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Strontianite Composition and Physical Properties

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Strontianite Composition and Physical Properties 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 .
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