E
N. Jb. Miner. Abh. (J. Min. Geochem.) 193/1 (2016), 59–68
Published online September 2015; published in print January 2016
Article
The chemical composition of uranospathite, arsenurano­s­pathite, and associated minerals revisited: the peculiarity of
fluorine incorporation in autunite group minerals
Thomas Theye, Kurt Walenta, Gregor Markl
With 4 figures and 3 tables
Abstract: In contrast to most or all other members of the autunite group (“uranium micas”), the Al-bearing members uranospathite
and arsenuranospathite can contain F. To investigate the content of fluorine and its relation with other ions, the compositions of
these minerals from their respective type localities and of related minerals were analyzed with the electron microprobe.
The analyses of uranospathite from Redruth, Cornwall, show that all analyzed crystals contain F, however, in variable amounts
from 0.3 to 1.0 F per formula unit. The F content of the analyzed arsenuranospathite crystals is also variable, amounting from 0.2 to
1.0 F per formula unit. The average value for samples from Wittichen (Black Forest, Germany), one of the type localities, is 0.4 F
per formula unit. In the second type locality, Menzenschwand (Black Forest, Germany), a higher mean value of 0.9 F per formula
unit was analyzed. The incorporation of (OH) is necessary to achieve charge balance.
In general, the analyses of uranospathite and arsenuranospathite show a relatively consistent Al content of 0.8 to 1.0 Al per
formula unit. In contrast, the F content is stronger variable, between 0.2 and 1.0 F per formula unit. Therefore, the presented analyses are not compatible with an ideal coupled exchange involving Al and F as suggested for uranospathite by Locock et al. (2005),
and the IMA-approved formula Al1 -x□x[(UO2)(PO4)]2(H2O)20 + 3x F1 – 3x, 0 < x < 0.33 has therefore to be reconsidered. Also the ideal
formula of arsenuranospathite proposed by Chukanov et al. (2009), Al[(UO2)(AsO4)]2F * 20H2O, does not conform to this mineral
in general. We propose new simplified formulae which account for an independent variability of Al und of F.
Chemical analyses of a related Al-rich member of the autunite group, sabugalite, from two type localities in Portugal, revealed
that F is not present in significant amounts. The same is true for other analyzed autunite group minerals, even if associated with
either uranospathite or arsenuranospathite. It seems that the presence of F in substantial amounts is restricted to aluminum-bearing
and water-rich members of the autunite group.
Key words: Uranospathite, arsenuranospathite, autunite group, fluorine, electron microprobe analyses, Black Forest
been the subject of many studies. It is a remarkable history fraught with mistakes and inconsistencies, and it took
a long time until the true composition of the mineral was
ascertained. In the description of 1915, the composition
of uranospathite remained unknown. The symmetry was
assumed to be orthorhombic. The mineral was catalogued
as autunite, but some properties, such as the refractive
indices, distinguished it from this mineral and it seemed
reasonable to consider it a distinct species.
A subsequent investigation of uranospathite was performed by Frondel (1951). He cites a semiquantitative
spectrographic analysis of a type specimen by Annell and
Valentine which reveals that U, As, and P are the main
constituents, with As > P, whereas Cu and Fe are present
in small amounts only. Furthermore Frondel quotes an
Introduction
Uranospathite and arsenuranospathite belong to the autunite family with the general formula A(UO2)2[(P,As)O4]2
* nH2O. The A position can contain different monovalent
and trivalent but mostly bivalent cations such as Mg, Ca,
Fe, Co, Ni, Cu, and Ba (Walenta 1965, Locock 2007).
The H2O content in these minerals with bivalent A cations
is maximal n = 12. Uranospathite and arsenuranospathite,
in contrast, contain Al3+ in the A position, and (OH) and/
or fluorine is required for charge balance. In addition,
these members have a significantly higher H2O content
of n = 20.
