Phase Relations in the systems pbs-Agrs-sb2ss and pbs-Ag2s-Bizsa

13 Pages·2007·1.17 MB·English

American Mineralogist, Volume6 0, pages6 2t-633, 1975
PhaseR elationsi n the systemsp bs-Agrs-sb2ss and pbs-Ag2s-Bizsa
Syrn N. Hooe'nNo Lurr L. y. Cserc
Departmento f Geology,M iami (lniuersity, Oxford, Ohio 45056
Abstract
Phaser elationsi n the systemsp bS-AgrS-SbrSa, nd pbS-AgrS-BirSsw eres tudiedi n the
temperaturer ange 300o-500'c using evacuatedg lassc apsulet echnique.T he pbS_AgsbS,
join showsa completes olids olutiona t 500oC,a miscibilityg ap between6 5 and 90 moti per-
centP bSa t 400oC,a nd at 300oCt he presenceo f two smalls olid solutionsb etween5 0 and 52
molep ercentP bS,a nd 25 and4 0 mole percentP bS.A nother solids olutioni ncludesth ec om-
positionso f andorite( pbAgSbrS.)r,a mdohrite( pbrAgrSb.Srr)a,n d fizelyite( pbuAgrSbsS16).
An extensives olids olutione xistsa longt hel illianite-pavonitejo in, andi rasa misciUitityg ap
between2 5 and 46 mole percentP bSa t 500'C. Pavonitea lso exhibitss olid sotutiont oward
galenobismutitAe.l ong the PbS-AgBiSjo, in, a completes olids olutione xistsb etween4 00o
and 500'C.
Correlationso f experimentadl ata obtainedi n this study with somen atural mineral as-
semblagews ere made.
Introduction The lengthso f capsulews erea s smalla s possibles o
Lead sulfosaltm ineralsa re widespreadin many that the vapor spacea bovet he chargew as lesst han
hydrothermaol res,b ut rarelyf orm a substantiaplo r- 20 percento f the volume. Samplesw ere heatedi n
tion thereof. In the systemsu nder consideration, horizontalm uffie furnacesi n which the temperature
more than seventy-fivseu lfosaltsh aveb eenr eported; was regulated+ 2'C. Temperaturews erem easured
someo f thesea re well establishedo,t hersd oubtful, by meanso f calibratedc hromel-alumethl ermocou-
ands till othersh aveb eend iscreditedIt. wast he pur_ ples and a Leeds and Northrup potentiometer.
poseo f this investigationto synthesizteh eses ulfosalt Chargesw ere initially heated at 200oC for about
minerals and to establisht heir phase relations. twenty-fourh ours to reactt he sulfur slowly prior to
Becausme osts ulfosalmt ineralsa red epositeda t low heatinga t the desiredt emperatureW. hen sulfur was
temperaturesl,a te in the ore mineral sequencet,h is no longer visible (one to two weeks),t he r,nixtures
investigationw as carried out in the temperaturewerec ooled,g roundu ndera cetoner,e -sealeidn new
range3 00o-500oCt,h e lower temperatured ictatedb y capsulesa,n da nnealedG. enerally,42d aysw ereu sed
the extremes luggishnesosf the reaction. for equilibrationa t 500oC5, 2d aysa t 400oC,a nd1 47
daysa t 300'C.B ecausere actionr atesa t 300oCw ere
ExperimentaPl rocedure extremelys luggish,t heses amplesw ereg round after
Elemental antimony (Baker analyzedr, eagent), about ten weeks,p elletizeda, nd annealedfo r ten ad-
bismuth (Baker analyzedr,e agent),l ead (MclB rea_ ditionalw eeks.
gent), sulfur (Fisher,U .S.p.),a nd chemicallyp re- At the end of the heat treatment,c hargesw ere
cipitatedA grS (A.D. Mackay, C.p.) were useda s quenchedin air. Somed uplicateru nsq uenchedin ice
reactantsA. ll have 99.99p ercento r betterp urity. waterr evealedn o differencein phasea ssemblageAs.s
Reactantsw erep reparedt o a total weighto f approi- a test of equilibrium, somes amplesw ere heatedt o
imately one gram each.A fter thoroughm ixing by completem elting,q uenchedin ice water,g round un-
light grindingi n an agatem ortar,t he reactantws ere dera cetonea, nd annealeda t the desiredte mperatures
sealedin evacuatedq uartz-glascsa psulesu singt he for the samel engtho f time aso ther experimentsT. he
techniqued escribedb y Kullerud and yoder (1959). finala ssemblageosf the samec ompositiontr eatedb y
the two techniquesw ere identical.
