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The new mineral challacolloite, KPb2Cl5, the natural occurrence of a technically known laser material

Authors:
  • Mineralogical Museum Hamburg

Abstract and Figures

The new mineral challacolloite has the ideal chemical formula KPb2Cl5. The type locality of challacolloite is the Challacollo silver mine SE of Iquique, Atacama desert, northern Chile. In the year of discovery challacolloite was also found on leucotephrite lava from the Vesuvius eruption of May 1855. It occurs closely associated with cotunnite as a hydrothermal phase (Chile) or as the product of fumarole activities (Italy). Challacolloite is colourless to white with an adamantine luster. Mohs's hardness is about 2–3. The calculated density is 4.77 g/cm3. Challacolloite is biaxial (+), 2 Vcalc = 67° with nα = 2.004(2), nβ = 2.010(2) and nγ = 2.024(3). Chemical analyses of the type material give (wt.%) K 5.45, Pb 66.30, Cl 28.69. Challacolloite is monoclinic with space group P21/c. Cell parameters refined from powder diffraction data of the type material are a = 8.864(8), b = 7.932(8), c = 12.491(11) (Å), β = 90.153(5)°, V = 878.2(1) Å3 with Z = 4. Challacolloite is isotypic with NH4Pb2Cl5 and PbU2Se5. Synthetic REE-doped equivalents of challacolloite are known as technical laser materials. The strongest reflections in the X-ray powder diffraction data of the type material are as follows [dmeas. (Å)(I, hkl)]: 3.686 (100, 211), 3.609(49, 20–2), 2.669(42, 22–2), 8.855(39, 100) and 3.961(31, 020). The mineral was named after its type locality.
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N. Jb. Miner. Abh.
2005, Vol.182/1, p. 95–101, Stuttgart, November 2005, published online 2005
by E. Schweizerbart’sche Verlagsbuchhandlung 2005
The new mineral challacolloite, KPb2Cl5, the natural
occurrence of a technically known laser material
Jochen Schlüter and Dieter Pohl, Hamburg, Germany, and Sergey Britvin, St. Petersburg
Russia
With 2 figures and 4 tables
Abstract: The new mineral challacolloite has the ideal chemical formula KPb2Cl5. The type locality of challacolloite is the Chal-
lacollo silver mine SE of Iquique, Atacama desert, northern Chile. In the year of discovery challacolloite was also found on leu-
cotephrite lava from the Vesuvius eruption of May 1855. It occurs closely associated with cotunnite as a hydrothermal phase
(Chile) or as the product of fumarole activities (Italy). Challacolloite is colourless to white with an adamantine luster. Mohs’s
hardness is about 23. The calculated density is 4.77 g/cm3. Challacolloite is biaxial ( +), 2 Vcalc =67˚ with nα=2.004 (2), nβ=
2.010 (2) and nγ=2.024 (3). Chemical analyses of the type material give (wt.%) K 5.45, Pb 66.30, Cl 28.69. Challacolloite is mo-
noclinic with space group P21/c. Cell parameters refined from powder diffraction data of the type material are a=8.864 (8), b=
7.932 (8), c=12.491 (11) (Å), β=90.153 (5)˚, V=878.2 (1) Å3with Z=4. Challacolloite is isotypic with NH4Pb2Cl5and
PbU2Se5. Synthetic REE-doped equivalents of challacolloite are known as technical laser materials. The strongest reflections in
the X-ray powder diffraction data of the type material are as follows [dmeas.(Å)(I, hkl)]: 3.686 (100, 211), 3.609 (49, 202),
2.669(42, 222), 8.855 (39, 100) and 3.961(31, 020). The mineral was named after its type locality.
Key words: Challacolloite, new mineral, cotunnite, potassium lead chloride, Chile, Atacama desert, Challacollo mine, Vesuvius
volcano, IR-laser.