Uranospathite which was described as a new species
from Redruth, Cornwall, by Hallimond (1915) has since
© 2015 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany
DOI: 10.1127/njma/2015/0292
www.schweizerbart.de
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T. Theye et al.
analysis by Gonyer of a non-type sample, supposed to be
identical with the original material, which gave a composition close to that of zeunerite: Cu(UO2)2(AsO4,PO4)2
* 11H2O. Therefore Frondel concluded that uranospathite
is a copper uranyl arsenate-phosphate related to the torbernite group but more highly hydrated than other members of this group.
Hallimond (1954), however, raised objections to
this conclusion. He pointed out that the yellow color of
uranospathite argues against a high copper content. His
objections were supported by the discovery of an urano­s­pathite-like mineral in France (La Crouzille and Sagnes,
Haute-Vienne) which has the same low refractive indices
as Hallimond’s original material (Chervet & Branche
1955). It contains U and P, but no Cu and As. The exact composition, however, was not determined for lack of
material. In addition, Guillemin (cited by Frondel 1954
and by Chervet & Branche 1955) tested a type specimen
of uranospathite furnished by Hallimond and found no
copper.
However, it still took some time until the presence
of aluminum was ascertained as major cation besides
P and U (Walenta 1978). This investigation was based on
uranospathite from Redruth, Cornwall, provided by Hallimond, whose former objections were thus proved to be
correct. There can be no doubt that Frondel investigated
an impure sample.
An electron microprobe analysis of (partially dehydrated) uranospathite gave an Al2O3 content of 2.6 wt.%
(Walenta 1978). In accordance with the new results, the
formula (HAl))0.5(UO2)2(PO4)2 * 20H2O was derived for
uranospathite, taking also into account the water content
determined by an indirect method. This is in close relation to the formula of sabugalite (HAl)0.5(UO2)2(PO4)2 *
8H2O which was considered to be partially dehydrated
uranospathite. A tetragonal cell was derived from the indexed powder data of uranospathite. However, because
the optical properties conform to orthorhombic symmetry,
it was stated that this may only be considered a pseudocell (Walenta 1978).
An aluminum uranyl phosphate was synthesized first
by Magin et al. (1959) and later by Walenta (1978), but
the fully hydrated phase, uranospathite sensu strictu,
was not obtained. The synthetic compound has the formula (HAl)0.5(UO2)2(PO4)2 * 16 H2O, being intermediate between uranospathite with 20 and sabugalite with 8
H2O. Dehydration of this compound led to a composition
very close to that of sabugalite with 8 H2O.
Though the presence of aluminum in uranospathite
and the derived formula was firmly established, this did
not yet mean the end of the matter. Locock et al. (2005)
studied the structure of uranospathite and found that the
mineral additionally contains F as proved by WDS microprobe techniques. Based on a structure refinement,
they derived the empirical formula Al0.86□0.14[(UO2)
(PO4)]2(H2O)20.42F0.58, generalized Al1-x□x [(UO2)(PO4)]2
(H2O)20 + 3x F1-3x, 0 < x < 0.33, which has become the accepted formula by now. As to the structure, Locock et al.
(2005) obtained an orthorhombic cell with a 30.020, b
7.0084, c 7.049 Å, and space group Pnn2. However, the investigated sample from Vernachat, Haute Vienne, France,
was only qualitatively chemically analyzed, not quantitatively. For this reason, Locock et al. considered their formula to be hypothetical, the more so, because it is based
on the assumption of varying Al and F contents and no
anion vacancies. Uranospathite from Redruth, Cornwall,
was included in the study of Locock et al., but also not
quantitatively analyzed. The presence of F, however, was
also analytically confirmed. As to the role of F, it was assumed that it substitutes for part of the H2O coordinating
Al in the structure of the orthorhombic mineral. Locock
et al. also synthesized a triclinic aluminum uranyl phosphate with the formula Al0.67□0.33[UO2)(PO4)]2(H2O)15.5,
but as in former experimental studies, no compound with
the high water content of uranospathite was obtained. The
task remained to determine the formula of uranospathite
by a quantitative chemical analysis of the mineral from
the type locality in Cornwall.
