Canadian Mineralogist
Vol.23, pp. 6l-76 (1985)
THE RELATIONSHIP
BETWEENCRYSTALSTRUCTURE,BONDINGAND
CELLDIMENSIONSIN THE GOPPERSULFIDES
RONALD J. GOBLE
Deportment of Geology, University of Nebrasko-Lincoln,
433 Morrill Holl, Lincoln, Nebrosko 68588-0340,U.S.A,
ABSTRACT
de cui'ire de structureconnueindiquentque la structure
de la yarrowiteet cellede la spionkopiteressembleraient
Copper and copper-iron sulfidescan be classifiedinro surplusieurs
pointsi celledela covelline,maison doit conthree generalgroups: (1) anilite, digenite,geerite,cubanite, siddrercommeprobableuneoccupation
statistique
dessites.
chalcopyrite, haycockite, talnakhite, mooihoekite and bor- Lestentativesdeddtermination
dela structuredela spionnite with structuresbasedupon approximatecubic close- kopiteont 6t€entravdes
par I'imperfectiondescristauxet
packing of the sulfur atoms; (2) djurleite and chalcocite le grandnombrede sitesde cuivrevacants.La stru4ure
with structures basedupon approximate hexagonal close- de la geeriteestrhomboddrique
(fi32?), a 15.77A, a
packing oftle sulfur atoms; (3) covelline,yarrowite, spion- 13o56'
i cellede la digdnite.
, Z = l, et ressemblerait
kopite and idaite with a combination of hexagonalclosepacking and covalent bonding of the sulfur atoms. The
average spacing D between layers in all groups can be
expressed
asD = 2.M3 + 0.654(Cu:S)+ l. 183@e:S).The
ionic radius R of sulfur for group-l mineralsis R, = 2t7
Q'l2A), where D is from the previous expression;for
group-2 minerals, Rz = 1.856+ 0.060 (Cu:S)+ 0.023
@e:S);for group-3minerals,R: = 1.857+ 0.039(Cu:S)0.020 @e:S). Consideration of bond lengths in coordination polyhedra of known copper sulfide structures
indicatesthat major portions ofthe yarrowite and spionkopite structures will resemblethe covelline structure. vdth
probable statistical site-occupancy.Attempts at the determination of the spionkopitestructurewere hamperedby
the imperfection of the crystals and the partial occupancy
of most structural positionsof copper. The geeritestructure is rhombohedral(R3n?) with a 15.77A, o 13.56,.
Z = l, and will probably resemblethe digenitestructure.
Keywords: yarrowite, spionkopite, geerite,copper sulfides,
copper-iron sulfides, blaubleibender covelline, crystal
structure, bonding,
SoMMAIRE
On peut regrouperles sulfuresde cuivre et de cuivre r
fer en trois grandesfamilles: l) anilite, dig6nite,geerite,
cubanite, chalcopyrite,haycockite,talnakhite, mooihoekite et bornite, dont la structure contient un empilement
approximativement cubique compact des atomes de soufre; 2) djurl6ite et chalcocite,dont la structuremontre un
empilementhexagonalcompact (6rossomodo) desatomes
de soufre, et 3) covelline,yarrowite, spionkopiteet idaite,
qui montrent une combinaison de I'agencementhexagonal
compacfdesatomesde soufre avecliaisonscovalentes.Pour
lestrois groupes,la s6parationmoyenneD descouchesest
6galed I'expression
2.063+ 0.654(Cu:S)+ 1.183(Fe:S).
Le rayon ionique.R du soufre Cansles min6raux du premier groupe est 6gal d D/2 l2A. Pour les mindraux ou
: 1.856+ 0.060(Cu:S)+ 0.023
deuxidmegroupe,on a .rR2
(Fe:S), et pour ceux du troisiime groupe,
R: = l.8SZ + 0.039 (Cu:S) - 0.020 @e:S).Les longueurs
de liaisons dans les polybdresde coordination des sulfures
61
(Traduit par la R6daction)
Mots-clds:yarrowite,spionkopite,geerite,sulfurc decuivre, sulfuresdecuivreet fer, covellineblaubleibender,
structurecristalline,liaisons.
INTRODUCTIoN
Eight copper-sulfideminerals havebeenidentified
to date: covellineCul.6gs,yarrowite Cu1.12S,
spionkopite Cu,.*S, geeriteCu1.6eS,
anilite Cut.75S,digenite Cu,.*S, djurleite Cu1.eSand chalcociteCuz.mS.
Partial or completestructural determinationshave
been carried out for covelline (Oftedal 1932,Berry
1954,Kalbskopf et al. 1975,Evans& Konnert 1976),
anilite (Koto & Morimoto 1970),digenite(Donnay
et al. 1958,Morimoto & Kullerud 1963),djurleite
(Takedaet al. 1967a,b,Evans 1979),and chalcocite
(Sadanagaet al. 1965,Evans l97l). The structures
of yarrowite, spionkopiteand geeritehavenot been
determined.Yarrowite and spionkopite,two of the
blaubleibenderor "blue-remaining" covellines,were
for many yearsdescribedin terms of the hexagonal
unit-cell of covelline,basedupon similaritiesof Xray powderpatterns(e.9., Frenzel1959,Moh 1971,
Rickard 1972,Putnis et ql. 1977),However, Goble
(1980)hasshownthat the unit cellsof yarrowiteand
spionkopite are not the sameas that of covelline.
Geeriteis a pseudocubiccopper sulfide that has only
recently been reported (Goble & Robinson 1980).
The known structurescan be divided into three
generalgroupsbasedupon the natlue of packingof
the sulfur atoms: (l) anilite and digenite,with structuresbasedupon approximatecubic close-packing,
(2) djurleite and chalcocite,with structuresbased
upon approximate hexagonalclose-packing,and (3)
covelline, with a combination of hexagonalclosepacking and covalentbonding of the sulfur atoms.
62
THE CANADIAN MINERALOGIST
The resemblancebetweenthe well-developedyarrowite and spionkopite subcellsand the covelline
unit-cell (Goble 1980)suggeststhat theseminerals
belong to group 3; the pseudocubicnature and
resemblanceof the geeriteunit-cell to a structureproducedby the leachingof anilite (Goble 1981)suggestthat geeritebelongsto group 1. Single-crystal
X-ray studiesprovide a method of examiningthe
structuresof yarrowite, spionkopiteand geeriteand
of determiningthe true relationshipbetweenthese
structure$and those alreadyknown for other copper sulfides.
PRoCEDURES
Cleavagefragmentsof yarrowite, spionkopite and
F
t.c
f
]t
A. COVELUNE
B. COVELUNE
0120)ptone
I*I
T
IT
-t_
C.'ANIUTE"
(100)
phne
l_Jl
tY I
)-)
A
l..-/.........---.....n
D.SPHALERITE
geeritefrom the studiesof Goble (1980)and Goble
& Robinson (1980)were used for all single-crystal
patterns. Precession,Weissenbergand integrated
Weissenbergphotographswere preparedfor selected orientations of the yarrowite and spionkopite
reciprocallattices.Precessionphotographsof covelline in the equivalentorientationswere also prepared in order to checkthe supposedstructural similarity of the blaubleibendercovellinesto this mineral.
For geerite,only precessionphotographswere prepared. Filtered Cu-radiationwas usedfor all Weissenbergfilms and Mo radiation for all precession
films. The fragmentsof yarrowite, spionkopiteand
geeriteusedmeasureapproximately0.14 x 0.08 x
0.03,0.25 x 0.08 x 0.08and 0.07 x 0.06 x 0.02
mm, respectively.
For intensity determinations,0-, l- and 2level
integratedWeissenbergphotographs(rotation axis
c), weretaken of the yarrowite and spionkopite fragments.Exposuretimes for all levelswereon the order
of 200hours using a Philips fine-focusCu X-ray tube
(point-focusport) with a Philips PW 1008/85selfrectified high-voltagepower supply operatingat 40
kV and 12mA. Three-film packswereused,the films
being separated by one sheet of black paper.