I Presenta ddress:G lass-Ceramic Research,C orning Glass Works, X-ray powder diffraction usingN i-filtered copper
Corning, New York 14850. radiation and reflectedl ight microscopyw ere used
621
S, N. HODA, AND L. L, Y, CHANG
for phasei dentification. T he d valuesw erem easured existingo n the AgrS-AgSbSj2o in weret aken from
usinga -tungsten(a o: 3.1648A ; Swansona ndT atge, Keighin and Honea (1969).E xtensionin to the ter-
1953)a s an internals tandarda, nd latticep arameters nary regionw asv isuallye stimatedfr om the ratioso f
+0.02 A were computedb y a program obtained solidt o liquidq uenchedp roducti n polisheds ections.
from Dr. T. T. Chen,C arletonU niversity,O ttawa, Pyrargyritef orms as fine dendritesi n all silver-rich
Canada. liquids on cooling. The liquid field on the anti-
mony-rich side terminatesi n the AgSbSz-SbzSg
The SystemP bS-AgzS-SbzSs eutectica t 450oC( Keighina nd Honea,1 969).
The thirty-threep hases,n atural and synthetic, Solid phasess table at 500oC are boulangerite,
reported in this system( Fig. l) have been sum- robinsonitez, inkenitea, ndorites olids olution,a nd a
marizedb y Changa nd Bever( 1973)P. hasere lations solid solution which extendsf rom a-miargyrite to
in the binary systemsP bS-AgzSA, gzS-SbrSsa,n d galena.T his solid solution,i n which therei s a dis-
PbS-SbrSaw ere studied by Van Hook (1960), ordereds ubstitutiono f Ag1+a nd Sb'+ ions for Pb'+
Keighin and Honea (1969),a nd Craig, Chang,a nd ions, is readily preservedo n rapid cooling from
Lees( 1973),r espectively. 500'C. The tie linesb etweenth is solid solutiona nd
Wernick (1960)a nd Godovikov and Nenasheva other phases( Fig. 2) were determinedf rom the shift
(1969af)o und that continuouss olids olution,w ith a in d2ovoa lueso f the solid solution.
disorderedN aCl-type structure, existed along the The compositiono f the robinsonites ynthesizedin
PbS-AgSbSjzo in. Godovikove t al (1972)r eportedth e this study, 6PbS. 5Sb2S3a, greesw ell with the
synthesiso f freieslebenit(e2 PbS' AgrS ' Sb'S') and reportedd ata of Craige t al (1973),b ut is at variance
brongniardite(2 PbS. 3AgzS. 3sbrss). with the formula, TPbS' 6Sb2Sefr,o m other studies
The chemicacl ompositionas nd latticep arameters(Robinson,1 948;B erry, Fahey, and Bailey, 1952;
of all the phasess ynthesizeidn the presents tudy are Jambor, 1968;a nd Garvin, 1973).E lectronp robe
listedi n Table l. Their phaser elationsa red iscussedanalysiso f robinsonitem adeb y Jambor( 1967)i n-
below. dicated a lead content (6 to 7 percent) consis-
tently higher than appropriate for the formula
PhaseR elationsa l 500"C TPbS. 6sbrse.T he solid solution rangeo f robin-
Phasere lationsin thes ystema t 500oCa res howni n soniter eportedb y Salanchai nd Moh (1970)w asn ot
Figure2 . The compositionso f the two liquid fields observed.
h@ ll ($t&hid!t.1970)
ftlrmeiq ha | {c.do.i.t , tgrl
ha rv (c.din, r9n,
fta lv lgtehi.t d, 19rc,
rl (cdiil d, tgBt
h@ ll lRoHns t$l
sM.nib PYrqtlpnib M'tdnu
Frc. I Phases reported in the system PbS (galena)-AgrS (acanthite-argentite)-
Sb,Ss (stibnite)'
THE SYSTEMS PbS-lgzS-Sb2ss AND PbS-Ag"S-Bi2S" oz5
Tesl-r 1. Lattice Parametersa nd Compositions of PhasesS ynthesizeidn the SystemP bS-AgrS-SbrS,
Composi tion
Name mol-e/" Crsyt. System a b c q, B y
Pbs ASZS Sb2S3
Boulangerite I L.+ 28.6 Monoclinic 2L.50 23.47 8.05 - 99.26
Robinsonite 54.54 AF AE Triclinic 16.41 L7.A9 4-O2 99.24 95.76 a9.46
Zinkenite 50.0 s0.0 Hexagonal 44.L3 a.64
B -Miargyrite - 50.0 50.0 Monoclinic 13.31 4.42 L2.93 - 98.53
Pyrargyrite - 75.0 25.O Hexagonal 11.07
Freies lebenite 50.0 25.O 25.O Monoclinic 7.66 12.69 5. 83 - 90.75
Diaphorite 40.0 30.0 30.0 Orthorhombic 15.86 31.99 5.95
Brongniard it,e 25.O 37.5 ?? c Orthorhombic 15.86 31.54 5.90
Andorite s.s. 33.3 l-6.7 50.0 Orthorhombic 13.04 L9.L7 4.29
Andorite s.s. 26.O 19.8 2+ .2 Orthorhombic 13.00 L9.26 4.27
Andorite s.s. 52.O 9.0 ?qn Orthorhombic 13.03 19.15 4.29
Galena - aq n '7 4 Cubic 5.883 : :
miargyrite
Galena - 70.0 15.0 15.0 Cubic 5.A23
miargyrite
Galena - 50.0 25.O 25.O Cubic
miargyrite
s.s.