Hurtig (2007) studied uranospathite from Menzenschwand, Black Forest, Germany. Based on the formula
derived by Locock et al., Hurtig communicates the mean
of 13 microprobe measurements on three samples as Al1.2
[(UO2)2(OH)1.6(PO4)1.46(AsO4)0.54] * 6.4 H2O, which corresponds to strongly dehydrated samples. F was not measured. Instead, (OH) was introduced to obtain charge balance. Remarkable is the high content of Al. It is further
of interest that he mentions the presence of iron in very
variable amounts of up to 1.82 wt.% Fe2O3 (~0.2 mole Fe
per formula unit). In addition, the analyzed sample contains 0.39 wt.% CaO.
An arsenate analogue of uranospathite, arsenuranospathite, was described as a new mineral from Menzenschwand
and Wittichen in the Black Forest, Germany, by Walenta
(1978). In this paper, the formula (HAl)0.5(UO2)2(AsO4)2 *
20 H2O was adapted to that of uranospathite. No complete
quantitative analysis was performed for lack of material,
but an Al2O3 content of 2.8 wt.% was measured by electron microprobe on a partially dehydrated sample. A tetragonal cell was derived from the powder data. However,
it was regarded only as a pseudo cell, whereas the true cell
was suggested to be orthorhombic. Walenta (1978) also
attempted to synthesize arsenuranospathite. As in the case
of uranospathite, the fully hydrated mineral with 20 H2O
was not obtained, but only a phase with 16 H2O per for-
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The chemical composition of uranospathite, arsenuranospathite, and associated minerals revisited
mula unit. Locock et al. (2005) verified the presence of
F in arsenuranospathite from Menzenschwand by qualitative WDS microprobe techniques.
Hurtig (2007) also analyzed arsenuranospathite from
Menzenschwand but, as in case of its phosphate analogue from that locality, he did not measure F. Hurtig
(2007) presented the formula Al1.2[(UO2)2(OH)2.2(AsO4)1.6
(PO4)0.2] * 6 H2O as mean of 60 measurements on 13 samples. Noteworthy is again the content of Al and, in addition, the deficit of (AsO4+PO4) with respect to (UO2).
Hurtig compensates this by (OH) groups. As to other constituents, it is mentioned that Fe2O3, though not present in
most samples, could reach 1.03 wt.%.
A detailed analytical study of arsenuranospathite from
Menzenschwand was performed by Chukanov et al.
(2009). They investigated about 50 specimens with arsenuranospathite, collected in the seventies and eighties
of the 20th century, with EDS techniques. In part the specimens were fully hydrated, in part partially dehydrated.
The chemical composition of a fully hydrated specimen
analyzed by Chukanov et al. (2009) is shown in Table
2. It contains a relatively high amount of phosphorus.
They also analyzed a partially dehydrated arsenuranospathite (called analogue of arsenuranospathite) and derived
the empirical formula Al0.98(UO2)2.04[(AsO4)1.66(PO4)0.34]
F0.88(OH)0.14 * 8.77 H2O. Further they present the formula of a PO4-dominant phase, called sabugalite-uranospathite: Al1.01(UO2)2.02[(PO4)1.67(AsO4)0.33]F0.69(OH)0.38 *
nH2O. Regarding the composition, it is further mentioned
in the study that no other elements besides Al, U, P, As
and F (besides O and H) were found above their detection limits. In conclusion, Chukanov et al. (2009) suggest applying the simplified formula Al(UO2)2(AsO4)2F *
20 H2O with 1 F and 20 H2O for arsenuranospathite which
is now accepted by the IMA as the valid one. It is superseding the old formula of Back & Mandarino (2008) derived in analogy to the formula of Locock et al. (2005) for
uranospathite. However, Chukanov et al. (2009) state that
the samples show wide variations of fluorine contents.
In most cases > 0.5 F atoms per formula unit, but several
samples contain < 0.5 F (cf. Fig. 6). This variation, however, is not reflected in the suggested formula. It should
be mentioned that the same formula as ideally attributed
to arsenuranospathite also belongs to the mineral chistyakovaite, excepting the water content. This mineral, however, is structurally not related to arsenuranospathite but
to threadgoldite (Chukanov et al. 2006), that in contrast to
arsenouranospathite contains Al in dimers of edge-sharing octahedra but not in isolated octahedra.
