Arsendescloizite
a new mineral from Tsumeb
by Paul KeUer
Institut fur Mineralogie und Kristallchemie
Universitat Stuttgart
Pfaffenwaldring 55
D-7000 Stuttgart, West Germany

ABSTRACf
Arsendescloizite, PbZn(OH)(As04), was found as yellow tabular
crystals intergrown in rose-like aggregates in tennantite ore fromTsumeb, Namibia, associated with willemite, chalcocite, mimetite,quartz and goethite.
Microprobe analysis gave PbO 52.3, ZnO 18.5, FeO 0.3, As20s
26.5, H20(TGA) 2.9, sum 100.5 percent. Cell contents for As = 1
are: PbI.06(Znl.o3Feo.o2)I:l.osHI.46AsIOs.34 ideally PbZn(OH)(As04) for which Deale. = 6.57 g/cmt. Slightly soluble in hot
HN03.
X-ray single crystal study showed it to be orthorhombic,
P212\21, a 6.075(2), b 9.358(2), C 7.634(2) A, Z = 4. The strongest
lines in the X-ray powder diffraction pattern are: 3.23(10)(102),
2.88(10)(031,210), 2.60(8)(131), 1.559(8)(313,251,060), 4.23(6)(Ill), 2.09(6)(231), 1.656(6)(331,143,233)A.
,Crystals are tabular on {001}. Observed forms are {001}, {OIl}, _{1Ol} and {Ill}. Color pale yellow, transparent. Luster sub-.
adamantine, brilliant. Streak white. Hardness (Mohs) about 4.
Biaxial negative, 2V about 30(5)°, dispersion r > v, with a 1.990(5),(32.030(5), 'Y 2.035(5). Optical orientation: X = b. Y = a, and Z =c.
The name is for the chemical and crystallographic relations todescloizite, which is the vanadium analog of this mineral.
OCCURRENCE
Arsendescloizite was brought to our attention by Wolfgang
Bartelke, who submitted for identification a pale yellow minerallooking like adamite or tsumcorite. Surprisingly, the powder diffraction pattern was nearly identical with that of descloizite.
However, there was no trace of vanadium, so we became convincedthat we were dealing with a new species, probably the arsenic
analog of descloizite.
Arsendescloizite was found as a secondary mineral on a matrix ofcopper ore consisting mainly of tennantite, (Cu,Fe)\2As4S13, andchalcocite, Cu2S. The new mineral is associated with willemite,
Zn2Si04, in water-clear prismatic crystals, with euhedral chalcocite
crystals, corroded mirnetite [PbsCI(As04hl, quartz, and goethite[oo-FeOOH], in order of abundance. The observed sequence ofdeposition, from the oldest to the youngest, is:chalcocite - quartz - mimetite - arsendescloizite goethite - willemite
Unfortunately, we have no information about which part of themine our specimens came from.
The Mineralogical Record, May-June,

1982

and Pete J. Dunn
Department of Mineral Sciences
Smithsonian Institution
Washington, DC 20560

PHYSICAL and OPTICAL PROPERTIES
Arsendescloizite crystals are tabular on {001}, up to 0.1 x 0.4 x
0.5 mm in size and intergrown as rose-like aggregates "(Fig. 1).
Observed forms are {00l}, {OIl}, {1Ol}, and {Ill} (Fig. 2). The
new mineral is pale yellow with a brilliant subadamantine luster.
The streak is white and the hardness (Mohs) is about 4. No cleavage
was observed.
Arsendescloizite is optically biaxial negative, 2V about 30(5)°,dispersion r > v. The indices of refraction are a 1.990(5), (32.030(5),and 'Y 2.035(5), with the optical orientation X = b, Y = a, and Z= c. Calculation of the Gladstone-Dale relationship using the constants of Mandarino (1976) and the calculated density yields a value

1. Arsendescloizite: tabular crystals
intergrown in rose-like aggregates. Size: 3 mmwide. Collection of W. Bartelke; photo by J.
Weber.

Figure155c=z(001)

b=Xao»
a=Y
Figure 2. Arsendescloizite: idealized drawing

with faces and optical orientation.

of KC = 0.152, in good agreement with the value calculated forphysical properties, Kp = 0.155.
X-RAY DIFFRACTION STUDY
A small fragment of a euhedral crystal was examined by Weissenberg and precession techniques and finally measured with an automatic four-circle diffractometer.
Arsendescloizite is orthorhombic; systematic absences show thespace group to be P212t21• The unit cell parameters are a =6.075(2), b = 9.358(2), and c = 7.634(2) A. For Z = 4 and theideal formula, the calculated density is Deale. = 6.57 g/cm-. A powder diffraction pattern (Table I) was obtained using a 114.6-mmdiameter Debye-Scherrer camera and FeKa X-radiation without

Table 1. Indexed powder pattern for arsendescloizite,PbZn(0H)(AsVs4), Fe-Ka radiation, camera diameter 114.6 mm.
Intensity 1/10 is estimated.
dobs.

