Jentschite (T1PbAs2SbS6)
a new sulphosalt
mineral from Lengenbach, Binntal (Switzerland)
STEFAN GRAESER

Natural History Museum CH-4001 Basel and Mineralogical Institute, University of Basel,
CH-4056 Basel, Switzerland
AND

ANDREAS EDENHARTER
Institut ftir Mineralogie und Kristallographie, Universit~it G6ttingen, D-37077 G6ttingen, Germany
Abstract
Jentschite, T1PbAs2SbS6, is a new sulphosalt mineral from the famous Lengenbach locality (Binntal,
Switzerland). It was discovered in association with numerous other T1-As-sulphosalts such as hutchinsonite,wallisite-hatchite, edenharterite, bernardite, abundant realgar and orpiment in small cavities in a dolomiticrock of Triassic age which forms part of the Penninic Monte-Leone-nappe. The first specimens consisted ofextremely small polysynthetically twinned crystals; a later find yielded less complicated twinned crystals insizes up to 2 mm length. Single crystal X-ray diffraction studies gave a monoclinic cell with a = 8.121(3), b =23.969(9), c = 5.847(3) A, B = 107.68(3) ~ V = 1084.3(5) ~3, Z = 4, space group P21/n. The strongest lines in
the X-ray powder diagram are (dobs in A, lobs, hkl): 2.823 (100)(116), 3.587 (86)(221), 2.778 (84)(260), 3.998(74)(060), 2.670 (58)(301), 3.816 (54)(210). Chemical composition (electron microprobe, mean of 15
analyses, wt.%) is: T1 23.92, Pb 21.44, As 19.16, Sb 12.53, S 22.42, total 99.47 wt.% from which a simplified
formula T1PbAsaSb~S6 can be derived. This formula is very close to that of the (orthorhombic) mineraledenharterite T1PbAs3S6. From structural and chemical data it was interpreted as the ordered structure of an
Sb-bearing relative of edenharterite, a postulation that meanwhile could be confirmed by the complete
structure determinations of both, edenharterite and jentschite (Berlepsch, 1996). Jentschite occurs in prismatic
crystals up to 2 mm length; it is opaque with a black metallic to submetallic luster, red translucent in thinfragments. Fracture is uneven to conchoidal, the mineral is extremely brittle, the cleavage along (i01) isperfect; the streak is dark red (darker than that of edenharterite). Mohs hardness is 2-2V2, according to a
microhardness VHN (10 g load) of 38-51 kg/mm z. The calculated density yields Dcalc = 5.24 g/cm 3.
The name is for Franz Jentsch (1868-1908) from Binn, a local 'Strahler' and for several years head of anearly Lengenbach syndicate that exploited the rare Lengenbach sulphosalt minerals at the beginning of thiscentury.
KEvwoRos: jentschite, T1-Pb-As-Sb-sulphosalt, new mineral, crystal data, microprobe analyses, Lengenbach,
Switzerland.
Introduction
IT was in 1904, that the name 'jentschite' was used
for the first time to describe an unknown sulphosalt
species from Lengenbach in Binntal (Koechlin,1904). Yet, shortly afterwards, the famous English
mineralogist R.H.Solly, the leading expert on

Lengenbach minerals at that time, stated that this'jentschite' was identical with a mineral described byhimself as a new species under the name lengenbachite (Solly, 1905). According to the rules of theCommission on New Minerals and Mineral Names,
I.M.A., the name of a mineral that was named
erroneously may be used again after a lapse of atMineralogical Magazine, Vol. 61, February 1997, pp. 131-137
9 Copyright the Mineralogical Society