The object of the present study is to obtain more complete chemical analyses of the type specimens of uranospathite from Redruth, Cornwall, and of arsenuranospa-
61
thite from Menzenschwand and Wittichen in the Black
Forest, which hitherto have only been partially analyzed.
In addition, sabugalite, which according to the available analyses does not contain F, is included in the study.
Little data are also available on the role of F in similar
minerals of the autunite group with the general formula
A(UO2)2[(P,As)O4]2 * nH2O. Therefore, minerals such
as metauranocircite, metazeunerite, metaheinrichite, and
bassetite were also analyzed, particularly with respect to
their fluorine content. These minerals analyzed in this
study are mostly intimately associated with the F-bearing
minerals uranospathite or arsenuranospathite.
Sample description
Sample No. L. 1941, Cornwall, England: The second
author owned a sample from the type locality of uranos­
pathite in Cornwall provided by E.A. Jobbins, Geological Survey and Museum, London (part of specimen No.
L.1941, originally belonging to the Ludlam Collection).
This sample had served for the description by Walenta
(1978) and may be considered as type specimen. It was
used in the present study for quantitative analysis by electron microprobe. In the sample, uranospathite is associated and in part intergrown with bassetite. This is also
mentioned by Hallimond (1915) who describes an intergrowth of the two minerals. The crystals of bassetite and
uranospathite look very much alike, though they differ
slightly in color and transparency (Walenta 1978). However, under the microscope they can be easily recognized
optically by their different indices of refraction.
Sample No. SO1,34ab, Sophia mine in Wittichen,
Black Forest, Germany: This type specimen contains
arsenuranospathite occurring in tabular rectangular and
lathlike crystals of less than 0.1 mm in size, incrusting altered uraninite. It is associated with uranospathite, metauranospinite, metakahlerite, metakirchheimerite and
erythrite.
Sample No. MK3,3 a and W1, Menzenschwand,
Black Forest, Germany: The attempt to analyse the type
specimen of arsenuranospathite (Walenta 1978) from
Menzenschwand, the second known type locality in the
Black Forest, was unfortunately not successful. For the
original description as a new species, much of the available scanty material had been used and hence not sufficient material suitable for the analysis was at our disposal.
For the analyses of arsenuranospatite we therefore used
another sample from Menzenschwand which contains the
mineral intimately intergrown with metazeunerite, metaautunite, metauranocircite, chernikovite, uranophane, and
erythrite.
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T. Theye et al.
Sample No. HMM#102193 from Sabugal, and No.
HMM#102197 from Kariz, Portugal: The authors are
indebted to the Harvard Mineralogical and Geological
Museum for providing samples of sabugalite from the
Mina da Quarta Feira, Guarda district, Sabugal County (HMM#102193) and Kariz in the Minho province
(HMM#102197) which belong to the three known type localities of this mineral in Portugal. The material consists
of small-sized tabular crystals and aggregates of yellow
color. In order to check the identity of the samples, the
refractive indices were determined: nZ = 1.583(2) for the
mineral from the Mina da Quarta Feira and nZ = 1.582(2)
for the mineral from Kariz, being rather similar to the
published data (1.584 for the first and 1.583 for the latter
according to Frondel 1951).
with the electron beam. For the WDS analyses, a beam
current as low as 1 nA and a beam size of up to 15 µm
was necessary to prevent substantial loss of crystal water
and resulting too high anhydrous totals. Multiple analyses
on one and the same spot indicate some water loss but
relatively constant rations between cations and F. Further
details on the analyzed elements are summarized in Table
1, with quoted uncertainties based on counting statistics.
The calculated relative precision amounts to 5 % for F,
4 % for Al, 3 % for U, 5 % for P (uranospathite), and 3 %
for As (arsenuranospathite). Because of loss of water,
the quoted statistical uncertainty should be considered
as minimum value. In addition, test measurements with
the ED system of the EMP have been performed on areas
up to 30 × 30 µm in size, applying a low beam current of
1 nA. Calculated cation to F ratios show the same range
as in case of WDS analyses. Structural formulae of the
analyzed autunite group minerals (Table 2 and 3) have
been calculated on the base of (P+As) = 2 per formula
unit (pfu).