Individual films of eachpack werescaledusing the
"film factor" of Morimoto & Uyeda(1963).Different levelswerescaledby a comparisonof reflections
present on two or more of the levels, with the
assumptionthat the unit cellsare approximatelyhexagonal.
Intensitieswere estimatedby visual comparison
with the {110} reflection of covellineon standardUnobscalefilms preparedfrom multiple exposures.
servedreflectionswere assignedmaximum intensities of one-half the minimum observableintensity
at that point on the film. Raw intensity-datawere
correctedfor Lorentz and polarization effectsand,
in the caseof spionkopite,for the presenceof minor
(= l59o) intergrownorientedyarrowite; absorption
correctionswere not applied. Wilson plots (Wilsgn
1942)show^overalltemperature-factorsof 0.45 A2
and 0.75 A2 for yarrowite and spionkopite, respectively.
E. METASTABLE
DI6EMTE
Frc. 1. The crystal structure of covelline(after Wuensch
1974),"anilite", sphaleriteand metastabledigenite.The
"anilite" structureis an idealizedversion(seetext). In
B t,Cu and tvCu indicate copper atoms in triangular
and tetrahedralco-ordinationpolyhedra,respectively;
S. indicates covalently bonded sulfur; lC and lI
representthe spacingsof one covalentlybondedand one
tetrahedral (ionically bonded)layer, respectively.Filled
circlesin A, B and D indicate fully occupiedtriangular
co-ordination polyhedra; filled and open triangles in C
and E indicate fully and partly occupiedtetrahedral coordination polyhedra,respectively,with atomic displacement toward the four surroundingtriangular faces.
DATA
STRUCTURAL
The crystal strucure of covelline, a group-3
mineral,is shownin Figure la (after Wuensch1974);
equivalentsitesfor all atomslie on the (l l0) plane,
and the structure can be representedby a section
through the unit cell on this plane asshown in Figure
lb. The crystal structure of anilite, a group-l
mineral, can be representedin a similar fashion if
the structural data of Koto & Morimoto (1970)are
transformed into an idealized cubic close-packed
unit-cell. Copperatomsin triangularly co-ordinated
sitesare assignedto the tetrahedraof which these
63
CRYSTAL STRUCTURE OF THE COPPER SULFIDES
a11.tlt3
Oooe
r663
a88e
Oli3
a-LZ1
.057
.T7.nn
4776
.n.n.i
)zza
o635
olo.fit.m
415.15.15
)zzt
a$r
Ods-0
.t3.f3.tz
oiiS
a66s-
an.ji.i3
i"
a7.t7
FIc. 2. The reciprocallattice of geeritewith rhombohedralindices.Both rhombohedral and cubic crystallographicaxesare indicated.
sites form a face, and displacementof the copper
atoms from thesetetrahedrally co-ordinatedpositions areignored.A sectionthroughthis '(idealized"
structure of anilite perpendicularto the close-packed
layersof sulfur is shown in Figure lc; reduction of
the cell dimensionsnecessitates
averagingfull and
empty tetrahedraand resultsin partial (%) occupancy
by copper for some tetrahedra. The structure of
metastabledigenite(Morimoto & Kullerud 1963)in
the equivalentorientation is shown in Figure le. The
crystal structuresof djurleite and chalcocite,group-2
minerals,involve extensivetriangular co-ordination
of Cu and cannotreadily be representedon sections
suchas lb, lc and le. Because
ofthe strongresemblance betweenthe X-ray patterns of geerite and
sphalerite,a sectionthrough the sphaleriteunit-cell
in this orientation is representedin Figure ld.
Goble (1980,Figs. l, 2) showedthat the reciprocal latticesof yarrowite and spionkopiteare similar
to but distinct from that of covelline.Yarrowite Xray data were lndexed on a hexagonal cell with a
3.800,c 67.26A; spiopkopitewasshow4to be hexqsonal, with a 22.962A (i.e., 6 x 3.8n X), c 4t.429
A. Well-developedsubcellswith the approximate
{imensionsof the covellineunit-c€ll(a 3.796,c 16.36
A) were noted. Tables I and 2, which list the
observedstructure-factorsfor yarrowite and spionkopite, have been submitted to the Depository of
UnpublishedData, CISTI, National ResearchCoun-
cil of Canada,Ottawa, Ontario KIA 0S2.For yarrowite, I 17nonequivalentreflectionswereobserved,
623 were unobserved(only lF1,e1lvaluesare listed
in Table l, lF*:'l = lFnrrl). For spionkopite,147
nonequivalentreflectionswere observed,406 were
unobserved;all supercellreflectionsof the tpe hkl
wfih h or k + 6n were ignored (i.e., the
a' : a/6 = 3.8?i/A subcellwasused).Examination
of the structurefactors indicatesthat the spacegxoup
for both yarrowite and spionkopiteis one of .P5ra1,
P 3 m l , P 3 2 1 ,H l m , H l m o r B l 2 .
Geeritewas describedby Goble & Robinson(1980)
asbeingpseudocubic(possiblyorthorhombic),space
groupF43m. Careful re-examinationof precession
photographsshowsthat geeritecan be assignedconsistentindicesbasedupon a rhombohedralunit-cell
similar to that proposedfor digeniteby Donnay e/
TABTE
3.
IATA
ANDCUBICII{DICES FORI1IE GEERITEPOIIDER
r/r1
3. t28
2
' I .. 7
91
12
8
1.870*
'1.576
1.247
1.109
rrcflectlon
100
l0
50
l0
l0
30
l'10
0
20
Rhmbohedral Ind'l @s
Cubic lndices
221, 555
334
776
ll3,889
442,10.10.10
997,15.15.t5
il2, 13.t3.14
not obseryed on sJngle-crystal
patterns
3ll
222
422
64
THE CANADIAN MINERALOGIST
o
o
o
a
a
O
o
Oor
O
o
a
1u11u32u1.
orarOsvtovlev,
a
hlflrrr
a
o
'
o
w36ut72n
o
o
aoautsznln
ota
o
o
a
a
o
ln:rnifr.OO,
oT cilTtVtTn
o
o
o
hl01c
ouraraoz!'or
a
a
o
a
FIc. 3. The reciprocal lattice of anilite after leachingin ferric sulfate solution for
twelvehours. Rhombohedralindicesconsistentwith the geeriteunit-cell are shown.
Open circleslabeledT representreflectionsattributed to the secondindividual
of a twin.
a/. (1958).The geeritereciprocallattice, indexedon
this basis,is reproducedin Figure2; the X-ray powder pattern with both pseudocubicand rhombohedral indexingis givenin Table 3. Geeriteis rhombohedral Cu6S5(diffraction aspect R*1) with a
15.77A, a 13"56', Z = l, spacegroupR3m, R3m,
or R32. These data are consistentwith the weak
bireflectanceand moderateanisotropismobserved
by Goble & Robinson (1980).
The choice of the rhombohedral cell for geerite
is substantiated by the leaching experiments conductedby Goble (1981),which produceda structure
similar to that of geerite.The reciprocal lattice of
this material is shown in Figure 3; indicesrefer to
the geeriterhombohedralcell. Fractional indicesindicate that the leachedphasehas approximately tJree
times the a dimension of geerite (a,1,47.L2 A, a
4"40'). Careful re-examinationof reflection intensitieson precessionfiLns of leachedanilite showsthat
reflections indicated by open circles in Figure 3 are
produced by twinning about [00]*]" or [110*]".
Converting the rhombohedralcell tp a hexagonalcell
producesa length cpu of l4\.2 A, approximately
twice that in yarrowite (67.26A), thus explainingthe
resemblanceof the two phaseson X-ray powder patterns, a$ noted by Goble (1981).
