Leltelte: a new rnlnerel jrorn Tsumeb

byFabien P. Cesbron", Richard C. Erd**,Gerald K. Czamanski**, and Helene Vachey*"Laboratoire de Mineralogie-Cristallographie
associe au CNRS,
Universite P. et M. Curie, 75230 Paris Cedex 05 France""U.S. Geological
California 94025

Survey, 345 Middlefield

Road, Menlo Park,

ABSTRACT
Leiteite ("Ia'-lll") is a new zinc arsenite found associated withtennanrite,
chalcocite,smithsonite,and schneiderhohnite
atTsumeb (Southwest Africa). It occurs as cleavable masses to~ em in greatest dimension, colorless to brown and transparent;
the Mohs hardness is 1]/2 - 2 and the observed density is 4.3( I).
The cleavage lamellae on {tOO} are flexible but inelastic andhave a pearly luster. Leireite is optically biaxial positive with
0=1.87(1),,6=1.880(5),r=1.98(l),and2V=26Y2(])O;\Aa = 11 0, Y = b. ZAc = +10°; r < II, very strong. X-ray
Jiffraction shows space group P2/ a with a = 17.645(5)A. b =:;.019(2), c = 4.547(2), and ,6 = 90° 59(4)'. The most intense
powder diffraction lines (in A) are 3.133 (l00) (211 L 3.163(6):: II), 1.685 (49) (911),3.320 (39) (Ill), 3.302 (32) (111),4.833 (31 )110), but strong preferred orientation due to perfect cleavage
can change this order. Wet chemical analysis yields the formula
I Zno.9sFeo-o2)As204 with four
formula units in the cell. The
name is for Luis Teixeira-Leite,mineralogist,of Pretoria.
Republic of South Africa.
INTRODUCTION
The new mineral leiteite was discovered some years ago byLuis Teixeira-Leite among specimens from Tsurneb (SouthwestAfrica); unfortunately
it is impossible to determine from theminers the exact location in this deposit from which the specimens were obtained.
The leiteite was found as a single
specimenv?
x 4 x 0.3 em, which was subsequently divided into
several pieces for mineralogical studies and museum specimens
lone of these is shown as figure 1). Parts of the original specimen have been depositedin the SmithsonianInstitution
I National
Museum of Natural History), Washington,D.C., inrhe British Museum (Natural History), London, and in thevlineralogicalCollection of the P and M. Curie University,Paris. Leiteite (pronounced" la' tIL") is named in honor of its
discoverer.

The name and species have been approved by the Commission on New Minerals and Mineral Names, I.M.A.
OCCURRENCE
Leiteire occurs as colorless to brown cleavable masses; oneof the larger fragments of the single known specimen is shownas Figure I. Although the study of leiteite did not begin until
after it had been brought from the mine and broken into several
pieces, we can make some fairly good guesses as to its locationin the mine and its paragenesis based on the minerals associatedwith it. Almost all of the fragments we examined were leiteite
only, but on one piece we found platelets of leireite with smithsoniie on a matrix of tennantite.
Most fortunately,
at a later
date, Peter Embrey sent us a description of the leiteite specimen in the MineralogicalCollection of the British Museum(Natural history) "Specimen
B.M. 1976,235. Several bruisedand cleaved crystals 4 to 10 mm across, near 6 mm and smallercleaved black grains of schneiderhohnite
on a matrix of mixedsulfides. mainly chalcocite.
No morphology
is observable."
Schneiderhohnite,8(Feo.96ZnO'03GeO'Ol)O·5As203, is a rare arsenite known so far only from a single occurrence in the Tsumeb
mine (Ottoman et al., 1973). It was discovered
here a few
metres below the 29 level (908 m) in a small druse in thedolomite-chert
breccia near its contact with pseudo-apliteinthe "deep oxidation zone." The schneiderhohnitc
was associated with chalcocite and z incian stortite with traces of relict
pyrite, termantite, and galena as accessory minerals. According
to Ouernan et al. (1973) schneiderhohnite
is a secondary
mineral which probably formed at a temperatureof 40°C.
Thus. while the schneiderhohnite
found on the leireite specimen in the British Museum may be a second occurrence of themineral at Tsurneb, it seems likely that it came from the vicinity of the original discovery and that leiteire formed under thesame conditions. It is worth noting that the zinc orthoarsenire,reinerite, 3ZnO' As203, was found in cavities about 10 metres
below the 29 level associatedwith bornite and chalcocite(Geier and Weber, (958).
PHYSICALAND OPTICALPROPERTIESl.eiteiie exhibits no crystal forms, but a perfect (lOO} cleavage
was observed. The cleavage lamellae are flexible, inelastic.
and somewhat secrile. The mineral has hardness between I\!2and 2 (Mohs). Density, measured with a pycnometeron an
uncrushed 500 mg sample, was 4.3(1); the value is slightly low
due to air entrapped between cleavage surfaces.
Leiteire is colorless to pale brown and transparent,with apearly luster on the cleavage. Optically it is biaxial positive.
Accurate determinationof indices of refraction with high immersion media is difficult as the mineral is slowly attacked bythese liquids. Leiteite is non fluorescent. Optical data and orientation are given in table 1 and figure 2.
X-RA Y DIFFRACTION
STUDY
A small cleavage fragment. carefully squeezed between two
glass slides to flatten it. was examined by precession techniques
using MoK 0 (,\ = 0.7107 A) radiation. Leiteite is monoclinic,
pseudo-orthorhombic.
and systematic absences show the spacegroup to beP21Ia.
Unit cell parameters,
after least-squares refinementof thepowder diffraction data, are a = 17.645(5) X, b = 5.019(2),c = 4547(2), and ,6 = 90° 59(4)/. The calculated density with
4[(Zno'98Feo.o2)As204l is 4.61 g/cc.
A powder diffraction pattern was obtained using a Nonius
Guinier camera and quartz as the internal standard. Relative
intensities were obtained by measuring the film with a Joyce
microdensitometer.
X-ray powder data for leiteite are given intable 2. Because of its perfect {l00} cleavage. diffractometer
traces of leiteite show strong preferred orientation; the diffractometer intensities (IDi are comparedin table 2 with thosemeasured fr0111the Guinier film ([G1.
CHEMICALCOMPOSITION

