalstandard. physicalproperties. a Norelco diffractometerat 0.25o 20/min, using monochromatizedCuKo radiation. Each sample was Experimentalprocedures scannedat leastonce with increasingand decreasing peak The samplesexamined in this study are listed in 20. All peaks were measuredat two-thirds to the data of Table 1.Other data from the literatureused in estab- height and indexed with reference (1954). programof lishingthe determinativecurves are from Swansone/ Swansonet al. The least-squares (1973)was used to refinethe al. (1954), Holland et al. (1963), and De Villiers Applemanand Evans placeswere retained (1971).The 12 strontianiteslisted in Table I were latticeparameters. Four decimal preventround-off errors in the analyzedwith an ARL electronmicroprobe, using on the cell edgesto the Eupeon VII computerprogram (Rucklidge and calculations. with the useof a Ber- Gasparrini,1969) for datareduction. Standards used Densitieswere determined correctedfor for the elementswere syntheticSrCO' (Sr), calcite man torsion balance,using toluene, The densities (Ca),witherite (Ba), and cerussite(Pb). Carbon was temperature,as a displacementliquid. determinations obtainedby calculatingthe numberof carbonatoms of Table I are averagesof several piecesper sample.As accordinsto the relationC : Sr t Ca * Ba * Pb.As made on two to four different mostof the strontianitesoccur as tufts of smallacicu- t Presentaddress: 3880 Sardis Road, Murrysville,Pennsylvania lar crystals,care was taken that air did not remain I 5668. trappedbetween the fine crystals.

l00l 1002 J. A. SPEERAND M. L. HENSLEY.DUNN

Tnslr l Crystaland chemicaldata for strontianites

L3

Sr0 60.17 58.33 64.75 56.20 67 52 60.19 56.39 63.78 61.63 68.14 64.15 s7.39 7(L9 Cao 7,26 8. 12 3.36 9.8s 6.34 7.r3 9.08 4.20 6.11 1.09 Pbo 0.05 0.03 0.09 0,04 o.o4 0.01 0.03 0.02 0.04 0.08 0.09 0.07 BaO 0.31 0.37 0.32 0.32 0.30 0.35 0.36 0.26 0.39 0,29 0.3r 0.31 coz* 31. 33 3r.24 30.23 31.68 31.16 3I.24 31.17 30.44 3t.O7 29.86 30.82 32.t2 29.81 Total 99.13 98.09 98.74 98.08 99.37 98.93 97.03 98.70 99,24 99,46 99.82 99.65 100.00

Nunbet of lons on the basis of I C03

0,8153 0.7926 0.9094 0.7531 0.8378 0.8178 0.7681 0.8895 0.8420 0.9685 0,883t 0.7586 1,0000 ca 0.1817 0,2040 0.0873 0.243a 0,1598 0.179r O.2286 0.1081 0.1s44 0.0287 0.1134 0.2385 Pb 0.0004 0.0002 0.0006 0.0003 0.ooo3 0.0001 0.0002 0.0001 0.0003 0.0005 0.0005 0.0004 Ba 0.0028 0.0034 0.0030 0.0029 0.0021 0. 0032 0. 0033 0.0025 0.0036 0.0028 0.0028 0.0027 I 1. E891 1.8879 1.8984 1.8830 r.8922 1.8905 1.8850 - 1.9017 1.8954 - 1.9065 dr32 c^lc. 1.8897 1.8881 1.8985 1.8839 1.8916 1,8906 1.8853 1.8954 1.8922 7.9022 1,8957 1.8861 r,9062 ^? s.0841(8F*5.0834(7) s.0984(7) s.0746(17) 5.0881(6) s.0854(9) s.0763(ls) 5.0944(7) 5.0888(11) s.1O2E(14)5.0936(6) 5.OiE9(8) 5.1059(7) 8'3317(14) 8.3211(17) 8.3759(14) 8.3005(26) 8.3389(r2) 8.3361(20) 8.30s9(26) 8.3602(16) 8.3440(22) 8,3992(Ls) 8.3619(12) 8.3154(17) 8.4207(t3) s.9847(r0) 5.9806(9) 6.0115(9) 5.9687(2s) 5.9920(7) s.9869(13) 5.9743(22) 6.0012(9) s.9917(11) 6.0r97(11) 6.0027(8) 5.9716(9) 6.0319(11) v ?r 2s3'5r(s) 252,97(6' 255.71(5) 2s1.41(11) 2s4.24<4) 2s3.80(7) 2s1.e0(11) 2s5.5s(6') 2s4.42(7) 25E.OO(7) 2s5.66(s) 252.20(6' 259,35(6) lneas. 3.63 3.59 3.73 3.59 3.64 3.66 3.77 3.648 3.626 i.718 3.598 3.663 3.645 3.610 3.706 3.668 3.771 3.700 3.594 3.780

