American Mineralogist, Volume 58,pages435-439, 1973
TheGrystalStructureof Parkerite(Ni'Bi,S,)
MrcrnBr E. FrBrr
Departmentol Geology,Uniuersityol WesternOntario, London, Canada
Abstract
Parkerite (N;BLSL) is orthorhombic with a - 5.545(4) A, b = 5.731(3) A, c - 4.052(3\
A, space gtonp Pmam (D:),
Z - 1 The crystal structure, determined on synthetic material,
consists of a C centered arrangement of Bi atoms with the Ni in two non-equivalent positions
octahedrally coordinated to four Bi and two S and juxtaposed across shared octahedral faces
with Ni-Ni distances less than 2.80 A; the Ni(2) site has an occupancy of 0.5. The S is
coordinated to three Ni at the apex of a trigonal pyramid giving Ni-S distancesof 2.02 A and
2.05 A, which are significantly shorter than in other nickel sulfides. The parkerite structure
is shown to be a derivative of the shandite (NilPb,Sr) structure, the essential differences
being the distribution of the Ni atoms about the heavy atoms and the apparent direct coordination of S to the Pb(2) atom in shandite.The short Ni-S distancesin parkerite are related
to a r bonding contribution to these bonds and further crystal chemical analysis of the compound predicts that only four electrons populate the non-bonding d orbitals on each Ni. The
distribution of Ni-Bi and Ni-S bonds readilv accounts for the excellent {010} cleavageof
parkerite.
Introduction
Parkerite (NiBBizS2)occurs in certain arsenidesulphide assemblages
in associationwith other Bi
and Ni phases,suchas nativebismuth,bismuthinite,
niccolite and maucherite.It is an uncommonmineral, havingbeenreportedonly from Insizwa,South
Africa (Scholtz,1936) and three localitiesin Canada-Sudbury, Ontario (Michener and Peacock,
1943), Great Slave Lake, Northwest Territories
(Thompson, 1951) and Cobalt-Gowgandaarea,
Ontario (Petruk, Harris and Stewart, 1969).
The chemical analyses of the specimensfrom
Ontario correspondquite closely to the ideal composition but the Insizwa parkerite contains a significant amountof Pb (9.5 wt percent) substitutingfor
Bi. Parkerite is orthorhombic; the Sudbury material
hasa = 4.03 A, b = 5.53 A, c = 5.73 A, possible
space group Pmm2 (C;,), D^ = 8.4 gm/cm-",
Z = I (Michener and Peacock,1943). The lattice
parametersreported for the Cobalt-Gowgandaparkeriteare a = 4.009A, b = 5.541A, c = 5.749A.
The orientation of the unit cell as reported by earlier workers does not conform to the present convention for orthorhombic cells. Henceforth, in this
article, the conventionalorientation will be adopted;
the earlier orientation is related to it by the transformationmatrix (010/001/100).
Ni3Bi2S2can be synthesizedquite readily, the
product being optically and crystallographically
equivalent to parkerite. As shown by du Preez
(1945), there is extensivesolid solution at the Bi
end of the NigBizSz- NigPb2Szsystem' extending
almost to Ni.rBiPbS2.However, the solid solution of
Bi in the Pb end member is limited to less than 4
mole percentNi3Bi2S2.SyntheticNigPbzSzis equivalent to the natural phase shandite which is rhombohedralwith r = 5.576 A, o = 60o (Peacockand
McAndrew,1950).
ExPerimental
The present study was made on synthetic material rather
than natural material to achieve more rigorous control of
composition and, hopefully, a more suitable crystalline
product. The parkerite was synthesizedby reaction of the
pure elements in a sealed silica glass tube heated for seven
days at 600"C in a horizontal tube furnace and quenched
in water. The commercial Ni sponge was heated at 900"C
in a stream of hydrogen gas before use to remove possible
oxygen contamination. The product of the synthesis was
massive and in the form of a plug. Polished sections show
the development of {111} twin lamellae to be much less
than in the synthetic material examined by Michener and
Peacock, being limited to grains on the margins of the plug.