Introduction
The type locality of the new mineral challacolloite is the
famous Chilean silver mine Challacollo (S 20˚ 57,W
69˚ 21), which is situated in the Atacama desert about
130 km southeast of Iquique. The argentiferous deposit,
of the epithermal-epigenetic type, is bound to fissure
veins and genetically related to acid intrusions of an
acidic to intermediate subvolcanic complex of Upper
Cretaceous to Lower Tertiary age (Botto 1975, Car-
rasco &Chong 1985). Challacolloite was discovered
on mine dumps by Arturo Molina, Iquique, in 2003.
In the same year challacolloite was found by one of the
authors (S. B.) on an old museum specimen from the Mi-
neralogical Museum, Saint Petersburg State University,
collected at the Vesuvius volcano, Naples, Campania,
Italy, labelled as cotunnite. Challacolloite here occurs in
cavernous leucotephrite lava from the eruption of May 1,
1855. Further natural occurrences of potassium lead
chloride are reported from the Kudryavyi volcano, Iturup
Island, Kuril Islands (Tkachenko et al. 1999) and the
Satsuma-Iwojima volcano, Japan (Africano et al.
2002). Meanwhile challacolloite was found also on other
Vesuvian “cotunnite samples” from different eruptions
(e. g. the eruption of 1907) in the collection of the Mine-
ralogical Museum, University of Hamburg.
Synthetic analogues of challacolloite doped with
REE3+cations are well-studied due to their technical
usage. They serve as promising new laser host crystals
for mid-IR solid-state laser and might also be efficient
candidates for room-temperature up-conversion laser in
the visible region (Virovets et al. 2001, Isaenko et al.
2001, Roy et al. 2003).
The new mineral and its name were approved by the
IMA Commission on New Minerals and Mineral Names
in December 2004 (No. 2004-028). The name of the min-
DOI: 10.1127/0077-7757/2005/0033 0077-7757/05/0033 $ 1.75
2005 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart
96 J. Schlüter et al.
Fig. 1. Colourless challacolloite-cotunnite-masses with high lustre and tiny blue inclusions of “percylite” associated with glassy uklons-
kovite crystals and acicular crystals of hemimorphite. The vug is lined with a white band of fluorite (width of the picture: 22mm; K.-C.
Lyncker photo). This picture of challacolloite and associated minerals can be found on our homepage (http://www.rrz.uni-hamburg.de/
mpi/museum) in colour.
eral is for the type locality. Type material is preserved in
the collection of the Mineralogical Museum of the Uni-
versity of Hamburg, Germany.
Appearance and physical data
At the Challacollo mine challacolloite occurs closely in-
tergrown with cotunnite (PbCl2), “percylite” (a poorly
defined PbCu Cl mineral, probably a mixture of bo-
léite and pseudoboléite) and uklonskovite [NaMg(SO4)F
·2H
2O], associated with hemimorphite, caracolite (Na3
Pb2(SO4)3Cl), anglesite, nitratine, anhydrite and fluorite
in quartz vugs (Fig. 1). The aggregates of challacolloite
with cotunnite reach 4 mm in size, but the two minerals
are intergrown on a micron-scale (Fig. 2). In effusive
rocks of the Vesuvius volcano, challacolloite is asso-
ciated with cotunnite as well. Here challacolloite occurs
in crusts and as botryoidal aggregates up to 0.5 mm thick
covering cavernous leucotephritic lava. The aggregates
possess columnar to spherulitic structure and consist of
subparallel intergrowths of curved lamellae, 2 –5 µm
wide and up to 50 µm long, elongated probably parallel
to [100].