Element distribution images of uranospathite are produced by stepwise movement of the sample under the
electron beam. Experimental conditions have been 15 kV,
20 nA, 200 ms counting time per step.
Methods
The chemical compositions were determined with a
CAMECA SX100 electron microprobe analyzer in WDS
mode, with 15 kV acceleration voltage on polished thin
sections of rock fragments. The applied standards are
natural and synthetic components: uraninite (U; tested
against synthetic metallic uranium), graftonite (P; provided by F. Hatert, Liège, Belgium), hematite (Fe), GaAs
(As), chalcopyrite (Cu), wollastonite (Ca, Si), BaF2 (F),
barite (Ba), Al2O3 (Al), CoO (Co). Oxygen was not analyzed but calculated by stoichiometry. Fluorine has been
measured in differential PHA mode. Under these conditions, the influence of spectral interference of F Kα with
1st order of Fe Lα, 2nd order of As Lβ, and 3rd order
of P Kα is negligible. Determined interference factors are
much below the analytical uncertainty quoted in Table 1.
As already described by Locock et al. (2005), uranospathite is very sensible for beam damage during analyses
Uranospathite from Redruth in Cornwall
As mentioned above, a complete analysis of a type specimen from the locality in Redruth, Cornwall, was not
available until now. Locock et al. (2005) only state that
the presence of fluorine was confirmed by WDS microprobe methods in a sample from the type locality (his
sample no. 17-F). In contrast, the presented chemical data
are derived from a structure refinement of a sample from
the Venachat mine in Haute Vienne, France.
Table 1. Experimental conditions for electron microprobe analyses. Uncertainties and detection limits refer to applied condition of 15 kV,
1 nA, and peak counting time equals background counting time.
analytical line
F Kα
Mg Kα
Al Kα
P Kα
Ca Kα
Fe Kα
Co Kα
Cu Kα
As Lα
Ba Lα
U Mβ
diffraction
crystal
PC1
TAP
TAP
LPET
PET
LLIF
LLIF
LLIF
TAP
LPET
PET
standard
BaF2
periclase
corundum
graftonite
wollastonite
hematite
CoO
chalcopyrite
GaAs
baryte
uraninite
peak counting
time (s)
60
20
20
20
20
20
20
20
20
20
20
detection limit
(wt.%)
0.09
0.13
0.11
0.32
0.10
0.31
0.63
0.62
0.68
0.26
1.2
typical uncertainty 1 σ of elements
for uranospathite (wt.%)
0.06
0.11
0.37
1.76
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The chemical composition of uranospathite, arsenuranospathite, and associated minerals revisited
63
Table 2. Representative electron microprobe analyses of uranospathite (US) and arsenuranospathite (AUS) from Redruth (Cornwall, England), Menzenschwand and Wittichen (both Black Forest, Germany). * = calculated; BLD = below detection limit.
Mineral
Location
US
Cornwall
US
Cornwall
US
Cornwall
US
Cornwall
AUS
Wittichen
AUS
Wittichen
AUS
Wittichen
12
AUS
Menzenschwand
8
AUS
Menzenschwand
14
No.