Preliminary single crystal work on a precession camera
essentially confirmed much of the earlier data in the literature. Parkerite is orthorhombic with a = 5'545(4), b
5.731(3), c - 4.052(3) A; the lattice parameterswere determined by least squares refinement of 12 centered reflections measured in the later, four-circle diffractometer study
43s
4t6
MICHAEL
with Zr-filtered MoKa (I - 0.7107 A) radiation. The systcmatic absences, ftOl with h I 2n (implying hOO with h
/ 2n), are consistent with space grolps P21am (C2r.),
Pma2 (Ct',) artd Pmam (Dfi). These are equivalent to
the systematic absencesreported by Michener and peacock,
althqh
these earlier workers did not recognize the a-glide
comporlent,
Some difficulty was encountered in obtaining a single
crystal suitable for the collection of the intensity data.
Becauseof the high linear absorption coefficient of parkerite
(765.2 cm-'), it was clearly necessaryto use an equidimensional crystal to realize meaningful absorption corrections
on a conventionally-sized crystal, and it was appreciated
that, evcn if this requirement were met, small errors in
dcscribing the crystal shape could result in appreciable
errors in the corrected data set. However, parkerite has
an excellent {010} cleavage so that the dominant habit of
crystals from the crushed plug was tabular. Moreover, the
synthetic parkerite is relatively soft and the crystals bend
very readily through a combination of the {010} cleavage
and {111} fracture. Attempts to prepare single crystal
spheres in a Bond sphere grinder were frustrated because
the crystals cleaved readily on impact with the abrasive.
The probkm was resolved eventually by choosing a small
crystal (calculated volume of 0.31.10-?cms) and mounting
it on the 6-axis to minimize possible errors in the absorp
tion correction.
The X-ray intensity data for the structure analysis were
taken on a Ficker racs 1 four-circle diffractometer system
at the University of Western Ontario. All hkl reflections
utith 2e ( 65' were measured using a scintillation detector, Zr-filtered MoKa (r - 0.7107 A) radiation and the
2a scan technique: 40 second stationary background counts,
peak-basewidths of 2.O" 20 (uncorrected for dispersion)
and a scanningrate of 0.25. per minute. The resulting data
werc pro€€ss€dby a data correction routine which corrected
for background, Lorentz and polarization effects, and absorpti,on, asd asdgnod standard deviations (c) to the corrected
deta basoC m the summed variances of the counting rates
of tb peaks and associatedbackgrounds. Transmission factors for the absorption correction were calculated by the
analytical method of de Meulenaer and Tompa (1965). The
calculated tranemission factors varied from 0.10 for reflection 010 to 0.20 for 280. Each reflection whose intensity
was less than the associatedbackground plus 3,c was given
zero iatensity. The final data list contained 308 reflections
of which 78 were 'unobserved'.
Ctystal Structure f nvestigation
The solution of the crystal structure of parkerite
was initiated by a Pattersonsynthesiswhich showed
quite clearly that the expected two Bi atoms per
unit cell were arrangedapproximatelyon a C centered lattice with some of the Ni content fourcoordinated with it at z = l/2 relative to the Bi.
Using a trial structurebasedon the centrosymmetric
space group Pmam with Bi in the 2e (l/4, y, O;
y = O.75) positions and with the Ni distribured
over the 2b (O, O, l/2) and 2d (0, l/2, l/2)
E. FLEET
positions, an Fo synthesissuggestedan improved
set of initial positions (Table 1): the S is eight
coordinated with Bi and each Ni is octahedrally
coordinated to four Bi and two S. A consequent
valueof the conventionalresidualindex (R) otA.22
and an absenceof alternatepositions on a Fo map
suggestedthat the basic structural features of parkerite had been outlined at this stage.
The structure was refined further by full-matrix,
least-squares
refinementusing program RFINE (L.