Challacolloite is soft, with a Mohs’s hardness of about
23. It is colourless to white with a white streak, its te-
nacity is brittle and the fracture subconchoidal. The lus-
ter is adamantine on fresh surfaces to greasy when
Fig. 2. Backscattered electron image showing uklonskovite
(NaMg(SO4)F · 2 H2O; dark grey to black) with challacolloite
(KPb2Cl5; light grey) and cotunnite (PbCl2; white).
longer exposed to the atmosphere. There is no obser-
vable fluorescence. Challacolloite is soluble in water and
dilute hydrochloric acid. The calculated density based on
the empirical formula is 4.77g/cm3and 4.76g/cm3for the
material from Chile and Italy, respectively. The infrared
spectrum between 400 and 3800 cm–1 shows no absorp-
tion bands. Challacolloite is biaxial (+), 2 Vcalc =67˚
The new mineral challacolloite 97
with nα=2.004 (2), nβ=2.010 (2), nγ=2.024 (3) for
589 nm using a solution of realgar, sulfur and selenium
in AsBr3for n >2.01 and realgar and sulfur for n >1.810
and <2.01, respectively. Z coincides with the elongation
of the lamellae. Due to small size and curvature of the
challacolloite lamellae it was not possible to measure
some optical properties of the mineral, i. e. 2 V and pre-
cise optical orientation. Raman spectra and elastic pro-
perties have been measured for synthetic KPb2Cl5crys-
tals grown by the Bridgman-Stockbarger technique by
Vtyurin et al. (2004).
Chemical composition
Electron microprobe analyses of challacolloite were ob-
tained in Hamburg on Chilean material on 8 points and
in St. Petersburg on Italian material on 7 points (Table 1).
The overall chemical analyses gave the following
ranges: (wt.%) K 5.3 –6.6, Pb 65.5 –67.0 Cl 27.828.9.
Analyses were obtained in Hamburg with a Cameca
electron microprobe (CAMECA SX 100) operating in
the wavelength-dispersion mode with an accelerating
voltage of 15 kV, a specimen current of 10 nA and a
beam diameter of 10 µm. The standards used were ortho-
clase and vanadinite. St. Petersburg analyses were ob-
tained with a Link ISIS energy-dispersion system, 20 kV,
1 nA, 3 µm beam diameter, using cotunnite and micro-
cline as standards. These analyses (Table 1) led to empir-
ical formula of K0.88Pb2.02 Cl5.00 (based on 5 anions,
Hamburg) or K1.02Pb2.00Cl4.98 (based on 8 atoms per for-
mula unit, St. Petersburg), which can be simplified to
KPb2Cl5. No other elements with atomic number greater
than 4 were found in the mineral. In addition, no NH4+
was detected by infrared spectroscopy and Nessler’s test.
Table 1. Chemical composition of challacolloite from Chile and
Italy.
Challacollo, Ideal Vesuvius vol-
Chile* wt.% cano, Italy**
Constituent wt.% Range wt.% Range
K 5.45 5.325.57 6.20 6.4 6.2– 6.6
Pb 66.30 66.1966.99 65.70 66.1 65.566.6
Cl 28.69 28.5428.92 28.10 28.2 27.828.7
Total 100.44 100.00 100.7
Probe standards: * Hamburg: orthoclase, vanadinite; ** St. Peters-
burg: microcline, cotunnite.
Table 2. Fractional positional coordinates of challacolloite (Chile)
with standard uncertainties in parentheses. An overall temperature
factor of 2.63(7) Å2was applied. All sites are fully occupied.