Relationship betweenstructure and composition
The five known copper sulfide structures have
either approximately cubic or hexagonal closepackedlayersof sulfur or, in the caseof covelline,
a combination of hexagonalclose-packedwith covalently bonded layers of sulfur. In an ideal closepacked netwqlk the distance D between layers is
equalto 2R l2A, whereR is the radius of the sulfur
atoms. In copper sulfides such as covelline, with
OF
DISTAI{CE
BnIIEEIISULruRTAYERS(O) AI{ORADIUS
TABLE4. AVERAGE
(R) IN C'OPPER
SULFIDES
TAYERS
SULFUR
AIO.ISUTIFIN SULFIJR
D (8)
hkr
R (i)
@ell'lm
vafMlte
;plonkopite
geerite
anlllte
2.735
2.7
2.964
3.128
3.20B
006
0.0.24
0.0. 14
555
[email protected]
dlgenlte
3 . 2 1 6 555
3.200
3 . 6 2 BO0
3.373 h4
1.8971
ll0
Poltet & Evans(1976)
ll0
Goble (1980)
1.899
1.910
660 Coble (19B0)
776 Table 3
1.918
1.%3 040,400, Potter & Evans (1976)
224
1.969 10.10.0 ilorlrcto & Kullefud (1963)
oonnayet al. (1958)
1.959
1.9556
046 potter & Evans (1976)
(30
Potter & Evans (1976)
1.974n
nlreral
dJur'lelte
chalcoclte
hkr
data source
For anilite D is taken on the averageof the four nonDarallel-il1!i pl'nes
in the pseudocublc cell, that-ls, the orthoah@bic (0221 arld 12021
olaFs rith sDacinqsof 3.198 X and 3.2i8 A, respectively; R ls
i.aken as the rciqhted averaqe of the six mn-parallel t440' pseu@cubic planes, th;t ls,-the odiorh@blc (40!), {040}, an! t224} plares
xith spacingsof 1.977X' 1.953I, and 1.962A. respectlvelv.
65
CRYSTAL STRUCTURE OF THE COPPER SULFIDES
layersof covalently bondedsulfur, D will be an average of the covalent, C and close-packedor tetrahedral, I interlayer spacings,weightedasto the relative number of each (see,for saamplelFig. l). As
noted by Goble (1981), planes with spacingscorrespondingto R and D are readily identifiable in the
copper sulfides; theseare listed in Table 4 and shown
as functions of compgqition in Figure 4. The ideal
relationship,D = 2R.l2A,is also shown in Figure 4.
For spionkopite and geerite, the compositions
Cu1.a6S
and Cu,.6oSbetter fit the data of Figure 4
than the compositions Cu1.r2Sand Cu1.53S
determined from the microprobe data of Goble & Smith
(1973),Goble (1980)and Goble& Robinson(1980).
DigeniteD and djurleite R valuesare anomalouswith
respectto the data of Figure 4.
Figure 4 confirms that geerite has approximate
close-packingof sulfur atoms,whereasyarrowite and
spionkopite have structures with a combination of
close-packing and covalent bonding of the sulfur
atoms. In Table 5 the spacingbetweenclose-packed
layers,D' = 2R .12A,has beencalculatedfrom the
R values of Table 4 and combined with the spacing
betweenlayqrs of covalently bonded sulfur in covelline, 2.071 A @vans& Konnert 1976), in order to
determine the number of eachtype of layer parallel
to the c axesof yarrowite and spionkopite. Comparable data are presentedfor covelline, geeriteand anilite. The geerite21d anilifs data are consistentwith
pseudocubicunit-cells containing three and six layers
of close-packedsulfur, respectively; the yarrowite
and spionkopite data are consistent with a number
of different combinations of covalently bonded and
close-packedlayers correspondingto different unitcell contents.
Becauseof the small sample-size,the presenceof
impurities and the scarcity of yarrowite and
spionkopite, no attempt was made to measuretheir
density. Instead, the composition yersardensityrelationships for known copper sulfides shown in Table
5 and Figure 5 wereusedto determinethe most probable densityof yarrowite and spionkopite.Compositions of Cu1.,2Sand Cu132Swere used, as determined by Goble & Smith (1973)and confirmed by
Goble (1980). A spionkopite composition of
Cu1.asS,
consistentwith the data of Figure 4, was
also used.For spionkopite,the data of Table 5 and
Figure 5 are consistentwith a unit-cell content of 14
Cu,.rr_,.*S;for yarrowite, cell contentsof either 24
Cus.12S
or 25 Cu1.12S
are acceptable(although 24
Cu1.12Sseemsmore likely), depending upon the
choice of the density-compositionrelationship in
Figure 5.
The difficulty in the choice of a unit-cell content
and density for yarrowite was resolved by examining the relationship betweenratios of the differently
bonded types of layers (close-packedor covalently
boqded) and composition. In those copper sulfides
D (A)
R6= 1.860.0.058(Cu:S),'
--2-;lg-z-?
;iJ_
o
t
R (A)
,,
t
vfui
-\,
'--'l'
R,=1.850.0.036(Cu:s)
I
1.0 1.2
ti,, '."1r"
1.8 2.0
Frc. 4. The relationship(A) betweenaveragedistanceD
between
sulfurlayersandcompositionand@)between
radiusR of sulfur atomswithin sulfurlayersandcompositionfor thecoppersullides(afterGoblel98l). Open
circlesfor spionkopiteand geeriteindicateanalyzed
compositions(Cur.:zS,Cu1.53S);
open circlesfor
digenite(Cu1.6S)
indicatetwo possible
distances;
open
circlesfor djurleiteindicatetwo possiblecompositions
(Cu1.e3S,
Cur.c7).Correlationswere determinedby
by opencirclc exceptthose
omittingall datarepresented
for digenite,whichwereaveraged.
The dashedline in
B represents
the equationderivedin A if ideal closepackingof sulfur atomsis present.
with lessthan 1.75 copper atoms per sulfur atom,
there is an increasingdegreeof developmentof covalent sulfur-sulfur bonding with loss of copper, as
shownby the data of Table 5. Thesedata wereconvertedto aratio of thenumber of interlayersof covalently bondedsulfur to the number of close-packed
or tetrahedrally co-ordinated interlayers, C/7, and
plotted as a function of composition in Figure 6. For
spionkopitea C/Tvalue of 0.167,correspondingto
2 covalent and 12 tetrahedral interlayers in the cell,
is consistentwith the data; for yanowite, of the three
possibleC/T values,only 0.412, correspondingto
7 covalent and 17 tetrahedral interlayers, is consis-
66
THE CANADIAN MINERALOGISI
TABLT 5. MSSIBLE NUI.IBERS
OF COVALEIIY BONDED
SULRJRLAYERSAI{D
CLOSE-PACKED
SULFUR
LAYERSIlI ONEHEIAGOMLUNII CELLOF
STIECTEDCOPPER
SI'LFIDES
covell lle
lamrlte
uoor{i)
D' (A)
16.341
67.26
3.098
3.101
splonkoplte 4t.429
geer'lte
anll lte
dlgenlt€
dJurlelte
chalcrclte
9.37
19.24
3.119
3.132
3.189
nC + nI
zc+ 47
lC { 217
4Cr 197
7CI I7f
10cr l5T
2C1 l2'l
5C+ 107
8c+87
0c+ 3T
0c+67
o*r.(i) '
67.L9
67.20
67.21
67.23
41.57
41.55
4t.52
9.40
19.14
22
23
24
25
14
15
16
3
6
0.
i;i*jj
4.68
4.48
4.69
4.89
5.09
5.49/5.74
5.8/6.12
3.42/5.61
5.63/5.71
5.76/5.82a
5.79
9ob;: obseryeda cell dlrensloni geerlte and anlllte cells ,ere converted
b,thelr hexagonalequtyalents. R: observedrad.lus of sulfur atons wlthln
sulfur layerslU':
colculated dlstsnce betreen lryers of close-Dacked
sulfur (" 2Rr'2l3i"R.frm Table 4). C: layers of covalenily bond;d sulfuri
spacing ls 2.071 A (Evanst Konnert 1976). T: layers of cl;se-Dacked
Sulfuri spoclng ls Dr A. nC + eT: n@ber of C and T lavers ln'one e
'lengthi
other values of n lead to nonlntegral values oia. o.,t.:
calculoted-d cell dimnslol. Z: nmber of suliur atom in lexagon'ii"unii-ceit;
the a' - a/6. 3.827 A subcell of splonkoplte ls used. Deislty is calculated frcn unit-cell parareteE. Densltles of splonkopjte apfor
Cu1.32S/Cu1.asS.Densitles of geerlte are for Cur_crSTCurrnS. Data
sources are as in Table 4 ercept for dJurlelte (at;-iaken-lr6m rakeda at
a/. (1967b1.
olss oss
pt 0./.