Finger,Geophysical
Laboratory,Washington).RFINE
minimizesthe function lw(lFol
lF"l)', where
w = l/o', and calculatesa conventionalresidual
index,I llF l - lF.lll>lF.] and a weightedresidual
index,E w(lF l - lF"l)"/2wE"'1'r".The scattering
curvesfor Ni'- and Bi were taken from Cromer and
Mann (1968) and that for S'z-computedfor a nine
parameterfit from data in the International Tables
for X-ray Crystallography,Vol. IIL The anomalous
dispersioncoefficientsof Cromer (1965) for Ni, Bi
and S were included. Isotropic and anisotropicthermal parameterswere added successivelyto the refinement.However, the isotropic thermal parameter
for the Ni(2) position refined to a negativevalue,
presumablyreflectinglimitations in the data set and,
as a result, it was constrainedto the value of the
thermal parameterfor Ni(1), since the two sites
are quite similar. The refinement,then, was limited
to isotropic parametersfor Ni and anisotropic parametersfor Bi and S and was terminatedwhen the
changesto the positional and anisotropic thermal
parameterswere in the sixth places and the ratios
of the changesin these parametersto the errors in
the parameterswere less than 0.005. The final
values of the conventional and weighted residual
indices for the non-zero intensitiesare 0.096 and
0.104 respectively.The refinedstructurewaschecked
with F6 and Fo-EcFourier maps; no significantresidual peaks were detected.Observedand calculated
structurefactors are given in Table 2, andpositional
and thermal parameters and associatedstandard
deviationsare given in Table 3.
Tenre l.
Initial Positional Parameters for Parkerite
Equipotnt
positio!
Occupancy
Nl (1)
Nr(2)
2b
2e
1.0
0.5
0
Ll4
Bi
2e
r.0
Ll4
S
2f
1.0
Ll4
0
o.25
Ll2
0
0
o.25 LI2
437
CRVSTAL STRUCTURE OF PARKERITE
TesrE 2.
KLF
F
ococ
H=0
0 1 83 92
2 L59 r92
3 72 69
r00 109
5 49 44
6 61 58
I 0 48 50
1 36 46
2 39 38
3 L7 29
4 25 27
5
015
6
0 11
2 0 r22 L23
1 r38 158
2 95 96
3 LO2 Lt6
4 65 59
5 63 69
3 0 41 4L
I 55 36
2 28 33
3 33 23
o20
5 22 72
4 0 137 138
I 62 6L
2 108 tt6
3 s4 48
4 74 75
5 37 32
5 0 25 I8
I
030
2 20 75
3
023
4
09
5
014
6 0 44 43
L 74 77
2 40 38
62 60
32 28
L7 26
386
o23
255
45 48
31 22
42 43
=1
1 0 96 93
I 129 731
2 78 81
3 87 84
4 52 55
5 49 48
6 30 33
2 0 38 23
024
I
Observed aod Calculated Structure Factors
KLF
F
KLF
oc
F
223L94494r
ss553
3
016
50 21 30
4
O tI
L44L6
5
0
9
2 77 26
30 88 87
3 29 12
1 105 103
272754018
3 66 73 6o
7g 77
52
450
s4L44
26868
40 48 31
3 37 30
11531
448r8
2 32 26 jO
22 5
3023LOZ1
42517
222
5
50143019
50 71 71 gO 25 23
L6975
t5044
25663
3 52 57
H=3
44344
6o 42 28
Lo 82 79
1, 23 27
1 106 104
23124
27369
31721371.74
426L74fi49
7O 52 52
5 44 43
| 47 52
20 25 tB
243471019
3394222275
80 35 20
3
0 13
020
1
4
oto
22514
5
O 8
30 77 74
H-2
1 89 88
26265
00131132
3 65 65
1 155 159
4 47 46
2 LLO L02
5 39 40
3118116 4o
38 26
46852!OZ7
5687022922
54 44
Io
3 15 20
150414].915
2 39 35
50 61 63
3302616166
4782025256
5
014
3s051
20r77I87
4 39 40
7 86 77
Go 34 24
2L44r5o
o 24
I
3685923j.22
488923019
5 49 39
1O 4j 47
30 31 31
1 Ll t.1
1
033
24542
2 28 25
80
29 18
31523
15
4r7
5
014
40 78 7r
r 114 110
2696r
38483
KLF
F
0 0 t56 r58
16967
2 130 131
35854
48384
54236
IO 33 29
12828
22624
31820
42r15
5