*Caleulated to gioe C = S? + Ca + Ba + Pb. **?he eetiruted stafilard eyrors ate gioen in papenthese, and refer ta the Last deeimal place(s) FaALor qw?T!, WinfieLd, IJnion Count!, Pennsgloania (Iaphm and Geger, 19?2) Salen Rock CmWnA quafrA, Dublin, PuLaski Count!, Vi"ginia (Dietdch, 1960) D?eneteinfrut, Wnstet dist"ict, Westphalia, Ceman! (Hardet, 1964) Belton Quafty, Eaet Stone cap, ilise County, Vitginia (Mitchetl and p\@rr, 1961) Itud. HiLLs, Ba?st@, San Bemardina County, Califomia (Knapf, 1918) CLa! Center, jttM Caunty, ahio (Monison, 1935; HoM"d, lg'g) Frazet Duntile qe?"A, CLAde Aoenue, Otta6a, Ont@io (Sabim, 1968) Drensteinftut, 1"fi)n6te" dist?ict, ile s tpLnlia, Ceman!1 ( Earde!, 1g 6 I ) SaaLfeld, Thu?ingia, cemanA (Na reference aoaiLabl,e) 70 Silbertaal,Silbe?taal, Geman! (No ?efererce aoailable) '11 Mine"Da Mine; Caue in Rock, Hatdin CauntA, tllircis (c"ade and Nackmski, 1949; weller, Grogan and ?ippie, 1952) 12 Sauth Pittsburg, tr4arian Caunt!, ?ennessee (No refeterce '13 aDailabLe) Jahnsan MattheA Spec. pu"e S"CO"

Spindlestage work on what appearedto be opti- of material from the same quarry (#) shows a cally untwinnedmaterial yielded almost identical B slightlylower CaO content,9.85 percent, closer to the and T values.Checking the grainsby X-ray single lower of the two valuesthey reported.In the past, crystal techniques showed the presenceof sub- there was a question as to whether many of these microscopictwinning on (l l0). In general,the refrac- high-calciumcontents were due to admixtureof tiveindices were found to increasewith increasingCa CaCOr.The microprobeand X-ray resultspresented content and are approximatedby lines drawn be- heresuggest that this is not the case. tweenthe refractiveindices of syntheticSrCOr, a : The limited compositionalrange of strontianite 1.517,P: 1.663,I : 1.667(Swanson et al., 1954) coexistingwith a CaCOsphase suggests an immisci- andaragonite, a:1.5300,0: 1.6810,I : 1.6854bility gap in the systemCaCOs-SrCO".Holland et al. (Miilheim, 1888,in Palacheet al., l95l). (1963)precipitated strontianite and aragonitefrom aqueoussolutions at 96'C and demonstratedthe Results and discussion existenceof an immiscibilitygap between40 and 70 Resultsof the study are summarizedin Table l. mole percentSrCOr. Strontianite is thoughtto be a The microprobeanalyses show the strontianitesex- very low-temperaturemineral, most likely crystalliz- amined to be essentiallya solid solution along the ing at 0r near l00oC (Helz and Holland, 1965).Its SrCOr-CaCO,join, with Ca substitutingfor Sr up to occurrencein open vugsand veinssuggests crystalli- about 25 mole percent.Older analysesof CaO con- zation at very low pressures,probably at most equal tent of strontianitesin Palacheet al. (1951)indicated to the hydrostaticpressure of the groundwater. The valuesas high as 7.36weight percent, well within the rangeof strontianitecompositions found in this study extremevalues found in this study.Recent strontian- falls within the compositionallimits indicated by ite analyses,many only partial, also fall within the Holland et al. (1963)and predictedfrom the work of rangeof the samplesin this study,excepting for the Chang(1965) for conditionscoinciding with natural 1l percentCaO content found by Mitchelland Pharr conditions. (1969)for theBelton Quarry strontianite. An analysis The samplesstudied exhibit very limited sub- STRONTIANITE COM POSITION AND PHYSICAL PROPERTIES 1003