xyz
K 0.0151(36) 0.0429(28) 0.8295 (17)
Pb1 0.5054 (12) 0.9863 (9) 0.1736(3)
Pb2 0.2449(5) 0.9353(4) 0.4937 (6)
Cl1 0.0413(32) 0.3082 (31) 0.0715 (20)
Cl2 0.4660(35) 0.3455 (30) 0.1011 (19)
Cl3 0.2555(43) 0.1471 (28) 0.3110 (19)
Cl4 0.2728(23) 0.5306 (20) 0.4873 (28)
Cl5 0.2175(36) 0.6941 (28) 0.2195 (12)
X-ray crystallography
Challacolloite is monoclinic with space group P21/c. The
X-ray powder diffraction patterns (Table 3) were ob-
tained in Hamburg using a Philips X’Pert powder dif-
fractometer with Cu Kαradiation (graphite secondary
monochromator) at 40 kV/30 mA, in St. Petersburg with
a DRON-2 diffractometer with Co Kα-radiation (quartz
monochromator) at 35 kV/20 mA. The unit-cell param-
eters refined from X-ray powder diffraction data are a=
8.864 (8), b=7.932 (8), c=12.491 (11) (Å), β=
90.153 (5)˚, V=878.2 (1) Å3and a=8.887 (2), b=
7.939(1), c=12.489(2) (Å), β=90˚, V=881.1(5) Å3for
Chilean and Italian material, respectively. For the latter
material the monoclinic angle βwas fixed to 90˚ because
in this case we did not perform a Rietveld refinement.
From the mere peak positions in the powder diagram it is
impossible to obtain an angle different from 90˚ as there
are no splitted peaks resulting from the monoclinicity.
The number of formula units per unit cell is four.
Single-crystal X-ray studies could not be carried out.
Several attempts to obtain single-crystal data were un-
successful due to small size or curvature of challacolloite
lamellae.
A X-ray diffraction diagram of a powder from Chi-
lean material, which unavoidably contained challacol-
loite, cotunnite, uklonskovite and quartz was measured
and evaluated by Rietveld refinement performed with the
program DBWS (Young et al. 1995). The 2θ-range of
the measured pattern was 7.00 to 90.00˚, step scan 0.02˚
and measuring time 4 s. The reflections were extracted
from the powder pattern using the program DB2 dI
(Smith &Young 1998). For cotunnite, uklonskovite and
quartz the positional coordinates of the well-known
structures were used as fixed parameters in the refine-
ment, whereas for challacolloite the positional coordina-
tes of NH4Pb2Cl5(Ras et al. 1977) served as a starting set
98 J. Schlüter et al.
Table 3. X-ray powder diffraction data: comparison of challacolloite from Chile, Italy (monoclinic) and synthetic KPb2Cl5(ortho-
rhombic indices).
Chile* Italy** synthetic KPb2Cl5***
Id(obs) d(calc) hk l I d(obs) d(calc) hkl I d(obs) hkl