0 12
20 9L 84
1 113 r13
27772
38587
45648
55656
30 31 28
t3822
22224
326L5
4 L't t6
4 0 101 t01
r5148
28587
34539
46260
50 19 12
L
O22
2010
3018
407
60 36 35
16560
23932
35249
70
0 21
4
L25
2
0t9
KLF
F
3
4
50
016
013
45 50
47 53
44 45
4t 42
27 19
019
20 r7
N1(1)
Nl(2)
s
4454L
t0
25 20
r1918
222r7
3
013
012
4
20 92 97
74646
28184
34039
45859
30
19 13
1017
2
0t2
3
014
40 44 45
65
L67
24240
35253
50 19 1E
8
L26
016
2
60 47 50
3
2 0
I
2
3
0
1
2
0
1
40 43
52 55
39 40
44 43
09
09
08
o7
4L 42
46 49
35 38
014
014
0 06671
r3236
I 11612
2 o4243
15155
Some interatomic distancesand bond angles of
interest are given in Tables 4 and 5 respectively
(the atom identification labels are consistentwith
the usagein Figure 1; atomsmarkedby an asterisk
are located in adjacent unit cells). Although the
single Ni(2) atom is distributedover two equivalent positions,the X-ray diffraction patterns of parkerite show no evidencethat theseatomshave anv
B--
0.92<L3)
0.92(13)
o
o.204(3)
1.0
rl4
o.7423(7)
0
0.79(8)
1.13(10)
1.04(10)
1.0
rl4
0.256(9)
u2
L.2(7)
7.6(1.9)
4.1(1.3)
*Esti@ted
dwiatLons
statdard
last declDal
Placgcited.
of 0.003.
(ln Parentheees)
Thqs' 0.204(3)
lefer
me&s
to
an
tendencyto long rangeorder.The Ni( 1) and Ni(2)
sites are quite similar; both are in octahedralcoordination with four Bi and two S; each of these
coordination octahedra shares four faces so that
interatomic distancesbetween Ni atoms related in
this way are lessthan 2.80 A. The Bi is coordinated
to four Ni(1) atoms, arrangedto one side of it,
and to four of the half-occupiedNi(2) sites.It is
anticipatedthat the Ni(2) siteswould exhibit sholt
range ordering in which most of the Bi atoms would
be coordinatedto two Ni(2) atoms. The average
Ni-Bi bond distance is 2.85 A, which is a little
longer than the bond distance in the alloy Nitsi
(2.71,A, Hiigg and Funke, 1930). The S is coordinatedto two Ni( 1) and to two of the half-occupied
Ni(2) sites so that any specificS atom would be
three coordinated to Ni at the apex of a trigonal
pyramid.
Parkerite is usually classifiedas a sulfosalt since
its chemistry involves a metal atom in combination
with a group V element and S. However, Takduchi
and Sadanaga(1969) have argued that it is the
pres€nceof TSg pyramids (where T is a group V
element) that distinguishesa sulfosaltfrom a sulfide,
and since the present structure determination has
shownthat Bi is not coordinatedto S, parkeritewould
Tesrn 4.
Bond Distancesin Parkerite
olstmee(i)#
Atous*
Discussion of the Structure
Ll2
0
-22
o
Ll4
Sg
57 70
00
18285
26L60
Bt1 (B)
*
1.0
the
H=5
10 59 59
'19
78
|
25353
36158
43940
20 l7 L3
1014
0 Ll
2
30r0
408
30 54 57
L6567
25051
35L52
43938
26 L9
40
1020
222L7
OecuPecy
At@
Pararneters
Refined Positional and Thermal
for Parkerite*
3.
TleLp
N1(1")
- Ni(lr)
- Ni(2r)
- Birt
-Sr
2.772(2)
2 . 7 1 8( 8 )
2.865(2)
2.02(4)
Nl(2r)
-
3.o9(2)
2.64(z',)
2.790(3)
2 . 0 4 8( 8 )
Bil
BL*t
Birr
Sl
*Atm
At@sx
Bir sr
otstance(i)*
Bir
Bi"
sr
s*r
s'r
4.052(3)
3.924(4)
3.45(4)
3.57(4)
3.434(2)
- s,
- sr I
- s*r r
4.052(3)
3.94(5)
4.04(5)
mrked by asterLsks are located ln adjacat
cells.
uLt
*standard
(ir PaEentheses) refer to the
dsiatl.ons
place cited.
last decinal
MICHAEL
438
Tlsrl
5.