132

S. GRAESER AND A. EDENHARTER

least 50 years since its first mention. Taking accountof the fact that the name 'jentschite' was never used
to officially describe a new mineral species, and thatits first mention was claimed by Solly to be erroneous
already in 1905, we did not hesitate to use the nameagain in order to honour the great merits of the local
expert of Lengenbach minerals, Franz Jentsch (18681908). As head of a 'Lengenbach syndicate' that
exploited the Lengenbach sulphosalt mineralisationin the period around 1900, he provided the numerous
mineralogists who were investigating the spectacularsulphosalt occurrence with carefully selected mineral
specimens, and many of the new mineral species
described from Lengenbach at that time wereprimarily discovered by him.
The first samples with the new mineral jentschitewere detected among material of the ordinary
exploitation collected for the 'Arbeitsgemeinschaft
Lengenbach' by Toni Imhof and his team in 1987.
Through this material an unmistakably new sulphosalt phase was recognized, yet, the polysynthicallytwinned crystals did not allow an unequivocal
determination of space group symmetry or of thecell parameters. It was some years later, in 1992, that
additional material was discovered that enabled athorough investigation of the new mineral which,however, fully confirmed all previous determinations
carried out on the mineral.
Jentschite, like other new TI-As-sulphosalts suchas edenharterite T1PbAsaS6 (Graeser and Schwander,1992), erniggliite TI2SnAs2S6 (Graeser et al., 1992),
and stalderite T1Cu(Zn,Fe,Hg)2As2S6 (Graeser et al.,1995), does not originate from the old classicalLengenbach site which was abandoned in 1987
because of dangerous exploitation and unattractive
material, hut from a new level that was inaugurated
in 1988, located farther to the North-East and about
25 m above the old quarry.
The proposal for the new mineral and its name wassubmitted to the Commission on New Minerals andMineral Names, I.M.A, for consideration (93-025).
They accepted the new mineral unanimously, thoughwith some critical remarks regarding the name. Typespecimens are preserved at the Natural History
Museum Basel, and at the Mineralogical Institute,
University of Basel.

Description
Physical and optical properties. A first sample
containing jentschite was found in 1987, the first yearthat the new Lengenbach site came into operation.
The appearance of the mineral was very similar tothat of edenharterite; the platy habit of the crystals,
however, pointed to a different mineral. From thesubsequent study of the unknown mineral, the close
relationship in particular to edenharterite but also toother Tl-sulphosalts was recognized. The similarityof these minerals in appearance, morphology andoptical properties makes it practically impossible todistinguish exactly the various Lengenbach T1sulphosalts from each other without X-ray diffraction
methods. Among the three most similar minerals
jentschite, edenharterite, hutchinsonite, the first has
the highest density, the darkest streak colour and thelowest hardness. In polished section jentschite yields
the highest reflectivity values and the most distinct
anisotropy effects (see Table 1). Different from theother minerals in this group, jentschite shows aperfect cleavage across the prismatic c-axis (along(101)). If trying to break one of the acicular crystals,
it always produces a clean cut along (i01) forming anangle of about 108 ~ with the c-axis.
Regarding the fact that jentschite is a completely
new Lengenbach mineral, the crystals achieve aremarkable size (~< 2 mm length). Like other T1minerals (erniggliite, stalderite) from Lengenbach,jentschite has remained an extremely rare species:
since its first discovery in 1987 (exhausted forinvestigation), one additional find o f five samples
in 1992 was made, though with numerous excellent
crystals. On the other hand, it may be pointed out thatthe closely related mineral edenharterite has been
discovered on far more than 100 samples in themeantime.
X-ray diffraction study. The powder diagram ofjentschite contains numerous characteristic diffraction lines which allow a quick and unequivocal
distinction from other closely related T1-Pb-Assulphosalts. The single-crystal study (Weissenberg
and Precession cameras) was very complicated forthe preliminary material from 1987 because all
crystals were polysynthetically twinned along (010)(albite twins). Finally, new excellent samples foundin 1992 provided better material. These crystals, too,
were all twinned but most of them appeared as
contact twins along (100) (gypsum twins, see Fig. 2)
from which single-crystal fragments could be
separated, though they strongly preferred to breakalong the perfect cleavage parallel to (101) thanbetween the two twins. The results of the renewed
study, however, fully confirmed the previously
collected data (Table 2).
In the course of the single-crystal study a strange
fact became obvious: photographs of the reciprocallattice along the planes a/b, and b/c, respectively,
were practically identical with the corresponding
planes of edenharterite; only the third section along
a/c was different, though in this case, too, a close
relation between the two structures was easily
recognizable.
Perhaps it should be mentioned that, comparedwith the original proposal for jentschite to theCommission on New Minerals and Mineral Names,

JENTSCHITE, A NEW SULPHOSALT MINERAL

133

TABLE 1. Physical and optical properties of some T1-As-sulphosalts from Lengenbach
Jentschite 1
Shape:
Twins:
Colour:Streak:Cleavage:
Hardness:
Density:long prismatic,
platy to acicular(010) albite twin(100) gypsum twin
brilliant black,
red internalreflections
dark red(101) perfect
2-2 895.24 g/cm3