39 8.855 8.864 10 0 100 8.88 8.887 1 0 0 25 8.83 1 0 0
12 6.681 6.696 0 1 1 14 6.71 6.700 0 1 1 11 6.69 0 1 1
5 6.240 6.245 0 0 2 7 6.25 6.245 0 0 2 5 6.25 0 0 2
8 5.900 5.911 1 1 0 19 5.92 5.921 1 1 0 7 5.90 1 1 0
14 5.335 5.346 1 1 1 11 5.34 1 1 1
5.339 1 1 1
10 5.097 5.099 1 0 2 14 5.11 5.109 1 0 2, 1 0 2 10 5.10 1 0 2
5 4.293 4.289 1 1 2 10 4.295 4.296 1 1 2, 1 1 2 7 4.292 1 1 2
4.297 2 1 1
31 3.961 3.966 0 2 0 44 3.970 3.970 0 2 0 25 3.968 0 2 0
100 3.686 3.693 2 1 1 99 3.699 3.703 2 1 1, 2 1 1 100 3.693 2 1 1
3.687 0 1 3 3.687 0 1 3
49 3.609 3.619 2 0 – 2 71 3.621 3.624 1 2 0 40 3.616 2 0 2
3.610 2 0 2 3.620 2 0 2, 2 0 2
6 3.478 3.476 1 2 1 13 3.481 3.481 1 2 1, 1 2 1 8 3.478 1 2 1
13 3.400 3.407 1 1 3 13 3.410 3.405 1 1 3, 1 1 3 9 3.406 1 1 3
3.401 1 1 3 3.350 0 2 2 2 3.350 0 2 2
6 3.294 3.294 2 1 2, 2 1 2
3 3.124 3.131 1 2 2 10 3.130 3.135 1 2 2, 1 2 2 5 3.129 1 2 2
3.123 0 0 4 3.122 0 0 4 3 3.123 0 0 4
5 2.951 2.955 3 0 0 12 2.959 2.962 3 0 0 4 2.952 3 0 0
4 2.907 2.906 0 1 4 8 2.904 2.906 0 1 4 4 2.907 0 1 4
10 2.873 2.877 2 2 1 13 2.882 2.881 2 2 1, 2 2 1 11 2.876 301
2.875 2 2 1
6 2.830 2.831 2 1 3 8 2.836 2.837 2 1 3, 2 1 3 6 2.836 2 1 3
7 2.772 2.769 3 1 0 11 2,774 2.775 3 1 0 9 2.764 1 1 4
11 2,762 2.762 1 1 4, 1 1 4
9 2.729 2.730 1 2 3 10 2.733 2.734 1 2 3, 1 2 3 9 2.733 1 2 3
2.733 1 2 – 3
42 2.669 2.673 2 2 2, 3 0 – 2 57 2.676 2.676 3 0 2, 3 0 2 50 2.671 3 0 2
2.670 2 2 2 2.675 2 2 2, 2 2 2
4 2.585 2.587 0 3 1 7 2.588 2.589 0 3 1 5 2.587 0 3 1
18 2.548 2.550 2 0 4 24 2.554 2.555 2 0 4, 2 0 4 20 2.553 2 0 4
2.556 4 2 0 17 2.539 2.536 3 1 2, 3 1 2
9 2.532 2.534 1 3 0 2.536 1 3 0 9 2.534 1 3 0
2.529 3 1 2
3 2.482 2.483 1 3 1 5 2.483 2.486 1 3 1, 1 3 1 2 2.483 1 3 1
4 2.455 2.454 0 2 4 2 2.454 0 2 4
2.437 0 3 2
3 2.363 2.363 1 2 4, 3 2 0 7 2.374 2.374 3 2 0 4 2.371 3 2 0
13 2.346 2.347 1 3 2 20 2.350 2.350 1 3 2, 1 3 2 14 2.350 1 3 2
2.348 2 1 3
6 2.327 2.327 3 2 1 12 2.332 2.332 3 2 1, 3 2 1 7 2.328 3 2 1
2.329 1 3 2
9 2.301 2.303 3 1 3 11 2.307 2.309 3 1 3, 3 1 3 10 2.303 1 1 5
2.300 1 1 5 2.301 1 1 5, 1 1 5
23 2.233 2.237 2 3 1, 2 3 1
13 2.231 2.232 0 3 3 2.233 0 3 3 18 2.232 0 3 3
13 2.215 2.216 4 0 0, 3 2 2 45 2.220 2.222 4 0 0 16 2.216 3 2 2
2.219 3 2 2, 3 2 2
4 2.163 2.165 1 3 3 8 2.166 2.166 1 3 3, 1 3 3 6 2.166 1 3 3
2.164 1 3 3
8 2.148 2.145 2 2 4 10 2.149 2.148 2 2 4, 2 2 4 8 2.148 2 2 4
2.137 2 3 2, 2 3 2
2.109 4 1 1, 4 1 1
The new mineral challacolloite 99
Table 3. Continued.