Galena - 40.0 30.0 30.0 Cubic 5.760
mj-argyrite
s.s.
Galena - 14.0 43.0 43.0 Cubic 5.690
miargyrite
s.s.
o -Miargyrite - 50.0 50.0 Cubic 5. OUJ
Pbs-as25-Sb2s3
50fc
o sPbS. eib2s3 (BoulangErib)
SinC. Phm
o TrcPh6 zPbS. Sb2S3 ( Pha* lv)(Ganin, 1973)
A Thre Ph.s
o Phe repoltrd in tmrg
6PbS. 5Sb2% (Robinsonircl
PbS. Sb2% (Zinkonire)
As2S. Sb2S3
(o-mia.gyritel
Ftc. 2. Phase relations in the system PbS-AgzS-SbzSsa t 500oC
624 S. N, HODA, AND L. L. Y. CHANG
The compositiono f zinkenite,li ke that of robin- Pb.A&Sb'oS2sfr om analyseso f impure material.
sonite,h as been a point of disagreemenatm ong Donnaya nd Donnay( 1954)h, oweverr,e portedt hat
previous investigators.N uffield (1944)r eported its cell volume and densityc onsiderationfi t neither of
compositiona s PbS Sb2S8b, ut from density the two formulaeg ivenb y Ahlfeld. Obviously,m ore
measurementsH arris ( I 968) proposed 6PbS adequatea nalytical data ate neededt o establishi ts
7Sb2SrG. arvin( 1973)a nd Salanchai nd Moh (1970) chemicafl ormula,
supported this 6: 7 composition,w hereasC raig Fizelyitew asr eportedb y Nuffield( 1945)t o bev ery
et al (1973)p lacedi t at l:1. The resultso f pres- similart o andoritea nd ramdohritein X-ray powder
ent investigationa re in agreemenwt ith Craig et a/'s diffraction patterns,p olisheds ections,a nd specific
ratio. gravity. The structurei s orthorhombicw ith ao :
A run of composition6 9.22m olep ercentP bSa nd tf .t+, b" : 19.23,a nd co : 812 A. es for ram-
30.78m olep ercenSt brSsp roducedb oulangeritpel us dohrite, availablea nalyseso f fizelyitea re not consis-
a phased ifferentf rom any known minerals.I ts X-ray tent with a simple formula.
powder diffraction data agree well with Garvin's Calculationso f latticep arameters( Table l) failed
phaseI V (Garvin,1 973)A. ccordingto Garvin,p hase to show any significantc hangew ith compositioni n
IV hasa compositionb etween5 7a nd6 6m olep ercent the andorites olids olutionT. hisw asa lsor eportedb y
PbS and is stableb etween4 25" and6 00'C. Salanchi Nuffield( 1945)a nd Donnaya nd Donnay( 1954).
and Moh (1970)a lsor eportedp haseI V at 66 mole
percentP bS,b ut the incongruentm elting point and PhaseR elationsa t 400'C
lowers tabilityl imit weres tateda s 597"Ca nd 505oC, At 400'C (Fig. 3), the systems hows( l) a mis-
respectivelyN. o X-ray data werep rovideds o that a cibility gap along the PbS-AgSbSj,o in between6 5
comparisonc ould not be made. Craig et al (1973) and 90 mole percentP bS, (2) the disappearancoef
reportedp haseI I at 60 mole percentP bSm eltingi n- liquid fields, (3) a slight shrinkageo f the andorite
congruentlya t 603'C and with a lower stabilityl imit field, (4) the disappearanceo f phase IV, and (5)
undeterminedT. he threem osti ntensep eakso f phase the appearanceo f pYrargYrite'
Il area t 3.72,l0:3.166, ; and2 .855, .