Leiteite was analyzed by two different methods. (1) Samples
were analyzed with an ARL EMX-SM electron microprobe
using an accelerating voltage of 15 KV and a specimen current

95

I. Table 1.
Optical propertiesof lelteite.

I.1

I= 1.87(1)ar= 1.880(5)= 1.98(1)(+)2V= 261/2(1)0

XAa=+110

ZAc= +100

Y=bf3

Il ._~~___~~~

JFigure 1. Leiteite fragmentin (above) transmitted and (below)
reflected light. The fragment is 22 mm long.
Figure 2. (right) Edge view of plate showing optical orientationfor leiteite.

r«: v, very strong
optic axial plane {OlG}
Indices determined
inboth sodium light andwhite light.

Table 2. Indexed powder pattern for leiteite (CuKcx:radiation, A = 1.5405981 A).

of 2 x 10-8 amperes on benitoite. The Ka lines of both As andZn were analyzed using LiF crystals. (The La line of As, though
exhibiting a better peak-to-backgroundratio as analyzed by an
ADP crystal, encounters heavy absorption by Zn that is apparently overestimatedby Heinrich(1966), and consequentlyovercompensatedby FRAME, the theoretical
data reduction
program utilized.I Recrystallized reagent grade Asz03 and ZnO
were used as standards. Because Asz03 is noticeably affectedby even a defocussed beam, counts were taken on it with abeam 10 microns in diameter, whereas the fine-grained ZnO
standard and micaceous
plates of leiteite required a wellfocussed beam. Two independent
analyses of the new mineral
were made, each relying on 10 counts of 10 seconds each forboth the standards and the mineral. Count termination
wasmade in the fixed beam current mode to compensate
forpossible fluctuation in beam energy. Count data were correctedby the computer reduction scheme, FRAME, of the U.S. National Bureau of Standards (Yakowitz et al., 1973). Assigned
error limits represent
one standard deviation as determinedfrom counting data on the new mineral. (2l Samples were also
analyzed by wet chemical analysis. Arsenic, after oxidation
with HN03, was determinedby the molybdenum
blue colorimetric method. Both zinc and iron were determined by atomic
absorption spectrophotometry.
Leiteite dissolves slowly in cold

96

hkl

d calc.(A)

200
110
400
011
Til
111
211
211
600
311
311
510
411
411
020
511
220
002
202
202
420
112
321
402
402
811
811
10·0·0911022
130
10·1·0
131
231

8.818
4.828
4.409
3.369
3.318
3.302
3.162
3.135
2.941
2.940
2.908
2.887
2.695
2.661
2.510
2.452
2.414
2.273
2.210
2.192
2.181
2.053
2.053
2.035
2.007
1.856
1.835
1.764
1.685
1.685
1.666
1.666
1.565
1.547

I(G). Intensity
I(D). Intensity

measuredmeasuredd cbs.' A)

I (G)

1(0)

s.scs
4.833
4.405
3.369
3.320
3.302
3.163
3.133
2.940

3144
39
32
76
100
26

2.908
2.884
2.694
2.660
2.510
2.452
2.414

10

2.273
2.211
2.193
2.180
2.053

I

32
6100

618
21
400

19

28
3

1
12

19

3
19
18
9
17
26
7

3

14
10
222
2
7

1

3
5

2.034
2.006
1.856
1.835
1.761
1.685

49

1.665

7

1.565
1.547

618broad

822

from Guinier film.
from diffractometer

3trace.

20,..

576

I~i\.'0016- --- -- - - -,--------.-"".:10:OIA.JT55~",,'1-".........
.:'~o:' "'.

- ...... ...---- ---.

"'SOD

300

'00

I/lAr,1007. <,V~~'oJ'OJ'->0...",

I

-M

500

'00

100

T-C

analyses

AnalysisAnalysis 2300of leiteite.