(A)

5.09
4.67
4.23
3.98
3.54
3.33
3.23
3.04
2.88
2.70
2.66
2.60
2.55
2.46
2.42
2.30
2.24
2.10
2.09
1.970
1.911
1.877
1.850
1.788
1.764
1.720
1.678
1.668
1.656
1.618
1.559
156

1110

deale. (A)

hkl

4
56
1
2
2
10
3
10
4
58
122
4
5
16
1
2
52
5
3
4
1
164
• 8

5.088
4.680
4.238
3.990
3.535
3~336
3.231
3.037
2.889, 2.8872.703
2.659
2.608
2.549
2.456
2.417, 2.415
2.303
2.237, 2.236
2.099, 2.098
2.092
1.972
1.909
1.876
1.854
1.789, 1.789, 1.787
1.767
1.723
1.681
1.671, 1.6,67
1.658, 1.657, 1.654
1.620, 1.616
1.562, 1.560, 1.560

110020
111
021
012
121
102
200
210, 031
211
122
131
220
013
221, 032
212
041,023
141, 123
231
033
400
133
240
150, 302, 114
024
043
052
322,242
331,143,233
152,204
313, 060, 251

standards. The calculated d values and the indices are derived fromfour-circle diffractometer data. The intensities I I 10 were estimatedvisually.
CHEMICAL ANALYSIS
Arsendescloizite was chemically analyzed using an ARL-SEMQ
electron microprobe with an operating voltange of 15 kV and abeam current of 0.15 pA. The results were corrected for background, backscatter, fluorescence and absorption using theMAGIC-4 computer program. The standards used. were: synthetic
olivenite for As, synthetic ZnO for Zn, synthetic PbO for Pb, andanalyzed hornblende for Fe. The new mineral was checked for thepresence of elements with atomic number greater than 9 by electron
microprobe wavelength-dispersive scan but none were found except
those reported in Table 2.
Table 2. Electron microprobe analysis of arsendescloizite,

PbZn(0H)(As04),

H20 by TGA, in weight percent.

Analytical No. of atoms Theoretical No. of atoms
FeO
ZnO
PbO
As20s
H2O

0.3
18.5
52.3
26.5
2.9

Total

100.5

FeZn
PbAs
H
0

0.02
1.03
1.06
1.00
1.46
5.34

18.99
52.09
26.82
2.10

Zn
PbAsH
01.00
1.00
1.00
1.00
5.00

100.00The water content was determined with a thermo balance using a
6.8 mg sample of arsendescloizite. There is a 2.9 weight percent
water loss at a mean temperature of 530 C. The heating rate
was 100 C/minute.
Arsendescloizite is slightly soluble in hot HN03.
The empirical formula was calculated on the basis of As = 1
because the water determination may not be of high accuracy, inview of the very small sample weight. The result is:
Pbl.o6(Zn l.o3FeO.02)l:l.osH1.46As1Is.34
and idealized: PbZn(0H)(As04):
0DISCUSSION
According to chemical composition alone, the new mineral could
be the zinc analog of duftite, the lead analog of austinite, or thearsenic analog of descloizite. However, since the powder diffraction pattern of the new mineral is most similar to that of descloizite,
it is named arsendescloizite. Also, there have been reported arseniccontaining descloizites from several localities (Palache, Berman andFrondel, 1951)with a maximum content of As20s 7.13 weight percent (Bannister, 1933). Such arsenic-containing varieties ofdescloizite were named "araeoxene" by Von Kobell in 1850(Strunz,1970). Arsendescloizite is the pure end member of a possible solid
solution series with descloizite. Surprisingly, the analyzed arsendescloizite contains no vanadium, copper or calcium.
The Mineralogical Record, May-June,

1982

NAME and TYPE SPECIMENSThe name is for the chemical and crystallographic relationship todescloizite, which is the vanadium analog of this mineral.
The Commission on New Minerals and Mineral Names, I.M.A.,
has approved the new mineral and its name prior to publication.
Type material will be deposited in the Institut fur Mineralogie undKristallchemie, Universitat Stuttgart, D-7000 Stuttgart 80, Federal
Republic of Germany, and in The Smithsonian Institution, Washington, D.C. 20560.
ACKNOWLEDGMENTS
We thank Wolfgang Bartelke, Mainz, for the generous loan ofspecimens, H. Hess, Stuttgart, for the diffractometer measurement, J. Weber, Mamaroneck, for the photomicrograph.

REFERENCESBANNISTER, F. A. (1933) The identity of mottramite and psittacinite with cupriferous descloizite. Mineralogical Magazine, 23,376.
MANDARINO, J. A. (1976) The Gladstone-Dale relationship,
Part I: Derivation of new constants. Canadian Mineralogist,14,498.

PALACHE, c., BERMAN, H., and FRONDEL, C. (1951) The
System of Mineralogy, 7th Ed., Vol. II, 811. John Wiley andSons, New York.
STRUNZ, H. (1970) Mineralogische Tabellen, 323, Akademische
Verlagsgesellschaft, Leipzig.
w:w:re:ar r.s

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