Edenharterite 2

Hutchinsonite 3

short prismatic
to isometric
not observed

long prismatic,platy
not observedbrown to black,
red internalreflections
raspberry red(100) distinct
2%-3
5.09 g/cm 3

dark red to black,
red translucent
orange(010) imperfect
3 89
4.6-4.7 g/cm 3

Ore Microscopy (LEITZ MPV-compact microscope)
Reflectivity (measured in air, WTiC standard):
470 nm:29.7-35.4
543 nm:28.8-33.1
587 nm
26.7-30.3
657 nm:26.6-29.9

28.5-30.5
28.5-31.5
27.0-28.5
27.0-2930.0-31.0-

38-51 (10g)

95-101 (10g)170-171 (100g)

clearly visible

weak

distinct

Microhardness:

Anisotropy:

IJentschite TIPbAs2SbS6, Lengenbach (this paper)
2Edenharterite T1PbAs3S6, Lengenbach (Graeser and Schwander, 1992)
3Hutchinsonite T1PbAssS9, Lengenbach (Graeser, 1965)

the monoclinic cell has been changed and a cell witha smaller angle f~ has been chosen (001 ~ 101) ina g r e e m e n t with the structure d e t e r m i n a t i o n(Berlepsch, 1996).
Chemical composition. From preliminary EDS
investigations on the SEM the qualitative composition of the mineral as a T1-Pb-As-Sb-S-sulphosalt
could be derived. Quantitative analyses were carriedout on an ARL microbrobe (Table 3), from which theformula for jentschite could be calculated as
T1PbAs2SbIS6. The analyses were performed on
two individual crystals, partly as twins, partly as
random intergrowth. Though the variation between
the numerous analyses appears relatively small, it
must be pointed out that, compared with thetheoretical formula, the values for Pb and Sb arealways too low and that for As too high:
Edenharterite andjentschite. In 1992 we described
the new Tl-mineral edenharterite from the Lengen-bach quarry (Graeser and Schwander, 1992). The
single-crystal diffraction study (see above) of
jentschite revealed a conspicuous relationsshipbetween the structures of the two minerals, that was
additionally confirmed by the chemical analyses andthe mineral formula derived from them. The
respective data for the two mineral species arecompiled in Table 4. From these data arose thequestion on the nature of the relationsship, anessential problem before submitting the proposal to
the Commission on New Minerals and Mineral
Names, I.M.A., for consideration. From the fact thatboth minerals have an identical general formula but
clearly different crystal symmetry, it becomes
obvious that they cannot represent members of asolid-solution series (otherwise the new phase would
represent merely an Sb-bearing edenharterite within ahypothetical solid-solution series between edenharterite and a hitherto unknown Sb-edenharterite). The

134

S. GRAESER AND A. EDENHARTERTABLE 2. X-ray powder diffraction data of jentschite from Lengenbach
h k l

dc~

dobs

1/11

h k l

dcalc

dob s

1/11

02 0
1 10
0 1 1
1 0 1
0 2 1
14 0
04 1
06 0
2 10
1 1
2 1
14 1
24 0
i 6 1
2 50
0 7 1
1 16
26 0
0 1
23 1
04 2
25 1

11.984
7.365
5.426
5.358
5.052
4.738
4.080
3.995
3.819
3.712
3.585
3.317
3.250
3.203
3.0l 1
2.917
2.821
2.779
2.670
2.645
2.526
2.420

11.947
7.377
5.430
5.346
5.042
4.738
4.090
3.998
3.816
3.715
3.587
3.322
3.252
3.201
3.008
2.916
2.823
2.778
2.670
2.647
2.527
2.418

<10
<10
<10
32
12
19
26
74
54
<10
86
19
<10
<10
11
21
100
84
58
<10
<10
22

0 52
37 1
370
3 8 1

2.338
2.106
2.060
1.993

2.338
2.106
2.059
1.994
1.960
1.923
1.899
1.861
1.816
1.790
1.752
1.724
1.695
1.641
1.566
1.539
1.505
1.485
1.462
1.448
1.342
1.231

17
14
<10
<10
<10
<10
<10
<10
<10
<10
<10
<10
12
<10
<10
<10
<10
<10
<10
<10
<10
<10