2
3
4
8
10
11
MgO
Al2O3
P2O5
CaO
FeO
CoO
CuO
As2O5
BaO
UO3
F
Total
BDL
5.72
15.84
BDL
BDL
BDL
BDL
BDL
BDL
64.70
1.22
87.48
BDL
5.68
15.72
BDL
BDL
BDL
BDL
BDL
BDL
66.60
0.96
88.96
BDL
5.71
16.04
BDL
BDL
BDL
BDL
BDL
BDL
66.80
0.75
89.30
BDL
5.35
15.78
0.00
BDL
BDL
BDL
BDL
BDL
66.70
1.65
89.48
BDL
4.38
0.18
0.23
BDL
0.75
BDL
23.64
BDL
58.30
0.36
87.84
BDL
4.51
BDL
BDL
BDL
BDL
BDL
23.48
BDL
56.90
0.76
85.65
BDL
5.08
BDL
BDL
BDL
BDL
0.46
24.26
BDL
55.8
1.38
86.98
BDL
4.27
0.99
0.41
0.31
BDL
BDL
21.40
BDL
58.6
1.30
87.28
BDL
3.70
0.37
BDL
BDL
BDL
BDL
20.21
BDL
55.1
1.71
81.09
49.02
1.59
72.71
U
P
As
2.03
2.00
0.00
2.10
2.00
0.00
2.04
2.00
0.00
2.09
2.00
0.00
1.96
0.02
1.98
1.94
0.00
2.00
1.85
0.00
2.00
2.05
0.14
1.86
2.13
0.06
1.94
2.00
0.48
1.52
Al
1.01
1.01
0.98
0.94
0.83
0.86
0.94
0.84
0.80
0.97
Mg
Fe
Co
Cu
Ba
Ca
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.10
0.00
0.00
0.04
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.05
0.00
0.00
0.00
0.04
0.00
0.00
0.00
0.07
0.00
0.00
0.00
0.00
0.00
0.00
OH*
F
0.57
0.57
0.67
0.46
0.71
0.34
0.16
0.78
0.57
0.18
0.36
0.39
0.46
0.69
0.09
0.68
0.00
0.99
AUS
Menzenschwand
Chukanov
et al. 2009
4.23
2.90
14.97
0.98
Fig. 1. Backscattered electron image of uranospathite from Redruth, Cornwall. The F
content per formula unit is given as numerical
values beside the analytical spots. The box indicates the location of the area shown in Fig. 2.
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In backscattered electron images, uranospathite from
Cornwall appears to be slightly heterogeneous (Fig. 1)
which may be due to variable water contents. The molar
proportions of major elements except fluorine, however,
are relatively consistent (Table 2). The mean value of U is
2.02 pfu, and that of Al 0.97 pfu (pfu = per formula unit).
The compositional range of Al is between 0.86 and 1.03
Al pfu. Accordingly, the analyzed crystals are essentially
pure Al-uranyl phosphate, with bivalent cations below
detection limit. The water content was not measured. If
the H2O content is calculated by difference to 100 wt.%,
3 to 11 H2O pfu result pointing to a significant degree of
dehydration. It is not clear whether the low water contents
result from post-crystallization alteration processes or decomposition under the electron beam in the vacuum of the
microprobe.
Fluorine is present in all analyzed crystals. The calculated formula contents vary between 0.3 and 1.0 F. As can
be derived from the element distribution image (Fig. 2),
the distribution of F content is heterogeneous, even within
single crystals. It appears that low F content particular occur in the rim and along cleavage planes, pointing to a
post-crystallization (superficial?) alteration process. In
addition, it should be mentioned that the F distribution
image well correlates with the results of the spot analyses
given in Fig. 1.
The formula of Locock et al. (2005), Al1-x□x[(UO2)
(PO4)]2(H2O)20 + 3x F1-3x, 0 < x < 0.33, though not based on
analytical data of type material, is accepted as the valid
uranospathite formula by the IMA at present. This formula is based on coupled charge balance involving F and
Al. However, our analyses do not conform to this ideal
formula but indicate that, on a formula unit base, relatively consistent values of 0.97 for Al are combined with
strongly varying F contents between 0.3 and 1.0 pfu. To
account for charge balance in uranospathite with a low F
content as analyzed here, it is proposed to consider the
incorporation of (OH), as discussed below.
physical intergrowth of the respective endmembers arsenuranspathite, zeunerite, metakahlerite, metakirchheimerite, and metaheinrichite. Only Al-rich analyses with Al
> 0.7 pfu and M2+< 0.2 are considered to represent arsenuranospathite without significant contamination. (Table 2)
After normalizing (P+As) to 2 pfu, U is close to 2.0
pfu. The average Al content is 0.8 pfu; the relatively large
variation of the Al content (Fig. 3) may be due to physical
intergrowths with other autunite group minerals. As with
uranospathite, the chemical analyses of arsenuranospathite from Wittichen indicate that the mineral is also not
in the fully hydrated state with 20 H2O pfu.