9le
-ot t>o
0.3
:l:
atr
EI;0.2
o23S
EE
014S
5+0.1
clo
olq
Els
>to
ol
ot
I
o22S
0.0
1.2
1.tl
Cu:S rotio
1.6
Ftc. 6. Ratio between the number of layers of covalently
bondedsulfur to the number of close-packedor tetrahedral sulfur layers (ionically bonded) as a function of
composition. Different points shown for yarrowite, spi
onkopite and geeriterepresentdifferent possiblestructures and compositions.
5.8
GPtss
TABLE6. AVERAGE
DISTNCE BfllEEN sU.FUR LAYERS,D, ANDMDIUS OF
SIJI.FUR
ATOMS
HITHIN SOFUR LAYERS,R, IN COPPER-IRON
SULFIDES
{/
56
oineral
E
-u
;'|5'4
sllfur
cubanlte
chalcopyr'lte
haycocklte
talnakhlte
@lh@klte
ldalte
'idalte ?
bonlte
6Pts
fic s.z
(u
cu:s
Fe:s
0.0
0.0
0.33 0.667
0.5
0.5
0.5
0.625
0.55 0.55
0.5625 0.5625
0.833 0.167
0.845 0.155
I.25
0.25
D (i)
hkr
R d)
2.048
3.12
3.03
3.07
3.06
3.07
2,82
2,792
3.18
calc
002
lI2
226
222
221
006
0U
224
1.856
1.867
1.865
1.889
1.874
1.87',t
1.890
1.887
1.937
data
$urce
calc
123,330
220
440
4N
4&
uZ
l',lo
440,408
1,2
3
3
4
5
4
6
7
3
T'
The value of D for sulfur ls tlE average covalent S-S dlstane deternlred tun the strocture of o.thorhotrblc sulfur.
The value of R for
sulfur ls half the mlnlmm lntemolecular dlstance of Ab.ah@ (1955)
scaled to allow for the revlsed cell-parileteB
ol cooper et al.(196x).
olta sources: (1) lbrahms (1955)i (2) Cooperet al. (1961)i (3) Berry
& Tlmpson (1962); (a) Cabri & Hol1 (1972); (5) Hiller & Prcbsthaln
(1956); (6) Frenzel (1959)i (7) Yund (1963).
5.0
oY%rs
1.0
1.2
1.t,
1.6
Cu:Srotio
1.8
2.0
Ftc. 5. Calculated density of the copper sulfides as a function of composition,Filled circlesrepresentvaluescalculatedfrom known structures;open circlesrepresent
possibledensitiesfor yarrowite and spionkopite. Different points shown for a single mineral represent different possiblecompositionsfor this mineral. The two
curvesrepresentthe range fo densitiesto be expected.
tent with the data. Once again, compositions of
Cu1.a6Sand Cu1.66Sfor spionkopite and geerite better fit the data than do the analyzed compositions
of Culj2s and Cu1.sS.
The crystal-structure - composition relationships
shown in Figure 4 can be extendedto include sulfur
and copper-iron sulfides,as shown in Table 6 and
Figure 7. In Figure 7a the interlayer distance, for
copper-iron sulfides,is plotted as a function of the
ratio of metal (Cu + Fe) to sulfur. The linesplotted
are for different ratios of copper to total metal and
satisfy the equation: D = 2.O63+ 0.654
(Cu:S)+ 1.183@e:S),R2= 0.993.In Figure7b the
ionic radius R of sulfur for the samecopper-iron
sulfides is shown as a function of metal-to-sulfur
ratio. Each copper-to-metalratio is representedby
three straight-line segments.The central high-slope
segment o!_each line represents the equation
R: D/Q V%) plotted for the valuesof D in Figure
7a, and was used to determine whether a given sulfide belongs to the "low-metal" (eft) or "high-
CRYSTAL STRUCTURE OF THE COPPER SULFIDES
67
3./,
32
30
J8
:s
o2.6
2.1
22
02
0.1
0.6
08
1.0 12
(Cu.Fe):S
1A
16
t8
1.98
1.96
29
Rl = 1.857.0.039(Cu:5)- 0.020(Fe:S)
1.0(r)
Rh=1.856.
0060(Cu:S)
" 0.023(Fe:5)
R =Dr(2lm)
0a3(4
1.91
0.5(.)
0.33(+)
_1.92
:g
Et.9o
0.0
1.88
1.86
1.81t
0.0
{-------q2
0.1
06
0.8 1.0 12
(Cu'Fe):S
1!
16
18
2p
Ftc. 7. The relationship (A) betweenaveragedistanceD betweensulfur layers and
compositionand (B) betweenradius R of sulfur atoms within sulfur layersand
compositionfor the copperand copper-iron sulfides.Valuesof the Cu,z(Cu+ Fe)
ratio represented
are 1.0(-.-),0.S3
(-4. .),0.5 (-+),0.33
(..+..) and
0 (-). The open diamond in B representsa Cu,/(Cu+Fe) value of 0.44,buta
separateset of curvesfor this value is not included; this point is obscuredby a
closeddiamond in A. In B, each group of minerals with a singlevalue of the
Cu,/(Cu + Fe) ratio is representedby tlree straight-line segmpqts;the middle, highslopesegmentrepresentsthe ideal relationshiF,Rc: D/2,JrA, with D taken from
A; the high-Cu (right-hand) segment represenrsthe calculated relationship
Ra: 1.856+ 0.060 (Cu:S)+ 0.023 (Fe:S); rhe low-Cu (efr-hand) segment
representsthe calculatedrelationshipRr : 1.857+ 0.039 (Cu:S) - 0,020 (Fe:S).
metal" (right) eroup of sulfides. Approximate equations usedfor the low-metaland high-metalcopperiron sulfidesare: R1= 1.857+ 0.039(Cu:S) - 0.020
( F e : S ) , R 2 : 0 . 9 9 2 , a n d R a : 1 . 8 5 6+ 0 . 0 6 0
(Cu:S)+ 0.0234 (Fe:S), R2:0.999, respectively.
The positions of the lines shown are more tenuous
than in Figure 7a becauseof the possibility of a sulfide having a behavior similar to that of high-Cu sui.
fides (anilite to chalcocite)or low-Cu sulfides(coveiline to geerite).
68
THE CANADIAN MINERALOGIST
A,COVELUNE
"--.-....----.L-'F
\ -\ O
,J
aq
=.4
€>
/'
flc
\
/a
$"/ e
/fi
F^$
-ua
ca
( /c
\*6
FIc. 8. /20/Pattersonprojectionsfor covelline,yarrowiteand spionkopite.Peak positions are indicated by filled circles.
In Figure 7, an increasein iron contentresultsin
an increasein D but a decreasein R. This is due td
the presenceof iron in the structuresinhibiting the
formation of covalentS-S layers(1.e.,covellineand
chalcopyriteboth havea metal-to-sulfur ratio of one,
but only covelline has layers of covalent sulfur).