Ttsre 2. Equationsfor strontianitecomposition from cell parametersand density

Correlat 10n tion Coef ficient

oole Z SrCO, = -21]16.24 + LL62.84 (dt32,E) +0.95 (Eo1eZ srcOr) 0.9928

= -3885.02 + 702,03 (ao,l) +2,37 o.9523

= -L746.35 + 219.41 (bo,i) +1.00 0,9919

= -2156.62 + 373.83 (co,l) +2.26 0.9585

= -734.63 + 3.219 (v,i3) +o,79 o.9949

= -367.47 + 123.18 (p . ) +0.29 0. 9988 naE = -381.35+ 127.33 h ) +0,45 0,9985 syn stitution of Ba and evenless of Pb. Other strontianite and in Figure l. Measuredvalues of dB2are listedin analysesrarely indicate the presenceof these ele- Table I for comparison.From the estimatedstandard ments,reflecting either the minor role theseplay or, deviationsand correlationcoefficients of Table 2, it in the caseof Ba, coprecipitationwith Sr in the wet- would appearthat measurementof eitherdrs2, b, or V chemicalanalysis. The most Ba- and Pb-richstron- are equallysuitable for indirectlydetermining SrCOs tianite reportedis from the Suizamine (De Villiers, content.However, nieasurement of dgz using an in- l97l), whichcontains 3.71 mole percent BaCO' and ternal standardis most appealingfor its simplicity. 0.10 mole percentPbCOs. These are an order of The relatignshipsbetween composition and the magnitudegreater than the Ba and Pb contentsof the ialculateddensities for syntheticstrontianites and the samplesof this study. natural strontianitesof this study are included in The minor role of Ba in strontianiteis not the Table2 and shoyir in Figure2. Calculateddensities resultof unavailability,for severalstrontianite speci- were used becauseof the difficultiesin measuring mens in this study have barite matrices.The same densities.For comirarison,Table I contains the type of argumentcould be made for Pb, but asso- measureddensities which comparefavorably with the ciated Pb mineralsare lesscommon and not as in- calculateddensities. timate. Complete solid solutions on the SrCOs-BaCO,and SrCOg-PbCO,joins have been synthesizedat high temperaturesand pressures(Cork and Gerhard,l93l; Chang,1965; Chang and Brice, 1972),butan immiscibilitygap at lower temperatures is still possible.The ionic radius of Sr (-1.30) is similarto that of Pb (1.33),whereas the sizediffer- encewith Ba (l.47) is nearlythe sameas that with Ca (1.18),for nine-coordinatedions accordingto Shan- o< AJ non and Prewitt(1969). On this basis,an.immiscibil- ro

ity gap with BaCOais conceivable(Chang, 1965). E Immiscibility with PbCOsis lesslikely, and the lack of intermediatecompositions may be the resultof the rarity of solutionsenriched in both Pb and Sr. The samplesin Table I lie essentiallyon the SrCOg-CaCO,join, and their cell dimensionsare consistentwith thoseof syntheticstrontianites. The relation of Sr-Ca content with the various cell pa- t88 rametersfor strontianiteis summarizedin Table 2. 70 80 90 loo The d-spacingof the 132peak has been suggested as a Mole % SrCO5

good indirect measureof strontianitecomposition Frc. l. Calculated values of d* plotted against mole percent (Froeseand Winkler, 1966).Results for this parame- SrCO, content. The line is the regressionline ofTable 2 calculated ter usingcalculated dr", arealso presented in Table 2 for these spacings and compositions. 1004 J. A. SPEERAND M. L. HENSLEY.DUNN

- AND W. R. Bnlce (1972) Subsolidusphase relations in 3 aragonite-typecarbonates: IL The systemsCaCOr-SrCOr- PbCOgand CaCOr-BaCOr-PbCOa.Am. Mineral.57, 155-168. Conr, J. M. rxo S. L. GenHeno(1931) Crystal structure of the seriesof barium and strontiumcarbonates. Am. Mineral. 16. 't t-77. De Vtlltens,J. P. R. (1971)Crystal structures ofaragonite, stron- tianite,and witherite.Am, Mineral.X,758-76'7. Dtrrnror, R, V. (1960)Calciostrontianite from Pulaskiand Rock- inghamCounties, Ya. Am. Mineral. 45, lll9-1124. Fnonse, E. ero H. G. F. WTNKLER(1966) The system

