Miner Petrol (2011) 101:75–80
DOI 10.1007/s00710-010-0137-3

ORIGINAL PAPER

Plumboselite, Pb3O2(SeO3), a new oxidation-zone mineralfrom Tsumeb, Namibia
Anthony R. Kampf & Stuart J. Mills & William W. Pinch

Received: 11 September 2010 / Accepted: 1 October 2010 / Published online: 20 October 2010
# Springer-Verlag 2010

Abstract Plumboselite, ideally Pb3O2(SeO3), is a newselenite (IMA2010–028) from the Tsumeb mine, Namibia.
It occurs as fibres on clausthalite and is also associated withsmithsonite, mimetite and vaterite. Plumboselite occurs insubparallel to divergent clusters of thin, flattened, colourless fibres up to 0.3 mm in length, but not exceeding 5 μmin width and 2 μm in thickness. The fibres are elongatedparallel to [001] and flattened on {010}, with {010} the
only form observed. The crystals have a dull to adamantine
lustre and a white streak. The tenacity is brittle and theMohs hardness is estimated to be between 2 and 3.
Plumboselite crystals are optically biaxial with parallel
extinction and are length fast in all orientations. The
Gladstone-Dale relationship predicts nav =2.115. The highindices of refraction and small crystal size prevented thedetermination of other optical properties. The calculateddensity is 7.814 g/cm3. The empirical formula (based on 5O atoms) is Pb2.92Ca0.01Se1.03O5. Plumboselite is orthorhombic, space group Cmc21, a=10.5384(11), b=10.7452

Editorial handling: R. Abart
A. R. Kampf (*)
Mineral Sciences Department, Natural History Museum of Los
Angeles County,
900 Exposition Boulevard,
Los Angeles, CA 90007, USAe-mail: akampf@nhm.org
S. J. Mills
Department of Earth and Ocean Sciences, University of British
Columbia,Vancouver, British Columbia, CanadaV6T 1Z4
e-mail: smills@eos.ubc.ca
W. W. Pinch
19 Stonebridge Lane,Pittsford, NY 14534, USA(13), c=5.7577(7) Å, V=651.98(12) Å3 and Z=4. The fivestrongest lines in the powder X-ray diffraction pattern are[dobs in Å/(I)/hkl]: 3.155/(100)/221; 1.956/(26)/042,402;
2.886/(22)/311,002; 1.713/(21)/223; 2.691/(17)/040. The
crystal structure was solved from single-crystal X-ray
diffraction data and refined to R1 =0.0371 on the basis of
200 unique reflections with Fo >4σF. The structure isbased on double [O2Pb3] chains of edge-sharing oxocentered [OPb4] tetrahedra along c, between which aresited SeO3 triangles. The two independent Pb2+ atoms andthe Se4+ atom have sterochemically active lone electronpairs.

Introduction
As noted by one of the authors (WWP) in his introduction
to the Tsumeb issue of the Mineralogical Record (Wilson1977), “Tsumeb is most likely the greatest of the great(mineral localities).” This assessment was based upon its
prolific production of “classic” mineral specimens of remarkable size and beauty, as well as an incredible diversity of rare
and unusual species. Currently, the Tsumeb mine in theOtjikoto Region of Namibia (19°15′ S, 17°42′ E) is recognised
as the type locality for 60 new minerals and 266 mineral
species in total (G. Gebhard pers. comm.).
In the 1970s and 1980s, Dr. John Innes served as
mineralogist for the Tsumeb Corporation and was instrumental in the discovery of many unusual specimens. Amongthem, were three specimens of clausthalite, which represent
the first reported occurrence of a selenium-bearing mineral at
Tsumeb. Gebhard (1999) noted that “The clausthalite
crystals are covered by the only known selenate from
Tsumeb GS 19, still under investigation.” Unknown “GS19”, to which Gebhard referred, is actually a selenite, rather
than a selenate. It is described herein as a new mineral.