Andorite displays- .extensivseo lid solution,a nd
PhaseR elationsa t 300'C
forms equilibriuma ssemblagewsi th all phasesin the
PbS-AgSbS2-Sb2hSasl f of the systeme xceptg alena. At 300"C (Fig. a) the PbS-AgSbSj,o in is marked
Fiver eliablea nalyseosf andoriteo, neo f ramdohrite, by wide miscibilityg aps,a nd by two solid solution
and one of fizelyite( Nuffield, 1945)a ll fall in the an- serieso, ne between5 0 and 52 mole percentP bSa nd
dorites olid solutionr egion( Fig. 2). It thus appears the other between2 5 and4 0 mole percentP bS,t his
that at 500"C thesem ineralsb ecomep arts of a solid latter spanningt he compositionalr ange from
solution. diaphoritet o brongniardite.
Donnaya nd Donnay( 1954)e xaminedth e density Robinsoniteh as a lower stabilityl imit of 318" +
and unit cell parameterso f museums pecimenosf an- l0oC on the PbS-SbrSgjo in. This lower stability
dorite and ramdohrite( 6PbS. 2AgzS' 5SbzSsa)n d limit may explaint he rarity of robinsonitein nature'
proposedt hat thesen amesb e replacedw ith andorite- Semseyite(9 PbS. 4sbrss)w as synthesizeda t 300"C
IV and andorite-Vl. Thesep hasesh ave identicala o from a compositiono f 69.22m ole percentP bS and
and bo values,e qualt o 13.03a nd 19.15A , respec- 30.78m ole percentS brSr;i t also appearedin as-
tively,b ut havec o-axisd imensionws hicha re multi- semblagews ith zinkenitea nd andoritei n the ternary
ples( 4c' and 6c') of a commonp seudo-periocd' : system. Semseyiteh as been synthesizedo nly
4.29L . Kawadaa nd Hellner( 1971)d eterminedth e hydrothermallyb y Robinson( 1948)a nd by Jambor
crystals tructureo f the sub-cello f andorite-VI( ram- (1968)a, nd its stabilitya longt hej oin PbS-SbzShsa s
dohrite)a ndc onfirmedD onnaya ndD onnay's( 1954) not been firmly establishedR. obinson reported an
data, upper stability of hydrothermally synthesized
Ramdohriteis the namea ppliedb y Ahlfeld( 1930) semseyitea t 415" + l0oc, but the absenceo f this
to a lead-silvers ulfantimonideo f probable com- phasein the presents tudya t 400"Cs uggestasn upper
position PbrAgzSb.S,o,r PbuAgnSbroSfrzogm Potosi, limit below 400"C. Other memberso f the plagionite
Bolivia. Harcourt (1942)n oted that its powder dif- group, plagionite (5PbS. 4sbrss), fuloppite
fraction pattern is very similar to that of andorite. (3PbS. 4sbrss),a nd heteromorphite(7 PbS' 4Sb2$),
Nuffield (1945) deduced the cell content, were not observed in the present investigation'
THE SYSTEMS PbS-Ig,S-Sb2S!A ND PbS-Ag,S-Bi2S' 625
o Singls Pha
o
TmPh6 5PbS. 2SbA (Bouthgorite)
A ThrePhs
o Phd Eporfid in nsttn
6PbS. 5Sb2S3 (Robinbnirc)
PHi 'Sb2S3 lZit*onab)
asf 3Ag2s.Sb2S3 l92S.Sr2S3 sbf3
(Pyrargyrite) (d-misrgyrire)
Ftc. 3, Phaser elationsi n the systemP bs-Agrs-sbrssa t 400oc. The abbreviation" and. ss"= andorite solid solution.
Miargyrite is presenta t 300"C in its monoclinic cubic-monoclinitcr ansitiont emperatureo f AgSbS,
form and has no detectablera ngeo f solid solution. (380'C) determinedis in agreemenwt ith Keighin and
The andorite solid solution is considerablyHonea (1969),b ut is 20oCh ighert han that deter-
diminishedi n sizea t 300oC,a nd a two-phasea s- minedb y Wernick( 1960).L atticep arameterosf the
semblageo f andoritea ndg alenais presentT. he limits NaCl-types olids olutiona longt hisj oin increasneo n-
of andorite solid solution correspondw ith the linearly with increasingP bS-content( Table I and
reported compositionso f andorite (pbrAgrSb.Srr)Fig. 6). Wide miscibility gaps exist between p-
and fizelyite (PbuAgrSbrS,ra),n d include the com- miargyrite and the brongniardite-diaphorites eries,
positiono f ramdohrite( pbrAgrSb.Srg). and betweenfr eieslebenitaen d galena,w hereasa nar-
Attainment of equilibriuma long the join PbS- row gap exists between freieslebenitea nd the
SbzSas t 300'C is questionablea,s evidencedb y the diaphorite-brongniardites eries.