The F content is variable, ranging 0.2 to 0.7 F pfu (Table 2, Fig. 3). As in uranospathite from Cornwall, strong
variation even occurs in intimately associated crystals
(analyses 10, 11, 12 in Table 2 are just a few µm apart from
each other). The majority of the analyses has a relatively
low F content of less than 0.5 pfu. For example, analysis
#10 in Table 2 contains 0.36 wt.% F, corresponding to 0.18
pfu. It is evident, that such a small F content makes it
doubtful to include F instead of OH in the formula of arsenuranospathite as proposed by Chukanov et al. (2009).
Also in this case, charge balance can only be achieved
with (OH) in addition to F
b. Menzenschwand: At Menzenschwand, arsenuranospathite is not pure aluminum uranyl arsenates but
may contain small amounts of phosphorus (0.6 wt.% on
average). Some crystals also contain a small amount of
divalent cations, in particular Ca. The average Al content
of 0.87 pfu is higher than in the Wittichen arsenuranospathite, and the variation of the Al contents (0.79 to 0.94 pfu;
Fig. 3) is relatively small. The fluorine content is always
relatively high, amounting to 0.90 atoms pfu on average,
but the variation ranging from 0.6 to 1.0 is also significant
(Fig. 3). These values are in the range of values reported
by Chukanov et al. (2009) for arsenuranospathite from
Menzenschwand.
In summary, it can be stated that the F content in arsenuranospthatite in both localities is variable: at Menzenschwand, the values are close to 0.9, whereas at the
other type locality, Wittichen, the contents are significantly lower and vary from 0.2 to 0.7 F atoms pfu with 0.37 as
mean value (Fig. 3). In contrast, Al shows less variation in
both occurrences.
Arsenuranospathite
Two type localities of arsenuranospathite exist: Wittichen
in the Central Black Forest (Sophia Mine) and Menzenschwand in the Southern Black Forest (Walenta 1978).
a. Wittichen: In addition to the major elements in arsenuranospathite (U, As, Al, O), some analyses of arsen­
uranospathite from Wittichen contain small quantities of
the divalent elements Ca, Ba, Fe, Cu and Co. Variation of
divalent elements occurs on a micrometer scale. The presence of these minor elements in arsenuranospathite may
be due to true solid solutions with unknown extend and/or
Sabugalite
The chemical composition of sabugalite with the IMAapproved formula HAl(UO2)4(PO4)4*16 H2O is closely
related to uranospathite. The purpose of our study was to
analyze the composition of sabugalite with respect to the
presence of F.
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Fig. 2. Element distribution images of Al and F of the
area indicated in Fig. 1, uranospathite from Redruth,
Cornwall. The crystals are relatively homogeneous
with respect to Al, but with a heterogeneous F distribution (low content: blue; high content: red). The F
contents qualitatively well correlate with the F analyses
given in Fig. 1. Images are 333 µm across.
(range 0.9 –1.2), whereas in Sabugal only 0.7 Al pfu (range
0.7– 0.8) are present. In addition, the mineral from Kariz
contains some As (average value of 0.15 pfu) substituting
for P, in agreement with the composition given by Frondel. In contrast to the water-rich Al-bearing members of
the autunite group, uranospathite and arsenuranospathite,
sabugalite from both localities does not contain F in detectable amounts.
Fluorine content of autunite group
minerals associated with uranospathite and
arsenuranospathite
On the Menzenschwand sample, arsenuranospathite is associated with chernikovite, metaheinrichite, metazeune­
rite, metauranocircite, and meta-autunite. Metauranospinite in addition to arsenuranospathite occur on the Wittichen
sample. A common feature of these associated minerals is
that Fe, Mg, Cu, Co, Ba, and Ca are present in variable
proportions, indicating an intimate intergrowth or a miscibility of the respective minerals. Aluminum is mostly
below detection limit, and fluorine is present in very low
amounts only (mostly < 0.1, rarely up to 0.3 wt.%). Some
F and Al-richer compositions are probably due to a close
intergrowth with arsenuranospathite. At Redruth, uranospathite is closely associated with bassetite. In contrast to
the associated uranospathite, bassetite only contains little
F, mostly in the range of 0.1 pfu. Al in bassetite is below
the detection limit.