BecauseD is an averagespacingand doesnot include
any of the small covalenti^nterlayerdistancesin the
copper-ironsulfides(- 2 A for a covalentinterlayer
as opposedto = 3 A for a tetrahedralinterlayer),
u
an increasein iron content increasesthe averagespaY
cing of interlayers.Also, the lack of covalentlayers
U
resultsin fewer metal atoms, on average,per tetraoU
hedral interlayerin the copper-iron sulfidesthan in
the correspondingcopper sulfides, and a decrease
in R. As an example,covellineand chalcopyriteboth
u
E
have a metal-to-sulfur ratio of one. D for chalinterlayers
copyrite is the averageof six tetraJnedral
..ANtLIIE"
of approximately3 A each,or 3 A; D for covelline
is the average oj four tetrahedral interlayers of
approximately 3 A eqchand two covalentinterlayers
of approximately2 A each,or 2.7 A. Similarly,in
chalcopyrite there is one metal atom for eachsulfur
or one per tetrahedralinterlayer, whereasin covel0
2
1
6
8,(A)10 12 14 16 l8 20 line, there are six metal atoms spreadthrough four
tetrahedral interlayers or one and one-half per tetra=
Ftc. 9. Pattersonsectionsalong x: 0,./ 0 for coveline, hedral interlayer. This increasesthe S-S distanceand,
yarrowite, spionkopite,sphaleriteand "anilite". Lines therefore,the radipsof sulfur R from 1.80A in chalindicate the interatomic distancesof Table 7.
copyrite to 1.90 A covelline.
F
/lL
CRYSTAL STRUCTURE OF THE COPPER SULFIDES
69
It is interestingto note that the minerals shown
in Figure 7b tend to clusteron or near points at which
the high-slopeR*. Iines or extensionsof the R"d"
lines cut the observedR1and R7,lines for the various metal-to-sulfur ratios, evenif the various lines
havedifferent valuesof the ratio Cu:(Cu + Fe) [i.e.,
B.YARROWITE
idaite lies at the point where the R.4. line for a
Cul(Cu + Fe) value of 0.33 cuts the R, line for a
Cu/(Cu + Fe) value of 0.331.These presumably
representparticularly stable structural arrangements
in the copper-iron sulfides.It is also interestingto
note that the chalcopyrite,mooihoekite, haycock- UJ C.SPIONKOPITE
ite, talnakhite group of mineralsrepresentsa series I
extending along a single Rcal" line at Y
Cul(Cu + Fe) :0.5 (haycockite is actually on a uL
slightly different line). A secondseriesextendsfrom u
:
anilite and digenite to geerite.L. Whiteside (pers.
comm. 1983)has observedfive intermediatestruc- trl
E
tures in a leachingstudy of membersof this series.
In Figures4 andT, the spacingsR and D represent
the radius of sulfur atoms and the averagespacing
betweensulfur layersin the copperand copper-iron
sulfides,respectively.For the coppersulfidesin the
composition ranges Cul.e_,.6S
and Cur.rr_2.6S,
R
would appear to vary continuously. However,
although not representedin this way in the figures,
D must vary in a stepwisefashion sinceit depends
partly upon the number of times a constant quanI -10 12 11 16 l8 20
0
2 4 6
tity, the spaqingof layersof covalentlybondedsulz (A)
fur (= 2.07A) is averagedwith a variablequantity,
sectionsalongx = a/3, y = 2a/3 for
2R l2A. A similar relationship would apply to the FIc. 10. Patterson
yarrowite,spionkopite,
sphalerite
covelline,
and"anilvarious compositionrangesshown for copper-iron
ite'' . Linesindicatetheinteratomicdistances
of Table7.
sulfidesin Figure 7. Theiefore, for eachmineral in
Figures4 and7, D will be nearly constant,particularly becauseof the limited solid-solutionshownby of sphalerite,which are also presentedin Figures9
most copper and copper-iron sulfides.
and 10. Representativeinteratomic distancesfrom
Iron sulfide data are not shown in Table 6 and the covelline,sphaleriteand "anilite" structuresof
Figure 7. Both pyrite and pyrrhotite have octahedral Figure I are listed in Table 7 and indicated in Figures
Fe co-ordination and do not fit the data presented. 9 and 10.The sphaleriteand "anilitd" distanceshave
TheoreticalFeSin the sphaleritestructureis consis- beenscaledto the covellinecell and are therefore distent with the data of Figure 7a but not 7b.
placedslightly from the positions of the Patterson
peaks.
Pqtterson synthesesand space-group determination
Severalfeaturesare immediatelyapparenton the
yarrowite, spionkopite, covelline, sphalerite and
Pattersonprojectionson (010)for yarrowite and "anilite" one-dimensionalsyntheses:
spionkopite are shown in Figures 8b and c (space a) The Pattersonsynthesesof yarrowite and spigroupBml); filled circlesrepresentPattersonpeaks. onkopite are, in general,intermediatein form with
A similar projection for covellinepreparedfrom the respectto the covellineand "anilite" syntheses.
This
data of Berry (1954)is shown in Figure 8a. One- is to be expectedbecausetheseminerals are interdimensionalPattersonsynthesespreparedfor lines mediate in the alteration sequenceanilite - spionthroughx: 0, a/3 and?-a/3for theyarrowite,spion- kopite - yarrowite* covelline and presumably
kopite, covellineldata from Berry (1954)]and "ideal- representstructuresintermediateto those of anilite
ized" anilite unit-cells are shown in Figures9 (x = 0), and covelline.However,the Pattersonsyntheses
for
l0 (x : a/3) and I I (x = 2a/3), Becauseof a lack of yarrowite and spionkopite more closely resemble
reliable data, Pattersonsynthesescould not be pre- those of covellinethan those of "anilite". Patterpared for geerite.However,the strong resemblance sonslnthesesof yarrowite closelyresemblethoseof
of the geeriteand sphaleriteX-ray patternssuggests covelline,whereasspionkopitesynthesesmore closely
that the Pattersonsyntheseswould resemblethose resemblethose of sphalerite.
70
THE CANADIAN MINERALOGIST
A.COVELUNE
B.YARROWTE
C.SPIONKOPITE
F
(,
U
Y
tl
D.SPHALERIIE (:seite)
u
u
E
E:ANIUTE"
0
2
1
6
8 .10
z (A)
12
11
16
t8
20
FIo. 11. Patterson sections along r = 2a/3, y = a/3 for
covelline, yarrowite, spionkopite, sphalerite and
"anilite".
TABLE7. OISTAI{CES
BFmEEN
ATOl'lS
IN THEcOvELtINE,SPHALER]TE
A{D'NILI'TE' S1RUCTURES
nJneral
(E)
distance befreen atons along z-*t.
atms
Lx'Af - ol3'2a/3
Ar,Ay, " 0,0
atons
2 . 0 7( : l C )
!c-sc
:.'lsr..
Ai'ss.
i:ii
LzrCi-.
5c-5c
!c:sc
Cu
Cu-S
sphale|ite
"anilite"
s-d'cu
5.d'c,t
""Cu-LuCu
5.88
6.10
8.t7
8.17
2.2g
2.2g
4.58
s_tinc,
0.00
s-ducu
0.76
s-<
l-u5
fuiu-ducu
"cu-s
ircu-s
5-S
Lttu-Luu
3.05
5.34
s--atcu
Lrcu-i.i.nc!
Sc-z,Cu
s--s
irci-iucu
S-:S
s:-1ucu
!i ",Cu
s.-zocu
aocu_arc!
5-s
S-",cq
Lrc!-Lrcu
0.76
2.29
2.83
3 . 0 5( = l T )
3.60
5.12
5.34
5,8a
7.41
g. 13
8.17
0.76
3.05
3.05
s.34
7.62
iiicu ls @pper ln trlangular coordinat'lon.
ircu ls coppe|in tetrahedral coordlnation.
Sc ls covalently bondedsulfur.
S i s l o n l c a l l y b o n d e ds u l f u r .
itcu-s
may refer
The ordJr of ltms l4-.aton palrs -1g arblt.ary (i.e.,
to both distances ""Cu-S and S-""Cu).
are based upon the
TtE dlstances listed for sphalerlte and "allllte"
,tcu-s
S-s and
dlstances of covelline (1.e., are mt to the sue
scale as the unlt cells for these nlnerals).