Debye-Scherrer camera, 114.60 ram, Fe-K~ radiation
Single-crystal data:
Space group P21/n
a = 8.121(3) A
b = 23.969(9)13 = 107.68(3) ~c = 5.847(3)V = 1084.3(5) ~3
Lattice constants refined from the powder data
1/11 were determined densitometricallysingle-crystal data, on the other hand, exclude thepossibility of it being a polytypic mineral toedenharterite. Hence the minerals were interpreted
as homeotypes, in which the amount of Sb might beresponsible for the formation of the respective
mineral; small Sb-contents remain randomly distributed in a structure of orthorhombic symmetry yet,when exceeding a special threshold value, Sb
occupies a site of its own in an ordered monoclinic
structure. A comprehensive crystal-chemical andstructural investigation by Berlepsch (1996) clearlysupported this assumption.
On a Lengenbach sample sent to us for. determination just recently, one small crystal (0.5 mm length)
was investigated because of its uncommon appearance. During a Gandolfi study, the diffraction patternof the whole crystal was recorded, which, to our great
surprise, showed the characteristic diffraction lines ofboth minerals, edenharterite and jentschite. Therefore

the whole crystal was checked by single-crystal
methods, yet the result was not very helpful; the
X-ray films yielded exclusively the reflections of theorthorhombic phase edenharterite. As the crystal
must not be destroyed, it was subject to a SEM study.
Using the EDS device, the chemical composition, inparticular the As/Sb ratio, was determined by pointanalyses. All determinations were carried out on theflat (010) face in order to get highly reproducablevalues. The analyses prove that the crystal is nothomogeneous with respect to the As-Sb-contents, theextreme values reaching from T1PbAs2.65Sb0.35 to
T1PbAs2.sSb0.5 which is quite close to the formula ofjentschite (Table 3). Presumably the composition ofthis crystal corresponds almost exactly to somethreshold value between edenharterite and jentschite,provided that the transition from edenharterite tojentschite is controlled by nothing other than the As/
Sb-ratio.

JENTSCHITE, A NEW SULPHOSALT MINERAL

135

TA~LZ 3. Chemical composition of jentschite (wt.%)

T1
Pb
As
Sb
S
Total

I

II

23.90
21.52
19.30
12.40
22.53
99.65

23.76
21.16
19.44
12.21
22.63
99.20

III

IV

23.92 (23.47-23.98)
21.44 (20.67-21.48)
19.16 (17.91-20.88)
12.53 (10.66-14.94)
22.42 (21.87-22.83)
99.47

23.34
23.66
17.11
13.91
21.97
100.00

Structural formula (based on 11 atoms)
T1
Pb
As
Sb
S

1.00
0.89
2.21
0.87
6.03

1.00
0.87
2.22
0.87
6,03

1.01
0.89
2.20
0.89
6.02

1.00
1.00
2.00
1.00
6,00

I, II mean of 3 analyses on individual crystals
III mean of 15 analyses (with ranges)
IV theoretical composition for T1PbAs2Sb1S6
ARL microprobe (20 kV, 20 nA)
Standards: T1AsS2 (T1,As,S), galena (Pb,S), stibnite (Sb)Morphology. The first find of jentschite in 1987
provided one almost perfect crystal (Fig. 1) of about
0.4 mm length which, besides X-ray diffraction work,
was subject to a measurement on the opticalgoniometer. As can be seen from the SEM picture,
the crystal is polysynthetically twinned along {010}(albite twins). Though the small size of the crystal
was quite cumbersome for this purpose, the measured
values permitted an unequivocal indexing of thefaces (Fig. 2). Whereas in the case of jentschite
isolated crystals are quite common, the mineral

Fro. 1. SEM picture of jentschite: the polysynthetic
twinning of the crystal is clearly visible. The cleavage
along (i01) is indicated by striations parallel to this face.

edenharterite occurs only in aggregates composed ofextremely small single crystals, of mostly less than
0.2 mm, that were not suitable for goniometricmeasurements. Actually, the crystal of Sb-bearing
edenharterite described above represents a unique
isolated edenharterite crystal known so far. Therefore
this crystal, too, was measured goniometrically anddrawn by the SHAPE program. Comparison of thetwo crystal drawings clearly shows the closemorphological relationship between jentschite andedenharterite.
Occurrence. Jentschite is one of the numerous
members of sulphosalts occurring in small roundedcavities (druses) of the Triassic dolomite at
Lengenbach in Binntal (Fig. 3). Moreover, it belongs
to the group of Tl-sulphosalts like edenharterite,
stalderite, erniggliite, hatchite, wallisite, hutchinsonite, and some additional species at this time not yet
clearly identified, that obviously became enrichedwithin the uppermost part of the dolomite outcrop.
They are unequivocally products of hydrothermal
activity during a last stage of the formation ofminerals in the Binntal dolomite. T1 and As originate
from a tectonically underlying series of gneisses andwere remobilised by either Alpine metamorphism(Graeser, 1965), or by an earlier event (Knill, 1995).
Acknowledgements