Chile* Italy** synthetic KPb2Cl5***
Id(obs) d(calc) hk l I d(obs) d(calc) hkl I d(obs) hkl
16 2.095 2.096 2 1 5 20 2.100 2.100 2 1 5, –2 1 5 19 2.101 2 1 5
4 2.081 2.082 0 0 6 8 2.082 2.082 0 0 6 7 2.083 0 0 6
2.074 3 1 4, 3 1 4
5 2.056 2.057 1 2 5 2.057 1 2 5, 1 2 5
2.057 3 2 3 9 2.063 2.062 3 2 3, 3 2 3 5 2.059 3 2 3
4 2.026 2.027 1 0 6, –1 0 6 3 2.027 1 0 6
2 1.992 1.995 2 3 3 4 1.995 1.995 2 3 3, 2 3 3
1.992 2 3 3 3 1.994 2 3 3
1.985 0 4 0
8 1.970 1.974 3 3 0
5 1.965 1.967 1 3 4 1.969 1 3 4, 1 3 4 7 1.968 1 3 4
6 1.934 1.935 4 2 0 13 1.938 1.939 4 2 0 9 1.935 4 2 0
3 1.911 1.912 1 4 1, 4 2 1 7 1.915 1.914 1 4 1, 1 4 1 5 1.912 4 2 1
9 1.899 1.901 4 1 3 17 1.903 1.903 4 1 3, 4 1 3 13 1.900 4 1 3
1.897 4 1 3
4 1.878 1.880 3 3 2 8 1.882 1.882 3 3 2, 3 3 2 6 1.879 3 3 2
1.878 3 3 2
5 1.848 4 2 2
8 1.842 1.843 0 2 6 8 1.844 1.843 0 2 6 9 1.845 0 2 6
1.838 2 3 4, 2 3 4
4 1.810 1.810 2 4 0 7 1.811 1.812 2 4 0 5 1.810 2 4 0
4 1.804 1.806 1 2 6 1.805 1 2 6, 1 2 6 3 1.805 1 2 6
1.809 4 0 4 1.810 4 0 4, 4 0 4
1.793 2 4 1, 2 4 1
3 1.781 1.782 3 3 3 4 1.781 3 3 3
1.780 3 3 3
1.765 4 1 4, 4 1 4
2 1.754 1.754 1 4 3 5 1.758 1.756 1 4 3, 1 4 3 3 1.756 501
1.755 1 4 3
5 1.741 1.740 2 4 2, –2 4 2 3 1.740 2 4 2
4 1.719 1.721 3 2 5, –3 2 5 2 1.680 2 3 5
1.718 5 1 1, 5 1 1
1.703 3 0 6, 3 0 6
2 1.667 1.665 3 3 4 4 1.669 1.668 3 3 4, 3 3 4 3 1.6679 5 1 2
2 1.6467 3 4 0
*: Data Hamburg: Philips X’Pert diffractometer, CuKα-radiation (graphite secondary monochromator), 40kV, 30 mA; ** data St. Peters-
burg: DRON-2 diffractometer, CoKα-radiation (quartz monochromator), 35kV, 20 mA; ***: JCPDS 271364 (Morris et al. 1976).
of refinable parameters. Then, using an overall temper-
ature factor for the atoms in each structure the Rietveld
refinement converged straight forward to Rwp =9.48.
The positional coordinates of challacolloite derived
from this refinement are given in Table 2. Compared to
the single-crystal structure determination on synthetic
material (Virovets et al. 2001), the structure of the min-
eral shows only moderate deviations. The parameters of
KPb2Cl5could have been used as a starting set as well
with the same result as those of NH4Pb2Cl5. However,
these data can be neither easily found in literature nor
compared with related structures. Comparison is difficult
because the choice of cell, origin and asymmetric unit all
differ from those given in other investigations. More-
over, the labeling of the chlorine atoms is completely
different too.
Discussion
The structure of challacolloite is isotypic to the struc-
tures of NH4Pb2Cl5(Ras et al. 1977) and PbU2Se5(Po-
tel et al. 1975) and is homeotypic to those of the ortho-
rhombic compounds U3Se5(Moseley et al. 1972) and
U3S5(Potel et al. 1972). As has been worked out by Po-
tel et al. (1975) a special feature of this structure type is
that it contains both coordination polyhedrons of lead
and uranium, namely, a seven-coordinated monocapped
100 J. Schlüter et al.
Table 4. Comparison of crystal data for challacolloite from Chile and Italy with synthetic KPb2Cl5[Virovets et al. 2001 and Morris et
al. 1976 (JCPDS 27-1364)].