presenceo f galenai n sampleso f boulangeritea nd The structureo f freieslebenitaen d diaphoritec an
semseyitec ompositions.W ithin the ternary region, be deducedf rom the galenas tructurea s shown by
however,e xperimentsw ith sampleso f as little as 5 Hellner( 1958).G odovikova nd Nenasheva(1 969a)
mole percentA grS appearedt o reache quilibriumi n noticed that three of five analysesg iven for
twenty-onew eeks.P hasea ssemblageosf semseyite+ freieslebenitefi t diaphorite (PbrA&SbsSr)a nd the
andoritea nd semseyite* zinkenite* andoritew ere remainingt wo can be calculatedto PbrAgnSbrSaun d
obtained. PbuAgrSbuS,Or.n the basis of new microprobe
analysis from museum specimenso f freieslebenite
PhaseR elationsA long the PbS-AgSbSJ" oin
from Freiberg and Braunsdorf, Germany, and
Phaser elationsa long the PbS-AgSbSj,o in are HiendelencinaS, pain, Sveshnikovaa nd Borodaev
showni n Figure5 ; thel iquidusa nds olidusc urvesa re (1972)o btainedt he formula PbAgSbSsw, hich is in
takenf rom Godovikova nd Nenashev0a9 69a).T he agreemenwt ith that obtainedb y Hellner( 1958)a nd
626 S. N. HODA, AND L. L Y CHANG
PbS-A92S-Sb2S3
3000 c
a Single Phas
o Two Phds
A Thre Phas 5PbS.2Sb2S3( Boutangerire)
9PbS.4Sb2S3(Semeyinl
PbS Sb2q (Zinkonitel
sbfs
Aef
3As25.Sb2S3 AszSS b2S3
(Pyra.gyrite, (6{iarttrite)
Frc. 4. phase relations in the system PbS-AgzS-SbrSsa t 300oC. Abbreviations are: Fr: freieslebenite,D i: diaphorite,
Br: brongniardite, and. ss: andorite solid solution'
in the presents tudy.A s for the diaphorite-brongniar- Ge ologicalS ignificance
dite seriest,h e former is a well establishedp hasea nd
is regarded as the best authenticatedo f the in- Andorite hasa largef ield of stabilitya nd cano ccur
termediate phases along the PbS-AgSbS2j oin, with almosta ll other leads ulfantimonidesIt. is one
whereast he latter is of questionablev alidity. of the major silverm ineralso f the ores at Oruro,
Recently, Godovikov and Nenasheva( 1969a) Bolivia, wherei t occursw ith zinkenite,b oulangerite,
reported a new syntheticp haseP bAgsSbaSwr,h ich plagionite, and small amounts of semseyite,
Godovikov et al (1972)c alled brongniardite.T hey freieslebenitem, iargyrite,s tibnite,a nd owyheeiteI.t
gavet he X-ray dataa nd chemicaal nd opticalp roper- is slightlyo ldert hano r contemporaneouwsit h other
ties of this syntheticp hase,b ut did not statew hether lead sulfosalts( Chace,1 948).W ith the exceptiono f
their X-ray data werei denticalw ith thoseo f natural owyheeitet he above associationis compatiblew ith
brongniarditeT. he phased escribedb y Godovikov the presentd ata. If owyheeite( Fig. l) forms at a
and Nenasheva(1 969b)h as alsob eenf ound in the temperatureb elow 300oC,i t could be one of the
presents tudy. youngestm emberso f the group, forming at the ex-
The limits of diaphorite-brongniardites olid solu- penseo f freieslebenitea,n dorite,a nd galena.I ts posi-
tion weree stablishefdr om runsa t 2 molep ercentP bS tion in the paragenetisce quencceo uldn ot established
intervalsb etweent heir stoichiometricc ompositions. by Chace( 1948)A. t Morey,N evada,h oweverW, il-
Attemptsw erem adet o determineth e phaser elations liam (1968)r eportedo wyheeiteto be the youngest
alongt hej oin PbS-AgSbSa, t Iowert emperaturebsy mineral and to have formed at the expenseo f an-
mixing the reactantsw ith KCI-AICI3 flux (eutectic dorite, fizelyite,f reieslebenitea,n d other sulfosalts.
composition)T.h er esultsw eren ot conclusiveP.h ases Two distinct specieso f andoritem ay occur in
obtaineda t 250"C wereB -miargyrite,f reieslebenite,naturea s syntaxici ntergrowths(D onnaya nd Don-
galena,a nd unidentifiedP -hases. tray, 1954). Recently, Borodaev et al (1971) te'
THE SYSTEMS PbS-Ag,S-Sb,SsA ND pbS-Ag,S-Bi,S" 627
examined ramdohrite from the type locality in
Bolivia and, reporteda n intergrowtho f light and dark
bandst hat yieldeds imilarX -ray diffractionp atterns.