o CaCOs-SrCOeat high pressuresand 500"C to 7N"C. Can. Mineral.8,551-566. Gnewe, O. R. lNo M. P. Nrcrowsxt (1949)Strontianite and witheriteassociated with southernIllinois fluorite. Science. ll0. 331. Hlnoen, H. (1964)Geochemische Untersuchungen zur Geneseder StrontianitlagerstAttendes Miinsterlandes.Contr. M ineral. Pet- rogr. 10,198-215. Herz, G. R. eNn H. D. HollnNo (1965)The solubilityand geologicoccurrence of strontianite.Geochim. Cosmochim. Acta, 80 90 too 29,1303-1315. Mole SrCO3 ,7o Hor-r-eNo,H. D., M. Bnocsrx,J. MuNoz lNo U. M. OxsurcH FIc. 2. Calculatedvalues of densltyplotted against mole percent (1963)The co-precipitationof Sr+'?with aragoniteand of Ca+'z SrCOr content.Solid circlesare syntheticstrontianites and open with strontianitebetween 90o and 100'C. Geochim.Cosmochim. circlesnatural strontianites. Regression lines are given by theequa- Acta, 21.95'l-9'17. tions in Table2, thelower for syntheticstrontianites, the upperfor Howrno, C. L. H. (1959)Celestite and fluoritefrom Clay Center, naturalstrontianites. Ohio. CleuelandMus. Natl. Hist Mus. News, l. 125-130. Kr.topp,A. (1918)Strontianite deposits near Barstow,California. U. S. Geol.Suru. Bull. ffi 1,25'l-270. The natural strontianitesyield somewhathigher LeeHru, D. M. rNo A. R. Geyen (1972)Mineral collectingin Pennsylvania.Penn. Geol. Suru. Bull. G-33, 135-136. densitiesthan the syntheticstrontianites as a resultof MtTcnrt-t-,R. S. eNo R. F. PHrnn (1961)Celestite and calcio- their Ba and Pb contents.The Ba- and Pb-richSuiza strontianitefrom Wise County, Virginia. Am Mineral. 46, mine strontianite plots well above both curves in I 89-l 95. Figure2. In contrastto the cdll dimensions,density is MonnlsoN,R. B. (1935)The occurrenceand origin of celestiteand very sensitiveto the presenceof theseelements. If fluoriteat Clay Center,Ohio. Am. Mineral.20,780-790. Pnrncnp,C., H. Brnunu AND FRoNDer-(1951) strontianite C. Dana'sSystem cbmpositionis determinedusing one of of Mineralogy,Vol. 2, 7th edition,John Wiley and Sons,New the cell parameterspacings, a check on densitywill York, 196-2@. give an indicationwhether Ba and Pb are presentin Rucrlrocr, J. eNn E. L. GesplnnrNr(1969) Specifications of a significantamounts or not. computerprogram for processingelectron microprobe analyti- cal data. Toronto, Universityof Toronto, Dept. of Geology, Acknowledgments 3'7p. SluNn, A. P. (1968)Rocks and mineralsfor the collector,Buck- We appreciatedonation of specimensfrom the Virginia Poly- ingham-Mont-Laurier-Grenville, Hawkesburg-Ottawa, techniclnstitute and StateUniversity collections and the useof the Quebec; Ontario. Geol. Suru. Can. Pap. 6'b5, 54. equipmentof the University'sMolecular Structures Laboratory. SHnNNor.r,R. D. rNo C. T. Pnewrrr 11969)Effective ionic radii in References oxidesand fluorides.Acta Crystallogr.B.25,925-946. SwnNsor.r,H. E., R. K. Fuynr nNoG. M. UcnrNrc(1954) Stand- ArrLeueN,DlNrBr- E. lNo Howlno T. EvnNs,Jn. (1973)Job ard X-ray diffraction powder patterns. Natl. Bur. Stand. Circ. 9214:Indexing and least-squaresrefinement of powderdiffrac- 539, VolumeIlI,73 p. tion data. Natl. Tech Inf. Serv., U.S. Dept. Commer., WELLER,J. M., R. M. GnocrN ANDF. E. Trerre(1952) Geology of Springfield,Virginia, Document PB 216 f88. the FluorsparDeposits of lllinois. Illinois State Geol.'Suru.Bull. CHrNc, L. L. Y. (1965)Subsolidus phase relations in the systems No. 76, 147p. BaCO'-SrCOr,SrCOa-CaCOs, and BaCOr-CaCOg.J. Geol.73, 346-368. - (1971) Subsolidusphase relationsin the aragonite-type carbonates:I. The systemCaCOr-SrCOr-BaCO". Am. Mineral. Manuscriptreceiued, August 19, 1975;accepted 56.1660-1673. for publication,February 25, 1976