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The name is in reference to the mineral’s chemicalcomposition, plumbo (for lead) and sel (for selenite). The
mineral and name have been approved by the IMA
Commission on New Minerals, Nomenclature and Classification (IMA2010–028). The holotype specimen is preserved in the collections of the Mineral Sciences
Department, Natural History Museum of Los Angeles
County, catalogue number 63264.

Occurrence and paragenesis
Plumboselite is known to occur on only three specimens.
All three specimens were collected by the late John
Innes, probably from the same isolated occurrence.
While no information appears to have survived regarding
the specific location of this occurrence in the mine, we
assume it to be in the second oxidation zone, on or in
the vicinity of the 30 level, because this was the part ofthe mine being actively exploited in the late 1970s,around the time the clausthalite specimens were found.
The holotype specimen was previously in the collection

A.R. Kampf et al.
Table 1 Electron microprobe analytical data for plumboselite
Constituent

Wt.%

Range

Stand.
Dev.

Probe
Standard

CaO

0.09

0–0.34

0.12

Diopside

PbO

84.92

83.49–86.66

1.09

Galena

SeO2

14.95

13.18–17.20

1.40

Se metal

Total

99.96

97.00–101.10

1.36

Table 2 X-ray powder diffraction data for plumboseliteIobs

dobs(Å)dcalc(Å)

Icalc

hkl

77.58227.52124110

55.3271

5.37212020

5.266022002

4.56444.57101111

23.9411

3.92742021

100

3.15493.1482

100

221

22

2.88582.88702311

2.878123002

172.69122.686117040

11

2.63952.633018400

12.52532.52552202

32.30142.29854331

122.19652.209532412.19422132

2.18703421

2.17943

312

1.963722042

1.9427

23

402

26

1.956113

1.88641.8803

20

440

21

1.71291.7091

29

223

11

1.62891.626326261

121.60511.602629621

111.57671.574122442

2

1.5241

1.52372333

1.52042062

21.49711.50421550

1.49861602

1.49691243

1.489824230043

1.44291.439052

1.3463

1.34851731

1.3430

3080

3

17

1.31891.27111.31881533

1.31672462

1.31655800

1.270512263

1.26933281

1.26856044

Iobs and dobs from profile fitting using JADE 9.1
Fig. 1 SEM image of plumboselite

Icalc and dcalc calculated from crystal structure using JADE 9.1

Plumboselite, Pb3O2(SeO3), a new mineral from Tsumeb
Table 3 Data collection andstructure refinement details forplumboselite

Rint =Σ|Fo2 −Fo2 (mean)|/Σ[Fo2 ].

GoF=S={Σ[w(Fo2 −Fc2 )2 ]/(n−p)}1/2 . R1 =Σ||Fo|−|Fc||/Σ|Fo|.
wR2 ={Σ[w(Fo2 −Fc2 )2 ]/Σ[w(Fo2 )2 ]}1/2 . w=1/[σ2 (Fo2 )+(aP)2 +bP] where a is 0, b is 0 and
P is [2Fc2 +Max(Fo2 ,0)]/377

Diffractometer

Rigaku R-Axis Rapid II

X-ray radiation/power
Temperature
Structural FormulaSpace group
Unit cell dimensions

Z
VolumeDensity (for above formula)
Absorption coefficientF(000)
Crystal sizeθ range
Index ranges

MoKα (λ=0.71075Å)/50 kV, 40 mA298(2) KPb3O2(SeO3)
Cmc21
a=10.5384(11) Åb=10.7452(13) Åc=5.7577(7) Å4651.98(13) Å3
7.952 g/cm3
82.807 mm−1
1280
38×5×2 μm
3.79 to 18.84°−9≤h≤9, −9≤k≤9, −4≤l≤5Reflections collected/unique
Reflections with Fo >4σF
Completeness to θ=27.48°
Max. and min. transmission
Refinement method
Parameters refined
GoF
Final R indices [Fo >4σF]
R indices (all data)Extinction coefficient
Largest diff. peak/hole
Flack parameter

1110/258 [Rint =0.0802]
20098.7%0.8519 and 0.1450
Full-matrix least-squares on F2350.897
R1 =0.0371, wR2 =0.0650
R1 =0.0500, wR2 =0.0715
0.00016(6)+1.025/−1.110 e/A30.06(8)of one of the authors (WWP) and another specimen
remains in his collection. The third specimen is currently
in the collection of Dr. Mark Feinglos.
Plumboselite occurs on clausthalite and clearly formed
as an oxidative alteration thereof. Other associated minerals
on the specimens include smithsonite, mimetite andvaterite.