Chemicala nalysegs avet he formula PbrAgSb3Sto,
the light band and PbAgSbrSt,o the dark band.
Natural occurrencesth, erefore,s uggestth e existence
of miscibilityg aps in the andorite solid solution
series.T here should perhapsb e two solvi below
300oC,o ne betweena ndoritea nd ramdohritea nd
the other between ramdohrite and fizelyite com-
positions.
The syntaxici ntergrowthso f memberso f the an-
J
dorite seriesa re particularlyi nterestinga s possible
temperaturein dicators.T he temperaturea t which
naturals amplehs omogenizoen heatingw ouldb et he
Frc. 6. Latticep arameters tffil"tf", PbSm olep ercenta long
", "
the PbS-AgSbSj,o in
minimum temperature of deposition. Brongniardite-
miargyrite exsolutionc ould similarly be used,b ut the
rarity of brongniardite would greatly limit its applica-
tion.
In a recent study of the Wood River lead silver
deposits, Hall and Czamanske (1972) found
diaphorite and Ag-boulangerite as inclusions in
galena. The Ag-boulangerite has a composition
(Pb,Ag,Cu)u.n Sbou S1ri,n termediate betweenb ou-
langerite and owyheeite. Neither Ag-boulangerite
nor owyheeitei s stablei n the systemP bS-AgrS-SbrS,
(J
o 700 in the temperature range of the present study.
3
o The System PbS-AgrS-BirS,
o
o
o Twenty phasesr eported to belong to this system
F 600
are shown in Figure 7. Relevantd ata on thesep hases
are summarized in a recent review by Chang and
Bever (1973). Phaser elations in the binary systems
oa oo ooa AgrS-BirS, and PbS-BirS3w ere studiedb y Van Hook
(1960) and Craig (1967),r espectively.
On the basiso f natural intergrowthso f galenaa nd
420 1 10. c
matildite, Ramdohr (1938) suggesteda n extensive
solid solution along the PbS-AgBiS, join. The crest
of the solvus was estimated by Ramdohr at about
----o-qo
. tfd 350'C. Van Hook (1960) failed to determine the
o o o\ooa a o oo ooo solvus but reported the unmixing of a sample of
AgBiS, containing 3.9 mole percentP bSw hen held at
frss+glss 170'C in three months. Craig (1967) obtained com-
plete homogenizationo f a natural samplec ontaining
36 mole percent PbS at 225'C. Godovikov et a/
Mol % PbS
(1972) found that the seriess hows a miscibility gap
Ftc. 5. Phase relations along the PbS-AgSbS, join. Symbols, below 220oC forming schirmerite (PbS . 2Ag,S .
solid circle: one phase; half-filled circle: two phases. Abbrevia-
tions are: miarg: miargyrite. di: diaphorite, fr: freieslebenite,g l: 2BirS3)a nd an unmixed cubic solid solution (60-
galena, ss: solid solution. 90 mole percent)a I 150"-220"C.
628 S. N, HODA, AND L. L. Y CHANG
hd ll lcrdf, 1S7)
M lll lQir,lgTl
trGbin
hrx o
lxNrklk. rgm,
Gudio O
lKnFMdb, ltrc,
ArPE 356 o
lrdFHh,leDl
Sdri|ffiib o
Mdin Mdtdo
Ftc. 7. Phasesre portedi n the systemPbS (galena)-AgrS(a canthite-argentite)-Bir(sb"i smuthinite)
Investigationsin the systemP bS-AgrS-BizSw, ere by Craig (5.648A ). The variationi n ao along the
carriedo ut by Van Hook (1960)B. ecaushei sp rimary PbS-AgBiSzjo in and the effecto f excessA grS and
objective was to study the solubility of silver in BizS,o n ao also agreew ell with Van Hook's re-
galena,h e establishedp haser elationso nly in the sults.T he substitutiono f Ag'+ and Bi8+f or 2Pb'z+is
galena-matildite solubility region. Craig (1967) not so easilye xplainablew hen the Ag:Bi ratio de-
showedt he phaser elationso n the PbS-AgzS-BizSgparts from l:1. Suchs olid solutionsc an arisef rom
planed educedfr om experimentcso nducteda longt he cationic or anionic vacancies,o r interstitial oc-
PbS-AgBi'Sua nd PbS-AgBiSzjo ins in the system cupancyt o balancet he charge.I f it is assumedth at
Pb-Ag-Bi-S. the large 52- ions form rigid frameworks within
All phasess ynthesizedin the presents tudy with which the relatively mobile metallic ions normally
their chemicalc ompositionsa nd lattice parameters occupyt he octahedrasl ites,it is possibleth at some
arel istedi n Table2 , andt heir phaser elationsa red is- tetrahedralo ccupancyt akesp lace on the silver-rich
cussedi n the following isothermals ections. side and vacant cationic structural positions are
presento n the bismuth-richs ide of the solid solu-
PhaseR elationsa t 500"C tion.