Our sincerest thanks go to the chairman of theCommission of New Minerals and Mineral Names,

136

S. GRAESERAND A. EDENHARTER
041

i01

~01
~01

001

u

3.12.1~ ~

171
7

1

51

481~

I
2.14.1

010

ii0

--

130

010

130

a

b

i

/130

I

010

i

C

FIG.2. Morphologyofjentschite and edenharterite. (a)jentschite habit, usuallytwinned along (010) (albite twin); (b)edenharterite crystal; (c) jentschite twinned along (100) (gypsum twin).
Dr. J.A. Mandarino (now emeritus), for his helpful provided the unique sample with Sb-bearing edensuggestions, especially regarding the naming of the harterite. We are greatly obliged to R. Guggenheim,
mineral. Mr Ralph Cannon (Kassel, Germany) kindly D. Mathys, and M. DSggelin (SEM laboratory,JENTSCHITE, A NEW SULPHOSALT MINERAL137

TABLE 4. Relations between edenharterite and jentschite
Edenharterite ~Jentschite 2

FormulaTIPbAs3S6

T1PbAs2SblS6

Crystal system
Space group
Cell parameters

orthorhombic
Fdd2
15.465 ,&47,5075.843
90 ~
0.326:1:0.123
0.328:1:0.123

monoclinic
P211n
8.121
23.9695.847
107.68 ~0.339:1:0.244 (X-ray)0.339:1:0.246 (goniom.)

a

~

b=
C-~

B=

a:l:c=
Cell volumeV=4292 ~3(= 4.1073)

1084 ~3

Cell content

Z =

16

4

1 Graeser and Schwander (1992)
2 this paper

Fro. 3. Type specimen of jentschite with typical gypsum
twinned crystal. The largest crystal has a length of 2mm. Photograph by W. Gabriel.

University of Basel) for their help in performing
SEM pictures and chemical analyses of the minerals(especially the Sb-bearing edenharterite). The
Arbeitsgemeinschaft Lengenbach, the syndicate
exploiting the Lengenbach minerals for scientificresearch, kindly put the required material at our
disposal.
References

Berlepsch, P. (1996) Crystal structures and crystal

chemistry of edenharterite (TIPbAs~S6) andjentschite (TIPbAszSbS6). Schweiz.Mineral.
Petrogr. Mitt., 76 (in press).
Graeser, S. (1965) Die Mineralfundstellen ira Dolomit
des Binnatales. Schweiz.Mineral. Petrogr. Mitt., 45,
597.
Graeser, S. and Schwander, H. (1992) Edenhartedte(TIPbAs3S6): a new mineral from Lengenbach,
Binntal (Switzerland). Eur. J. Mineral., 4, 1265-70.
Graeser, S., Schwander, H., Wulf, R. and Edenharter, A.
(1992) Erniggliite, (T12SnAs2S6), a new mineralfrom Lengenbach, Binntal (Switzerland): description
and crystal structure determination based on datafrom synchrotron radiation. Schweiz. Mineral.
Petrogr. Mitt., 72, 293-305.
Graeser, S., Schwander, H., Wulf, R. and Edenharter, A.
(1995) Stalderite T1Cu(Zn,Fe,Hg)2As~S6 - - a newmineral related to routhierite: description and crystal
structure determination. Schweiz. Mineral. Petrogr.
Mitt., 75, 337-45.
Knill, M. (1995) Geochemistry and genesis of thepolymetallic Lengenbach mineralization, Binn
Valley, Switzerland. PhD. thesis, ETH Ziirich,(unpubl.)
Koechlin, R. (1904) Ausstellung: Mineralien aus dem
Binnental. Tschermaks Mineral. Petrogr. Mitt., 23,551-2.
Solly, R.H. (1905) Some new minerals from the
Binnenthal. Mineral. Mag., 14, 72-82.

[Manuscript received 5 June 1996]