E. FLEET
Bond Aneles in Parkerite
arrangementsof the Ni atoms about the heavy
atoms.In both structuressix Ni are coordinatedto
angle
a[gle
Angle*
At@s* foming
At@s* foming
each
heavy atom, but in shanditethe Ni atomsform
- Bt, - Ni(1")
57.9(1)0
Ni(l')
r8o.o(o)
Bix, - N1(1,') - 3i"
- Nr*(1") U7.9(1)
- 3i"
90.o(1)
a
trigonally-distorted
octahedronabout the Pb(l)
- Nr.(2') 121.0(1)
3i,r - Ni(r,,) - 81,, 90.0(1)
- Nr*(2')
- sr
s9.o(1)
87.6(7)
site
and
a
hexagonal
ring
about the Pb(2) site. In
|
- sxr
Ni*(r') - B1' - N1(2") 115.1(3)
92.4(7)
- Ni(t'r) - s*"
180.0(0)
N i ( 1 , , ) - 8 1 , - N 1 * ( 1 t' ) 9 o . o ( 1 )
st
addition
each
S
is
coordinated
to a Pb(2) atom, as
57.5<2'
Ni*(l,') - Btt - Ni(2")
- Bi' - Ni*(2') 180.0(0)
Ni(2')
well
Bi, - Ni(2t) - Bi*r 180.0(0)
as
to
three
Ni.
However.
was not resolvedin
S
- Ni(2,,)
- Bi"
83.6(4)
95.4<4)
.
- s'|
the
81.6(1.6) Ni'(2') - Bi, - N1(2,,) 83.6(4)
original
structure
analysis,
but
it was positioned
Ni(2t 'i) - Bi' - Nr3(2") 167.3(8)
sr*' - }Ii(z') - gi" - 96.4(4)
- s'!
to give Pb-S and Ni-S distancescomparableto the
98.4(1.6)
86.8(2.0)
Ni(1,) - s, - Nt(1t')
Bi,' - Ni(2') - Bi*" 167.3(8)
- Ni(2'|)
- s'|
respectivedata for galenaand millerite.
89.L(2)
83.9(1.2)^
s
'
N
1
(
2
'
)
1
63.2(3.1)Nr(2')
s'
163.2(3.1) Ni(2,)
st
The structure of parkerite requires 18 o bonds
aAt@s @rked by asterisks
celLs.
are located iD adjacent @lt
(12
Ni-Bi and 6 Ni-S) per unit cell. Paramagnetic
*stardard
(in parentheses)
dwiations
refer to the last dectlal
place cited.
data for parkerite,and hencedirect evidencefor the
3d electron configuration of the Ni atoms and the
total
number of valenceelectronsused for bonding,
not be included as a sulfosalton the basis of this
are
not
available,but analysisof certain aspectsof
criterion.
the
structure
does allow a qualitative treatment of
The parkerite structure is a derivative of the
the
bonding.
The outer electron configurationsof
shandite (Ni3Pb2Sz)structure (Peacock and Mcthe
constituent
neutral atoms are Ni - 3d84s2,
Andrew, 1950). Although shanditehas a rhombo- 3s23p+.
Bi6s26p3
andS
hedralunit cell with r = 5.576A, the rhombohedral
angleis 60o and the Pb atoms are arrangedon an
The nearest Ni-S distancesin parkerite 1Z.OZir
ideal C centeredlattice (Fig. 2), essentiallyequivalent to the locationof the Bi in parkerite.The nearest neighbor Ni environmentsare quite similar in
both structures,differing only in the dispositionof
the four Ni(1) neighborsabout the Ni(2) sire of
parkerite. The structuresdifter, principally, in the
N i ( 2 ' )- -
Ni(t')
c
i(l")
Frc. 1. The crystal structure of parkerite. Ni(l): small
full circles;Ni(2): small half-closedcircles;Bi: large open
circles;S: stippledcircles.