At 500'C (Fig. 8) stable phases include Tie lines betweeng alena-matildites olid solution
heyrovskyiteli,l lianite,g alenobismutitpea, vonitea, - series and other phasesi n the systemw ere con-
matildite,a rgentiteb, ismuthinitea,n dg alenaG. alena structedo n the basiso f the shift of dzovoa lueso f the
and a-matilditef orm a completes olid solutions eries NaCl-typep hases.
with the disorderedN aCl-types tructure'a -matildite At 500'C, an extensives olid solution existsa long
can accept Bi2Sa and AgzS in exces s of its the lillianite-pavonitjeo in with a miscibilityg apb e-
stoichiometricc ompositionT. he limits were deter- tween 25 and 46 mole percent PbS' The pavonite
mined as 5 mole percentB izSsa nd 8 mole percent seriesa lso has a solid solution range toward
AgrS, by the appearance-of-phamsee thod. Samples galenobismutitEe.x perimentcso nducteda t tcmpera-
in which thesel imits aree xceedesdh owp avonitea nd iures above5 00"C (Fig. 9) show that meltingn ear
acanthitep owderd iffractionp eaks,r espectivelyT. he 670"Cp recludesc ompletes olid solutionb etweenli l-
aoc ell edgeh ered eterminedf or a-matildite (5.64A ) lianitea nd pavonite.
agreesw ell with that givenb y Van Hook (5.64A ) and Lillianite wash eres ynthesizefdr om a composition
THE SYSTEMS PbS-,4g,S-Sb2SAs N D PbS-Agz,S-BizSa
of 73 mole percentP bS and 27 mole percentB i2Ss.molep ercenPt bSa nd l8 molep ercentB i2Ssg aveX -
The X-ray diffractiond ata agreev ery well with those ray diffractiond ataw hich correspondw ell with those
given by Craig (1967) for his phase III. Cor- of heyrovskyit(eK lominskye t al, 1971)a, ndp haseII
respondingp hasess ynthesizedb y Otto and Strunz (Craig, 1967)E. xperimentsto checki ts lowers tability
(1968), Klyakhiv and Dimitriyeva (1968), and limit showedn o signo f breakdowna t325oCin 3000
Salanchia nd Moh (1969)h ave beens hown to be hours( Craig, 1967)S. omen aturals amplesh, owever,
similart o Craig'sp haseI II, as well as to naturall il- show cosalite-galenaa ggregatesp seudomorphous
lianite( Klyakhiva nd Dimitriyeva,1 968T; akagia nd after heyrovskyite( Klominsky el al, l97l). The lat-
Takeuchi, 1972).T he lattice parametersd etermined tice parameters determined for this phase
in this study for silver-freeli llianite (Table 2) are in (heyrovskyitein Table 2) agreew ell with thoseg iven
fair agreementw ith those given by Takagi and by Klominskye t al (1971)f or a naturals amplec on-
Takeuchi( 1972)f or a natural sampleo f lillianite tainingm ore than I percentA g in solids olution( ao:
from Tsubakiharam ine, Japan( ao : 13.535b, o : 13.705b, o : 31.19c, o : 4.121A ).
20.451,c o : 4.104A ). Chemicala nalysiso f their Galenobismutitew as synthesizedfr om a PbS
specimenis not given, but the specimenis statedt o BirSr composition.P haseI V, reported by Craig
containa smalla mounto f silver. (1967),h as identical X-ray diffraction data though
Pavonitew as readily formed at all temperaturesits compositioni s statedt o be 48.7 mole percent
within the rangeo f the presenti nvestigationL. attice PbS and 51,3 mole percent Birss. Lattice pa-
parameters(T able2 ) are in fair agreemenwt ith those rametersd eterminedi n this study (Table 2) are in
given by Nuffield (1954)f or a natural samplef rom good agreemenwt ith thoseg ivenb y Berry (1940)f or
Porvenirm ine,B olivia( ao: 13.35,,o : 4.03,c o: a natural sample from Nordmark, Sweden( ao :
16344 ,0 : 94,50")T. he presencoef smalla mounts 11.74b, o : 14.55c, o : 4.08A ).