Physical and optical properties
Plumboselite occurs in subparallel to divergent clustersof thin, flattened, colourless fibres up to 0.3 mm inlength, but not exceeding 5 μm in width and 2 μm inthickness (Fig. 1). The fibres are elongated parallel to[001] and flattened on {010}, with {010} the only form

Table 4 Atomic coordinates and displacement parameters (Å2) for plumboselite
xyz

Ueq

U11

U22

U33

U23U13U12

Pb1

0.00.8816(2)0.814(2)0.0204(14)0.0197(19)0.0162(17)0.025(2)−0.007(5)0.0

0.0Pb20.24794(19)0.11233(14)0.8125(8)0.0199(11)0.0200(14)0.0207(14)0.0190(16)0.002(5)0.006(3)−0.0053(10)

Se

0.5

0.8698(6)0.8652(15)0.024(5)0.000(5)0.032(5)0.041(15)0.001(5)

0.0

0.0O1

0.138(2)1.000(7)0.048(13)0.029(8)O2

0.5

0.723(3)0.765(9)0.015(12)O30.624(3)0.930(3)0.717(5)0.028(10)78

A.R. Kampf et al.

Table 5 Selected bond distances (Å) in plumboselite
Se–O2
Se–O3(×2)<Se–O>

1.68(4)
1.69(3)
1.687

Pb1–O1(×2)
Pb1–O1(×2)

2.35(6)
2.46(6)

Pb1–O2
Pb1–O2<Pb1–O>

2.83(5)3.36(5)
2.635

Pb2–O1Pb2–O1Pb2–O3Pb2–O3Pb2–O2Pb2–O32.16(6)2.26(6)2.44(3)2.73(3)2.886(13)3.70(3)Pb2–O3<Pb2–O>

3.71(3)2.848

needles with a Cameca SX50 electron microprobe at theDepartment of Earth and Ocean Sciences, University ofBritish Columbia. Operating conditions were 20 kV, withbeam current of 5 nA and a 1 μm beam diameter. Raw
intensity data was corrected using a PAP matrix
correction (Pouchou and Pichoir 1984). No other elements
were detected by energy dispersive spectroscopy. The
results, as well as the standards used, are provided inTable 1.

observed. Plumboselite fibres are transparent, have a dull
to adamantine lustre and a white streak. The hardness isestimated to be between 2 and 3. The tenacity is brittle,
no cleavage or parting was observed and the fracture
could not be ascertained due to the size of the fibres. Thedensity could not be measured because it is greater thanthose of available high-density liquids and there isinsufficient material for physical measurement. The calculated density is 7.814 g/cm3 based upon the empirical formulaand single-crystal unit cell.
Optically, plumboselite is biaxial, however the sign, 2Vand dispersion could not be determined due to the size ofthe crystals and the indices of refraction are higher thanavailable index fluids. The Gladstone-Dale relationship(Mandarino 1981) predicts nav =2.115. The optical orientation could only be partially determined: X=c. The extinction is parallel and fibres are length fast in all orientations.