Thls result! in
negatlve dlsplacments of these dJstances frm the Patterson peaks
'ln
Flgures 5 and 6.
b) Sets of pseudomirror^planes ile present at
approxir4ately16.8and 8.4 A for yarrowiteand 17.6
and 8.8 A for spionkppite.Thesereflectthe presence
of the I 6.8 and I 7.6 A subcellsnotedby Goble(1980)
and puggestpossibleadditignal subcellsat 8.4 and
8.8 A. The 16.8and 17.6A subcellsshow a closp
in peak positionswith the 16.36A
correspondence
unit-cell of covellineand explain the application of
the covelline unit-cell to the bloubleibender covellines by earlier workers. A similar set of pseudomirror planesexistson the Pattersoq synthesesof
"anilite", representingthe basic 5.5 A cubic closepacked subcell.
c) The strongpeakat a z of 8.210 8.8 A Q = c/2
for covelline)is shifted somewhatfrom x = a/3 in
the covellinesynthesisto x: 0 in the yarrowite and
The shift is more pronounced
spionkopitesyntheses.
in the spionkopite than in the yarrowite syntheses
and is further developedin the "anilite" syntheses.
d) The Patterson synthesesof yarrowite and spionkopite show small peaks at x:a/3, z:0, correspondingto triangularly bondedcopperatoms. The
small sizeof thesepeaksand the lack of suchpeaks
on P6/mmm Patterson maps indicate that space
groups having equivalentpositionswith x differing
by a/3 ard zequal(Hlm, P312,P3lm) arenot possiblefor theseminerals.Therefore,the spacegroup
for yarrowiteand spionkopitemust be oneof Hml,
Hml or P321.
e) The peak at x = 0; z = 4.6 A on the Patterson
synthesescorrespondsto the distancebetweentwo
copper atoms occupying apex-sharingcopper-sulfur
tetrahedra(i.e.,iucu-iucu in covelline).It is moderately strong in covelline,very strong in "anilite",
but weak in both yarrowite and spionkopite. This
suggeststhat in yarrowite and spionkopite the
occupiedcopper-sulfur tetrahedra,rather than facing alternatelyup and down along c as in covelline
and "anilite" (seeFig. l), face either up or down
along c in a given region of the cell.
f) Thereis a generalbroadeningof peaksin the Patof both yarrowite and spionkopite,
tersonsyntheses
suggestingthat there may be considerabledisplacement of copper atoms from the ideal tetrahedral and
triangular co-ordination polyhedra found in covelline and in the idealized"anilite" structure of Figure
l. This will probably be reflected in statistical
occupancyof the four triangularly co-ordinatedsites
surroundinga given tetrahedrallyco-ordinatedsite
in the structure.
Relationship between structure qnd bonding
Structureshavebeenproposedfor covelline,anilite, digenite,djurleite and chalcocite.In the covelline structure (Fig. l), Evans& Konnert (197Qdetermined copper to be in tetrahedral (4 sites) and
triangular (2 sites) co-ordination, with Cu-S dis-
7l
CRYSTAL STRUCTURE OF THE COPPER SULFIDES
tancesof 2.31 and2,l9 A, respectively.In the anilite structure (approximated in Fig. l), Koto &
Morimoto (1970)found copper in distorted tetrahedral (8 sites)and triangular (20sites)co-ordinatiory
with Cu-S distancesvaryinC from 2.28 to 2.52 $
(weighted average 2.37^L) and 2.2.4 to 2.35 A
(weightedaverage2.30A), respectively.
Of the 112
possiblebondsin the tetrahedralco-ordinationpolyhedrq 84 clustercloselyaround a Cu-S distanceof
2.30A, with therem*inderhavingdistances
of 2.52
A (8 bonds), 2.94 A (8 bonds), arLd3.22 L 62
bonds). In the structure proposed for metastable
digenite (Frg. l) by Morimoto & Kullerud (1963),
copper atoms are in distorted tetrahedral coordination, with copper atoms statistically displaced
toward the triangular facesof the tetrahedra.Cu-S
distancesare not given by the authors but, by analogy with the relatedstructureof metastablebornire
(Morimoto 1964),the averagedistancefrom the copper atom to the thrye closestatoms of sulfur can be
estimatedas 2.29 A, whereasthe averagedirlance
from the fourth atom of sulfur would be 2.74A,.In
the djurleite and chalcocitestructures,Evans(1981)
determinedthat the copperatomsweremainly in distorted triangularco-ordinatjon,with Cu-S {istances
varyingfrom 2.18to 2.90A (averageZ.3l A). Two
copper atoms in chalcociteand one in djurleite have
or approachlinear two-fold co-ordigation,with CuS distancesof approximately2.2 A.
Calculatedand observedCu-S bond lengthsfor
the copper sulfide minerals are presentedin Table
8. Observe{ bondJengthsclustef at approximately
2.2 and2.3 A. Comparisonwith the calculatedbondlengthsin Table 8 showsthat yarrowite, spionkopite
and geerite will all readily accommodatecopper
atoms in both triangular and tetrahedral coordination without sienificantly distorting thesesites.
Assuming that the differencein size of the copper
atoms in thesesitesreflects a difference in charge
(l'.e., Cu+ being the larger and Cu2+ the smaller
ion), it may be possibleto predict the relativedistribution of copper atoms betweenthe two types of
sites.Whereasstudiessuchasthoseof Tossell(1978)
and Vaughan & Tossell (1980) show that such a
bonding model is grosslyoversimplified,it may be
used as a first approximation in predicting coordination.
If sulfur is regardedas having a chargeof -2, the
covalently bonded 52 pair in covellinea chargeof
-2, the tetrahedrally bonded Cu in covellinea charge
of + l, and the triangularly bondedCu in covelline
a chargeof +2, one can make the following empirical observationsusing an ionic model (whetheror
not the reducedCu-S distahcein triangularly bonded
Cu is due to Cu* bondedto S- rather than to Cu2+
bonded to S2-,as suggestedby Folmer & Jellinek
(1980), is immaterial; the result is the same).The
IABLE 8.
nlneral
avelllne
yarMlte
splonkop
ite
ger'lte
mll.lte
dlgenlte
djurlelte
chalc@lte
CALCULATDANDOBSERVED
BOND.LA{6IHSIN COPPER
SULFIDES
iil7,,_e
(olcul-aic-a, 8)
2.'191
2.193
2.205
2,215
2.267*
2.262- 2.274*
2.255- 2.3.9,*
2.280- 2.352*
iv",,_.
^ averaqe Cu-s
(catiirlaiea, X) (olseivea, X)
2.323
2,326
2.339
z.Ug
Z,cBA,
2.399- 2.412*
2.462
2.477
data
source
2 . 1 9 ,2 . 3 1
2.{,2,31
2.29
2.2' 2.31
2,2,2.31
2
3,4
5
5
Bond lengths are calculated for ideal closFpacked structures.
*For anlllte the 'ld@llzed" cublc close-packed cell is used;
varlatlons in the dlgenlte data reflect dlfferent data sources.
warlations
and chalcoclte data reflect differences
ln the djurleite
ln locatlon and shape of tie oordlnation polyhedra (parallel or
obllque to the close-packed layers.