of Pb, Cu, and Fe, as indicated by the chemical
analysiso f this specimen,m ay account for the PhaseR elationsa t 400'C
difference. At 400"C( Fig. l0) thea -matildites olids olutioni s
A phase synthesizedfr om a compositiono f 82 limited along the AgrS-BirSsjo in to between4 5 and
TlsLr 2. Lattice Parametersa nd Compositions of Phases
Synthesizeidn the SystemP bS-AgrS-BtSg
Composi tion
Name mole% Cryst. System
PbS Ag2S Bi2S3
Heyrovskyite 82.O - 18.0 Orthorhombic 13.71 3t.46 4.L3
calenobismutite 50.0 - 50.0 Orthorhombic 1r.61 13.57 4.08
,Bismuthinite 100.0 Orthorhombic 11.17 11.30 3.99
Lillianite 73.0 - 27 .O Orthorhombic L3.47 20.75 4. L3
Lillianite s.s.65.0 2.9 32.L Orthorhombic t3.44 20.66 4.L5
Lillianite s.s.60.0 5.0 35.0 Orthorhombic 13.37 20.43 4.r3
Lillianite s.s. 53.0 7.O 40.0 Orthorhombic 13.41 20.29 4.L2
Lillianite s.s.48.0 A.7 43.3 Orthorhombic 13.40 20.L2 4.LL
Pavonite - 25.O 75.O I"lonoclinic 13.30 4.O4 15.43 J+.LV
Pavonite s.s. 4.0 23.O 73.O Monoclinic 13.31 4.05 L6.4I o2 7?
Pavonite s.s. 12.O 2l.O 67.O Monoclinic 13.3s 4.06 ]-6.47 94.68
Pavonite s.s. 15.0 20.0 65.0 Monoclinic 13.36 4.06 L6.49 94.07
Pavonite s.s. 20.0 18.0 62.O Monoclinic 13.35 4.O7 16.50 93.60
Galena - I0.0 45.0 45.0 Cubic 5.68
matildite s.s.
Ga1ena - 20.0 40.0 40.0 Cubic R?N
matildite s.s.
Galena - 30.0 33.8 36.2 Cubic 5.7L
matildite s,s.
Galena - s0.0 25.0 25.O Cubic 5.77
matildite s.s.
Galena - 70.0 15.0 1s.0 Cubic 5.82
matildite s.s.
Galena - 80.0 10.0 10.0 Cubic 5.86
matildite s.s.
o -MatiLdite - qn n Cubic
630 S, N. HODA, AND L L Y. CHANG
PbS-As2s-Bi2s3
500pc
82PbS. 18Ai2E (Heyrovskyitel
a
SinglGP ha$
73 PbS . 27Bi2S3 (Lillianite)
o Two Phas
A Thre Ph@i
PbS.B i2t {c.tenobismuritel
a
o
oa
o
oa: a
ag2s.a i2fu A92S. 3Bi2S3
(d-matildite) (Pavonitcl
Ftc 8. Phase relations in the system PbS-AgrS-BirS, at 500oC.
55 molep ercentB irSr,w hereasg alenac ant ake only2 two- and three-phase assem blages containing
molep ercenBt irS3in solids olutionT. hec omposition heyrovskyite. The lillianite-pavonitem iscibility gap
of galena-matilditseo lids olutioni n equilibriumw ith has widenedt o betweenl 0 and 48 mole percentP bS.
heyrovskyitea nd lillianites olid solutionh as shifted The most striking feature at 400oC is the disap-
from 68 molep ercentP bSa t 500'C to 85 molep er- pearanceo f galenobismutite.R uns conforming to its
cent PbS at 400oC,t hus narrowingt he regionso f composition and those adjacent to it in the binary
and ternary regionsc onsistentlys howedl illianite and
bismuthinite instead of galenobismutite. Several
repeated attempts gave identical results at 400oC for
a period of 8 weeks, although Craig (1967) and
Salanchia nd Moh (1969)h ave reported its synthesis
aaa a Pryonito
LillianitgS olid Solution Solid Solution at 400oC or lower. At 420"C for the same length of
aaaa o o oo aa a time galenobismutite was synthesizeda s a single
phasef rom the composition PbS . Birss. We do not
aaa o o o oo
understand the discrepancyb etween our data and
those of Craig (1967)a nd Salanchia nd Moh (1969);
nevertheless,w e believe galenobismutitet o be un-
stable below 400'C and support this further with
evidence from natural occurrences.
Phase Relations at 300"C
010 20 30 40 50 60 70 80 90 100
Lillianile Mot % Pavonite Experimental runs at 300'C failed to reach
Frc. 9 Phase relations between pavonite and lillianite. equilibrium in a period up to thirty weeks.A ttempts