Chemical composition
Quantitative wavelength-dispersive electron-microprobe
analyses (7 points) were carried out on plumboselite

Table 6 Bond valence sums for plumboselite

O1O2

Pb1

Pb2

0.454 x2↓
0.363 x2↓
0.170
0.058

0.669
0.545
0.152

O3

Sum

1.862

0.378
0.189
0.029
0.028
1.990

SeSum
2.031

1.425

1.895

1.387 x2↓

2.011

4.199

Pb2+ –O bond strengths from Krivovichev and Brown (2001) and Se4+ –O
bond strengths from Brese and O’Keeffe (1991)

Fig. 2 Crystal structure of plumboselitePlumboselite, Pb3O2(SeO3), a new mineral from Tsumeb

79

Fig. 3 Se, Pb1 and Pb2 coordinations in plumboselite. In
each case, the stereoactive loneelectron pairs are oriented
approximately upwards

The empirical formula (based on O=5) is Pb2.92Ca0.01
Se1.03O5. The simplified formula is Pb3O2(SeO3), which
requires PbO 85.78 and SeO2 14.22, total 100 wt%.

X-ray powder diffraction data
X-ray powder-diffraction data (Table 2) were collected on aRigaku R-AXIS Rapid II curved imaging plate microdiffractometer using monochromatized MoKα radiation at
the Natural History Museum of Los Angeles County. Unitcell parameters, derived from whole pattern fitting using
JADE 9.1 software are: a=10.5505(8), b=10.7601(9) and c=
5.7671(5) Å and V=654.71(9) Å3, which are in good
agreement with those obtained from the single-crystal study(see below).

Single crystal X-ray diffraction
The structure data collection was performed using thesame instrument noted above. The Rigaku CrystalClearsoftware package was used for processing of thestructure data, including the application of an empiricalabsorption correction. Application of a shape-based
absorption correction was found to be unsuitable becauseof the very small and thin nature of the fibre. Note that
because of the small crystal size the dataset was limited
to a resolution of 1.1Å (θ=18.84°). This thwarted ourefforts to refine anisotropic displacement parameters for
the O atoms. The structure was solved by direct methods
using SIR92 (Altomare et al. 1994) and the location of allatoms was straightforward. SHELXL-97 (Sheldrick 2008)
was used for the refinement of the structure. The details of
the data collection and the final structure refinement areprovided in Table 3. The final atomic coordinates anddisplacement parameters are in Table 4. Selected interatomic distances are listed in Table 5 and bond valences inTable 6.

Description of the structure
The crystal structure of plumboselite is identical to that ofsynthetic Pb3O2(SeO3) as described by Krivovichev et al.
(2004) and Kim et al. (2009). The structure contains two Pbatoms, one Se atom and three O atoms in the asymmetricunit. The structure is based on double [O2Pb3] chains ofedge-sharing oxo-centered [OPb4] tetrahedra along c,
between which are sited SeO3 triangles (Fig. 2). The lonepairs for both Pb2+ atoms and the Se4+ atom are stereoactive, as evidenced by the lopsided geometries of the Pb2+
and Se4+ coordinations (Fig. 3). Kim et al. (2009) pointed
out the importance of the stereoactivity of the Se4+ indetermining the non-centrosymmetric symmetry of thephase and, consequently, its piezoelectric and pyroelectricproperties.
The average Pb1-O and Pb2-O bond lengths are 2.635
and 2.848Å, respectively, and the average Se–O bondlength is 1.687Å. All values are consistent with typicaloxysalt minerals, as well as those lengths reported by both
Krivovichev et al. (2004) and by Kim et al. (2009). Notethat we have included Pb–O bonds up to a bond-length of3.71Å; however, an O2 at a distance of 3.68Å from Pb1 is
not included because it is on the same side of the Pb as are
the four short Pb–O bonds and, therefore, it is unlikely tocontribute to the Pb1 coordination.
Numerous minerals and synthetic phases have oxocentered [OPb4] tetrahedra (Siidra et al. 2008). Of thesecompounds, only twelve have [O2Pb3] chains, and only
three are minerals: chloroxiphite (Finney et al. 1977),
mendipite and damaraite (Krivovichev and Burns 2001).
Among all of these phases, the plumboselite structure-type
is unique.

Acknowledgements The Associate Editor, xxxx and two anonymous
reviewers, provided helpful comments on the manuscript. This study wasfunded in part by the John Jago Trelawney Endowment to the MineralSciences Department of the Natural History Museum of Los AngelesCounty.

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