Ftc. 2. The crystal structure of shandite, arranged to
ernphasize the relation of the parkerite structure to it; two
unit cell volumes of parkerite are outlined. Ni: small full
circles; Pb: large open circles-enclosednumbers differentiate
between the Pb(l) and Pb(2) sites; S: stippled circles.
439
CRYSTAL STRUCTURE OF PARKERITE
and 2.05A; a.e significantlyshorter than the average
value (about 2.3 A) for nickel sulfides,although Ni-S
distancesof 2.15A and 2.19A have been reported
for d-Nizs6 and millerite respectively(Fleet, 1972).
The Ni-S-Ni bond anglesapproach90o, suggesting
that the o bondsto the Ni are formed with p orbitals.
The short Ni-S bond distancessuggestsome degree
of multiple bond formation, the o bonds being
augmentedby z'bonding betweenthe 3sorbital on the
S and the d"o,d,", and dn" orbitalson the Ni atoms.
The bond distancein metallicNi is 2.492A, and it
has been suggestedthat similar Ni-Ni distancesin
and millerite representbond
a-NirS6,heazlewoodite
numbers of unity (Fleet, 1972).The nearest Ni-Ni
distancesin parkerite(2.72 L and.2.77 A) are too
long for full bonds but clearly representsomedegree
of orbital interaction. The geometry of the Ni sites
requiresthat this interaction must take place in the
form of o bonding between the d"n, d"., and do"
orbitals. Now, both Ni-S r bonding and Ni-Ni
o bonding possibilitieswould be prohibited if these
3d orbitals were filled; indeedthe close approach of
the Ni atomsis itself good evidencethat theseorbitals
are not filled. The dispositionof the four Ni(l) atoms
coordinated to each Bi would require participation
of the 6s electronson the Bi atoms in the Ni-Bi o
bonds. The Bi and S atoms, then, contribute 18
electronsto the 12 Ni-Bi and 6 Ni-S o bonds so that
each Ni must contribute 6 electrons, two 4s and
four 3d. The four 3d electronson the Ni atoms can
be contributed to these bonds only via the d",-,'
and d", orbitals; it is assumedthat the actual bonding
orbitals to the Bi and S atoms are octahedrald'sp"
hybrid orbitals. This argument requires that only
four 3d electrons remain to populate the d,o, d,",
and do" orbitals, allowing theseto participate in the
Ni-S z' bonding and Ni-Ni o bonding interactions.
The Ni atoms in parkerite are distributed so that
the structureis reducedessentiallyto (010) layers
0, 1 etc. (Fig. l).
of Ni-(Bi, S) octahedraaty:
Of the 18 Ni-Bi and Ni-S o bondsper unit cell, only
one (a stretchedNi(2)-Bi bond) bridgestheselayers and this readily explainsthe excellent {010}
cleavageof parkerite.
The extensivesolid solution of Pb in parkerite and
the very limited solid solution of Bi in shanditemust,
in part, relate to the disorderedstructureof parkerite; intuitively, a disorderedstructure would accommodate a foreign atom more readily than an
ordered one. Beyond this statement,further crystal
chemical comparisons between the two structures
are hinderedby the uncertaintyin the S positionsin
shandite. In this regard, though, crystal chemical
analysis of the structure does favor the positions
suggested
by Peacockand McAndrew.The P, orbital
on the Pb(2) atom would not participatein the o
bonding to the Ni atoms, since all of the Ni atoms
coordinatedto Pb(2) form a hexagonalring in the
plane normal to this orbital, and would be available
to form a o bond with the 3s orbital on the S. This,
in turn, would exclude z, bonding betweenS and Ni
(unlessit involved the empty d orbitals on the S)
resulting in conventional Ni-S bond lengths in
shandite.
Acknowledgments
This work was supportedby a National ResearchCouncil
of Canada operating grant.
References
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computed from self-consistent field relativistic DiracSlater wave functions. Acta Crystallogr. lt, 77-23.
exo J. B. MINN (1958) X-ray scattering factors
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oB Mr,urBxeen, J. eNo H. Torvrpe (1965) The absorption
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Manuscript receiued,luly 3, 1972; accepted
for publication, December 22, 1972.