Data sources: (l) Evans & Konnert (1976); (2) Koto & t{orlrcto (1970);
(3) l'lorlmto & Kullerud (1963)i (a) Horlmto (1964); (5) Evans (1981).
superscriptson the copper ions refer to the coordination number:
a) The formula of covelline can be written as
(tcu+)4(',Cu2*)r(Sr),r(S,-)r; t'cu-s -2.32 A and
'tu-S - 2.19 A, Overall charge-balanceis maintained; chargebalancebetweenthe close-packedsulfur layersis also maintained, as shown in Figure l2a.
b) The formula of chalcocite.panbe written as
iiiCu-S - 231 L. overall charge(tiCu+)re2(S2-)n;'
balance and charge balance betweenthe layers is
maintainedas shown in Figure l2b (modified after
Evansl98l).
c) The formula of djurleite can be written
for cul.eoS or as
as (it,Cu+)601iigrz+)r(s2-)32
*
*
Evans (l 979)
1,tu lur1ttcu2)z(52)n for Cu1.e7S.
reported only 62 copper atoms in the structure, of
which one, Cu{62),is in linear two-fold co-ordination
(tu-S - 2.2 A); a second,Cu(13),would appearto
approachlinear co-ordination. The remainder of the
copper ions is approximately in trianeular three-fold
co-ordination (ttcu-S - 2.3 A). As shown in Figure
l2c (modified after Evans l98l), whether or not
overall charge-balanceand a balance of charge
betweenthe layersare maintainedwould dependon
the location of a secondcupric ion or on the location of the "missing" cuprous ion in Cu6S32.
d) Distortions in tetrahedrally co-ordinated sitesin
anilite and displacements from tetrahedrally coordinated sitesin metastabledigenitereflect the fact
that neither tetrahedral nor triangular co-ordination
polyhedrain thesemineralsfit our model. Instead,
both Cu+ and Cu2* tend to be in intermediatepositions.
e) Figure 4 showsthat there is a basic difference
betweencoppersulfideswith Cu:S > 1.75and those
with Cu:S < 1.60. This is reflected in the coordination number of cuprous and cupric ions.
Structurally, yarrowite, spionkopite, and geeritewill
approximate the behavior of covelline and contain
cuprousions in tetrahedrallyco-ordinatedsitesand
cupric ions in triangularly co-ordinatedsites.Also,
72
THE CANADIAN MINERALOGIST
r
tu-2
rrl
i"-r
l^
cr1
)
i"-z
91
si
Cs2
5
Cu{
c!-1
s
&-2
Cu-2
5
c(
&{
92
Cu-3
Cu?
tu-l
"64$:5 - -6-.;:;u*,,
3Yi
A.COVELLINE
C)
ovr
3it-)
o&o3#
-
Cu-l
C.DJURLEIIE
l-llPil1n
.uL
l-rt Nr4ti
.3L
t^
.%
llt lni4|(
.78
l^
.7tg
_1
Fl
''
1
t0
!1il.] 11
.1
l0
-11
.36
ffi)
om-
q2
AJ
D.YARROWITE
D.YARROWITE
E.SPIONKOFNE
F.OEERITE
F.
OEERITE
Frc. 12. Ionic bonding in covelline, low chalcocite(Evans 1981),djurleite @vans
l98l), yarrowite, spionkopiteand geerite.Numberswithin the covellinestructure
in A representionic charges;in other structuresthey representsite occupancies
other than one. Numbersto the right of eachstructurerepresentcharges;anows
indicatethe amount of chargeabove(f) and below (l) the ion.
atoms in the structuresof yarrowite and spionkopite are, like thosein covelline,constrainedto atomic
g4rlte
ylrelts
spJonkopite
@velllne
positionswith x: 0, o/3,2o/3 by peakpositionson
Pattersonsyntheses.
cu1.32s cur.s3s
Cul.l2S
analyzedconposltion: tot.ooS
structuralcmposltlon'-The formula of yarrowite can be writtpn as
f)
cur.60-r.6rs
(fm FJgs. 6'9):
c'l.36-r.4os
Cut.]lS
Crt-ooS
(,cu*)r(,iCu'*)r(sttr(stl10; 'vcu-s - 2.33A and
rhmbohedral
huagonal
iExagonal
heFgonsl
crystdl syst4r
rttcu-S=2.19 A. To maintain charge balance
RSr?
PSnt, P32l
P6y'@c
space
sroupr
or P301
Tl,rHi
betweenthe sulfur layers, a distribution of copper
I
@ t l d i m n s l o n s : a . 3 . 7 $ 8 8 a . 3 . e O 0 E a - 22.s628 aa :"1 15.77
3056'
cE4l.429I
c"16.34lX c"67,264
atomssuchas in Figure l2d is required.Within this
c!8sg
c'rg.s\q
hnSzq
Cus
fomla:
generalmodel, sulfur atomscan be shifted to many
z
r
2"36
7'1
2"6
unlicell @ntent:
possiblepositionsas long as the symmetryrequireg/q3
g/m3
5.61
q/cti3
5.33
4.91
+.oe E/o3
catdlated d€nsliy:
nunber of sulfut
mentsof the spacegroup are maintainedand seven
'14
5
24
6
layeB in unft celt:
layersof covalentlybondedsulfur are retained.Cu
nwber of covalently'layers
bondedsulfur
atomsin triangularly co-ordinatedsitescanbe shifted
7
20
2
ln unlt cell:
perpendicularto c, and Cu atoms in tetrahedrally
avefage n@bet of
@pper a&ns pea
co-ordinatedsitescan be shiftedwithin the two sites
close-Dacked
1.59-1.63 1.53-1.60
1.58
1.50
sllfur laFr:
in any layer.
The formula of spionkopite can be written
Data are fw Pottet & Evans (1976), coble a smith (1973)' 0ob1e (1980)' and
e)
Goble& Roblnson(1980). The denslty of splonkoplte is ronglv repoded
iucu-s as 36^('ucu*)rr(t'icu2*)c.s(FJ2-r(S2-)'oi
as 5.13 g/@3 by coble (1980); thls ls th value for the analyzed@mosltlon, Cll.32S.
234 A and 'tu-S - 2,20 A. To maintain charge
TABLE 9.
SPIONrcPII! AilD CEERITE
DATAFORCOVEIIIIIS.YARROIITTE,
'IRTJCTUML
CRYSTAL STRUCTURE OF THE COPPER SULFIDES
73
balancebetweenthe sulfur layers,a distribution of
copperatomsfor the a' subcellsuchasin Figure 12e
is required.Shifts in the position ofsulfur and copper atoms are possibleas long as the requirements
of symmetry are maintained and two layersof covalently bonded sulfur are retained in the structure.
h) The formula of geerite can be^ written as
(tcu * )6(,:cu2* )r(sr-),;,-,cu-s = 2 3 s x and ttr.S - 2.22A. To maintain chargebalancebetweenthe
sulfur layers,a distribution of copperatomssuchas
is shown in Figure l2f is suggested.This structure
is basedupon that presentedfor metastabledigenite
by Morimoto & Kullerud (1963),with the restrictions
that copperatomsbe locatedonly in undistoftedtriangular and tetrahedralco-ordination polyhedra and
that rather than one out of everyfive Cu-S-Cu sandwicheshaving one empty Cu position, two of five
must be empty.
It is to be expectedthat in eachof thesestructures
(yarrowite, spionkopite,geerite),therewill be some
distortion of the ideal Cu-S triangular and tetrahedral co-ordination polyhedra, as has beennoted
in previously determinedcopper sulfide structures.
The basicstructuraldata for covelline,yarrowite,
spionkopiteand geeriteare summarizedin Table 9.