Challacolloite, Chile Challacolloite, Italy KPb2Cl5* KPb2Cl5**
Reference This study This study Virovets et al. (2001) Morris et al. (1976)
(JCPDS 27-1364)
Crystal System Monoclinic Monoclinic Monoclinic Orthorhombic
Space Group P21/c P21/c P 21/c not given
a(Å) 8.864(8) 8.887(2) 8.854 8.865
b(Å) 7.932(8) 7.939(1) 7.927 7.934
c(Å) 12.491(11) 12.489 (2) 12.485 12.498
β
(˚) 90.153 (5) 90.00 90.05 90.00
V3) 878.2 881.1 876.3 879.0
Z444 4
D(calc) (g/cm3) 4.77 4.76 4.78 4.77
Strongest lines of powder diffraction pattern
Idhkl Idhkl Idhkl Idhkl
39 8.86 1 0 0 100 8.88 1 0 0 42 8.854 1 0 0 25 8.83 1 0 0
31 3.961 0 2 0 44 3.970 0 2 0 19 3.964 0 2 0 25 3.968 0 2 0
100 3.686 2 1 1 99 3.699 2 1 1 100 3.688 2 1 1 100 3.693 2 1 1
49 3.609 2 0 – 71 3.621 1 2 0 39 3.613 1 2 0 40 3.616 2 0 2
42 2.669 2 2 – 57 2.676 3 0 2 43 2.669 3 0 2 50 2.671 3 0 2
18 2.548 2 0 4 24 2.554 2 0 4 25 2.551 2 0 4 20 2.553 2 0 4
16 2.095 2 1 5 45 2.220 4 0 0 19 2.213 4 0 0 19 2.101 2 1 5
* Pattern calculated using author’s data.
** Cell setting transformed to that of Virovets et al. (2001), transformation matrix (100/001/0 –10).
octahedron and an eight-coordinated bicapped trigonal
prism. In the binary compounds the octahedron is lo-
cated on a mirror plane, whereas there are two trigonal
prisms being mirror-images one from another. On the
contrary these two trigonal prisms are centered by differ-
ent cations in the ternary compounds thus breaking the
mirror symmetry. Therefore, on going from the binary
compounds to the ternary ones, the symmetry is reduced
by the loss of a mirror plane resulting in a change from
the orthorhombic space group Pnma to its monoclinic
subgroup P1121/a(P121/c1). The unit-cell parameters are
still pseudo-orthorhombic (β90˚).
Acknowledgements
The authors thank Arturo Molina (Iquique, Chile) and
Maurizio Dini (La Serena, Chile) for providing the
Chilean samples used in this study. Thanks are due to
Mrs. S. Heidrich (Min.-Petr. Institut, Universität Ham-
burg, Germany) for performing microprobe analyses,
Mr. J. Ludwig (Min.-Petr. Institut, Hamburg) for X-ray
powder diffraction and Mr. J. Hartmann (Geol.-
Paläont. Institut, Universität Hamburg, Germany) for
SEM/EDX studies. Special thanks are due to Mr. K.-C.
Lyncker (Hamburg, Germany) for the specimen photo.
We thank Galina Anastasenko, the curator of the Mi-
neralogical Museum, St. Petersburg State University, for
the Italian specimens provided for this study.
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Received: April 12, 2005; accepted: July 18, 2005
Responsible editor: A. Beran
Authors’ addresses:
Dr. Jochen Schlüter and Prof. Dr. Dieter Pohl, Mineralogisch-Petrographisches Institut der Universität Hamburg, Grindelallee 48,
D-20146 Hamburg, Germany. E-mail: jochen.schlueter@uni-hamburg.de
Sergey N. Britvin, Department of Mineral Deposits, St. Petersburg State University, Universitetskaya Nab. 7/9, RU-199034 St. Peters-
burg, Russia. E-mail: sergey_britvin@mail.ru
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