Microprobe

Zn
As

23.6 ± 0.4 %53.7 ± 1.1

23.6 ± 0.3 %53.4 ± 1.7

0--Calculated
Composition
for ZnAs204
23.41 %
53.84
22.75

IVet Methods
AnalysisZnO

28.5 %

Molecular

Ratios0.35030.971 }

Calculated
Composition
for ZnAs204
29.140.99

FeO'As2Oa

0.5
71.4

Total

100.4

0.007
0.36090.019
170.86100.00.: I HC1. Analytical
data are presented
in table 3. The wet.frernical analysis yields the formula(Zn,Fe)O· AS203 orZn,Fe)As204, with Zn:Fe = 98:2.
Leiteite is a zinc metaarsenite;
the compound was first syn''lesized by Avery (1906) and has some industrial importance~, a wood preservative.
Chemicallyit can be related
to'~ippkeite, CUAS204, but trippkeite
is tetragonal(Zernann,: 451). As noted above, zinc orthoarsenite,
Zna(As03lz,reincr iie, is also found at Tsumeb and apparently
formed under-irnilar conditions.
THERMAL BEHA VIOR

The thermal behavior of leiteite is shown in figure 3 by the''Jermogravimetric(TGA),
differential
thermogravimetric
TG J, and differential
thermo-analysis(DT AJ curves pre-ented. At first there is a major loss of As20a, followed by thexidation of a part of the remaining As20a to AS205; the A;"1sition on the TGA curve corresponds
to the temperature~07 a C) where the increased
weight induced by oxidation
equilibrates
the loss of weight due to sublimationof AS203.
When oxidation is complete (position B, 839°C), the compo-ition Zna(As04Jz is obtained, following the reaction
3 ZnAs204
O2 ....,. Zna(AS04)2
2 As20,.t+is~6TOC

700

Table 3. Chemical

1!

+A chemical analysis of the resulting product gave (wt. %):-'\S205 47.9, Fe203 0.84, and ZnO 49.9; this, disregarding theFc20a, yields the formula 2.94ZnO:As205 or Zna(As04Jz.

500

700

Figure 3. (far left) Thermogravimetric(TGA I, differential
thermogravimetric(DTG), and differentialthermo-analysis(DT A) curves for leiteite.
Figure 4. (left) DT A curves for leiteite innormal atmosphere ("A") and in nitrogen("B").

Between 9000 and IOOO°C. incongruent melting occurs withadditional loss of AszOa due to partial reduction:a chemical
analysis of the sample at position C (l 007 a C) gave (wt. %):AS205 42.8, Fe203 1.18, and ZnO 56.2.
The endothermic
peak (507°C) on the DTA curve corresponding to the loss of AS203, is very small and suggests thatoxidation(exothermic)
begins earlier than expected:
whenoxidation becomes preponderant,
it gives a large exothermicpeak (555°C). There is a small endothermic peak at 839°C anda more important one at 1007°C, corresponding
to the melting
point.
The DT A curves of figure 4 represent behavior in normal
and inert atmosphere. Curve "A" shows the thermal behaviorof leiteite in normal atmosphere:
the large exothermic peak at576°C corresponds to the oxidation of As20a. Curve "B" shows
the behavior of leiteite in an inert atmosphere(nitrogen): thetwo definite endothermic peaks at 5000 and 546°C corresponding to the loss of As20a: oxidation does not occur.
ACKNOWLEDGMENTS
We are grateful to Miss M. C. Sichere for her help in making
the thermal analyses. The manuscript has benefitted from thehelpful criticism of Howard T. Evans, Jr., and Mary E. Mrose,
U.S. Geological Survey. Some of the specimens studied weresupplied by A. L. McGuinness and P. Bariand. We thank Peter
Embrey for the information
concerning
the British Museum
specimen.
REFERENCES
AVERY, S. (1906) The constitutionof Paris green
homologuesJ.
Amer. Chem. Soc., 28, 1155-1164.

anditsGEIER, B. H. and WEBER, K. (1958) Reinerit, Zn3(As03)2,
ein neues Mineral der Tsumeb Mine Sudwestafrika.
NeuesJahrb. Mineralogie, Monatsh., 1958, 160-167.
HEINRICH,K. F. J. (966) X-ray absorption uncertainty
inthe electron microprobe.
New York, John Wiley and Sons:
296-377.
OTTEMANN, J., NUBER, G., and GEIER, B. H. (1973) Schneiderhohnit,
ein naturliches Eisen-Arsen-Oxid
aus der tiefen
Oxidationszone
von Tsumeb. Neues Jahrb. Mineralogie,Monatsh., 1973, 517-523.
YAKOWITZ,H., MYKLEBUST,
R. L., and HEINRICH.
K.
F. J. (1973) FRAME: an on-line correction procedure forquantitativeelectron probe analysis.
Dept. Commerce,Natl. Bur. Standards, NBS Tech. Note 796, 46 pp.

u.s.

ZEMANN, J. (1951) Formel und Kristallstruktur
Tscherm. Mineralog. Petro Mitt., 2,417-423.

des Trippkeits.

97