For each structure, the averagenumber of copper
atomsper tetrahedral layer is calculatedbasedon the Frc. 13. A, B, C, D: Possiblearrangementof layers of
ionically bonded and covalentlybonded sulfur in spiideal compositionas determinedfrom Figures4 and
onkopite. E. Attempted crystal-structuredetermination
6 and structural data. For yarrowile, spionkopite and
of spionkopite;fractionsindicatesiteoccupancy;scatgeerite,this numberapproximates1.60,whereasfor
tering factors for copper were used for all positions.
covellineit is 1.50. This suggeststhat in the tetraF. Possibleinterpretation of the partial crystal-structue
hedral layersbetweenthe layersof covalentlybonded
of E.
sulfur, the structuresofyarrowite, spionkopiteand
geeriteprobablyhavea similar co-ordinationof copper atoms, and that this is somewhatdifferent than
in covelline.
of the 41.4A cellwith atomicpositionsindicatedfor
PARTIAL DETERMINATION
that structure giving the lowest R-value. R for this
OF THE CRYSTAL STNUCTUNE OF SPIONKOPITE
structureis 0.280for observeddata but increasesto
A.404 if unobserved data are included. This was
The numerousmethods of arranging 2 covalent found to be the generalcasefor spionkopite;R could
and 12tetrahedrallayersparallel to the c axis of the readily be reducedto below 0.20 for observeddata,
spionkopite cell may be reducedto four types as but inclusion of unobservedreflections causeda
shown in Figure l3a,b,c,d (assumedspacegxoup sharpincreasein R. For this reason,an attemptwas
IF,ml). All other possiblearrangementsmay be der- made to find the relationship governingthe unobived by shifting the sulfur atomsparallel to the c axis servedreflections.It should be noted that for most
(i.e., by changingthe origin). All possiblepositions of the attemptsto determinethe structure, scatterfor copperin tetrahedralco-ordination are indicated; ing factors for copper were used; sulfur would be
triangularly co-ordinatedsites have been omitted. expectedto show up as Cu with approximately Vz
Numegousattemptsweremade^atsolving the 8.8 and occupancy.Attemptsto changeselectedpositionsof
1?.6A subcellsand the 41,4A cell of spionkopite, copper to sulfur did not result in an improvement
starting with the basicstrucfural arrangementsshown in the R factor. A possibleinterpretation of the strucin Figure 13and assumingthat large areasof the sub- ture in Figure l3e is shownin Figure l3f. The intercellswould resembleeither the covellineor 'Jdeal- pretedstructureis inconsistentwith a centricspaceized anilite" structures(thea' = q/6 = 3.827 Asub- group. It is also missing severalcopper atoms.
cell was used in all attempts at determining the
An examinationof the structurefactors (Table2)
structure). In everycase,splitting of atomic positions showsthat for the spionkopite cell (a' = a/6), the
becamea problem.Figure l3e showsthe bottom half / Miller index for reflectionsof the type ft minus fr
74
"l;"-l"l--.:l
THE CANADIAN MINERALOGIST
045 o
o20
[_] 1__j
8i:
o 4 5 9ro
o20 o
AB
hrin oxis
f
FIc. 14.A. Atomic positionsin the 8.9 A subcellof spionkopitenecessary
to account
for the systematicabsences;fractional occuppnciesare indicatedas percentages.
B. Positjon of Pattersonpeaks for the 8.9 A subcell. C. Structure derived for
the 8.9 A subcell:positions onx = a/3 and:c = 2a/3havethe sameoccupancy.
D. A twiqned-sphaleritesubcellfor comparisonwith C. E, Structurederivedfor
the 35.5A subcell;positionson x: a/3 and x: 2a/3 havethe sameoccupancy.
F. A possibleinterpretationof the structurein E. G. A tqinned-sphaleritesubcell
for comparisonwith E. H. A twinned-sphalerite41.4 A cell for spionkopite.
e q u a l s3 n i s 4 , 7 , 1 1 , 1 4 , 1 8 ,2 1 , 2 5 , 2 9 , 3 2 ^ 3 6 I. f
the cell is re-indexedon the basisof a 35.5 A pseudocell, this index approximates3, 6, 9, 12, 15, 18,
21, 24, 27, 30. The data setre-indexedon this basis
has two setsof extinctions:if I minus k is equal to
3n, then / is not equalto 3n, and if Z minus k is not
equal to 3r, then / is equal to 3n (but / is not equal
to 0). Theseextinctionsrequirethat atomsbe placed
in the cell in the positions0, 0, zi V3,2A,z + tA;
2/t,rA,z, * 2A;r/t,2A,z + 2/z;2/t,
rA,z + rA(frml
spacegroup). The atom at 0, 0, z must havedouble
the weight of the remaining atoms. Theseatomic
positions (with z = 0) are indicated on Figure l4a,
togetherwith peak positionsfor a Pattersonsynthesis
on an 8.9A subcellbasedupon the abovere-indexed
data (Figure l4b). The peak positions on this Patterson map are identical with those of a sphaleritetype $tructureusing the body diagonal as a c axis.
In Figure 14, lessthan full occupancyof the sites
is indicated as a percentage.
o
Various attemptswere made at solving the 8.9 A
re-indexedsubcell of spionkopite using least-squares
refinement and the minimum residual method o.f Ito
(1973).The final structurederivedfor the 8.9 A reindexed subcell is shown in Figure 14c. R for all
reflectionsis 0.292(againscatteringfactors wereused
for copper only). The correspondencewith the
atomic positions derived from consideration of
extinction data is obvious, as is the similarity to a
'jtwinned-sphalerite"structure(Fig. lad). This 8.9
A re-indexedsubcell*u, e"p*d"Jinto ihe 35.5 A
re-indexedcell as shown in Figure l4e. A possible
interpretation is s.lrownin Figure l4f. A "twinnedsphalerite" 35.5A cell is again shown for comparison (Fig. l4g). The interpretedcell shown in Figure
l4f is againinconsistentwith a centricunit-cell and,
75
CRYSTAL STRUCTURE OF THE COPPER SULFIDES
onceagain, severalatoms of copperare missing.The
prediction that there would be fewer apex-sharing
tetrahedrathan in the covellinestructure is shown
by the distributign of copperatoms.All attemptsat
solving the 41.4A cell of spionkopiteusingthesedata
failed. No atomic arrangementcould be derivedthat
would account for the observedsystematicextinctions, afthoughexpansio! would appearto take place
by the insertion of a 6^A segmentbetweenthe two
halves of the 35.5 A re-indexed subcell, such
as is slown in Figure l4h for a "twinned-sphalerite"
41.4A structure.
DISCUSSIoN
In attempting to solve the structure of spionkopite, we are trying to derive a minimum of seventeen independentatomic positions using just 147
observedreflections.If, as is suggestedby the partial structures shown in Figures 13f and l4f, the
structure is acentricrather than centric (Azl rather
than frml), this number would increaseto thirtyfour. The full cell is in fact thirty-six times this large.
In addition, featuressuch as the diffuse nature of
the X-ray patterns,broadeningof peakson Patterson synthesesand splitting of atomic positionsduring structure determinationsall suggestthat Cu is
statistically distributed between the two possible
tetrahedrally co-ordinatedsites of copper between
sulfur layersand among the four possibletriangularly co-ordinatedsites of copper situated around
eachtetrahedrallyco-ordinatedsite. Any attemptat
removing constraintson the x andy atomic positions
during determinationsinvariably lead to splitting of
peak positions in these directions as well as along
z. Given theseobservations,it is extremelydoubtful that the structure of spionkopite can be fully
solved with the currently availabledata.
Most of the problemsthat exist in attemptingto
solvethe spionkopitestructurecan be applied equally
well to the yarrowite structure.The only factor that
might make it more amenableto structuredetermination would be the previousobservationthat large
areasof the cell should strongly resemblethe covelline structure(e.9., Fig. l2d). However, attemptsat
solvingthe spionkopitestructureusingthe structure
of covellineas a model were unsuccessful.
The structure of geeritemay be solvable.Peaks
observedon X-ray patternsare relativelysharp.The
major hindrancein determiningthe structure may
lie in the scarcityand small sizeof natural material.
Experiments such as those conducted by Globe
(1981)may provide a methodfor synthesizinglarger
fragments of geeritefor single-crystalstudies.
ACKNOWLEDGEMENTS
The author thanks Dr. G.W. Robinson for provid-
ing the specimenof geeriteusedin the single-crystal
studies.Discussionswith Dr. J.D. Scott were particularly helpful during the attemptsto solvethe crystal structureof spionkopite.Finally, I thank Mr. L.
Whitesidefor helpful discussionsduring the writing
of this paper and Helen Betenbaughfor tlping the
manuscript.
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