In summary, the analyzed autunite group minerals
do not contain significant amounts of fluorine, although
they are spatially directly associated with the F-bearing
arsenuranospathite. This suggests that a crystal-chemical
Fig. 3. A diagram of Al vs. F pfu (pfu = per formula unit) shows a
strong variation of F content in uranospathite and arsenuranospathite from Cornwall, Menzenschwand and Wittichen. Only analyses with Al > 0.7 pfu are shown. Symbols: circle – uranospathite
Cornwall; triangle – arsenuranospathite Wittichen; square – arsenuranospathite Menzschwand.
We analyzed two samples of sabugalite, from the
Mina da Quarta Feira, Guarda district, Sabugal County
and from Kariz in the Minho province. Representative
analyses are given in Table 3. The results are compatible
with the analysis published by Frondel (1951). Sabugalite
from the Kariz locality contains 1.0 Al pfu on the average
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T. Theye et al.
Formulae of uranospathite and
arsenuranospathite
and not a fluid-compositional effect is responsible for the
incorporation of F into the Al-bearing members of the autunite group.
The presence of F as well as the Al content warrants a reconsideration of the original formula of uranospathite and
of arsenuranospathite as derived by Walenta (1978). The
amount of aluminum is definitely higher than given in the
original formula with (HAl)0.5 per (UO2)2. Already the result of the first analysis of arsenuranospathite (Walenta
1978), which gave ~2.80 wt.% Al2O3, points to an amount
of Al higher than originally proposed. Locock et al.
(2005) suggested variable Al contents of 1.00 to 0.66 pfu
in uranospthatite as due to a coupled substitution involving F. Almost ideal Al and F contents of 1.0 and 0.98 pfu,
respectively, are analyzed by Chukanov et al. (2009) for
arsenuranospathite from a sample from Menzenschwand.
The new analyses show that both in uranospathite and
arsenuranospthatite a relative constant Al content of 0.8 to
1.0 pfu is combined with a strong variation of F contents
(Fig. 3). It therefore requires reconsideration whether it
is justified, by modification of the original formula of
Walenta (1978), to include F in the idealized formula as
postulated by Chukanov et al. (2009) Al(UO2)2(AsO4)2F
* 20 H2O. In particular, these authors (according to their
Fig. 3) also obtained a wide range of F contents, ranging
between 0.3 and 1.1 F pfu for uranospthatite/arsenuranospathite (Fig. 4). This fact, in addition to the analyses of
this study, is not compatible with their ideal formula. Locock et al. (2007) derived a generalised formula for uranospathite involving a coupled substitution of Al and F:
Al1-x□x [(UO2)(PO4)]2(H2O)20 + 3x F1-3x, 0 < x < 0.33. This
formula is also not in accordance with the new analyses
Table 3. Representative electron microprobe analyses of sabugalite. BLD = below detection limit.
Mineral
Sabugalite
Sabugalite
Location
Kariz
Sabugal
No.
7
8
MgO
Al2O3
P2O5
CaO
FeO
CoO
CuO
As2O5
BaO
UO3
F
Total
0.91
5.03
13.36
0.17
BDL
BDL
BDL
2.66
BDL
65.0
BDL
87.13
0.13
3.93
16.19
BDL
BDL
BDL
BDL
BDL
BDL
67.5
BDL
87.75
U
P
As
2.15
1.78
0.22
2.07
2.00
0.00
Al
0.93
0.68
Mg
Fe
Co
Cu
Ba
Ca
0.21
0.00
0.00
0.00
0.00
0.03
0.03
0.00
0.00
0.00
0.00
0.00
Fig. 4. Diagram of As/(As+P) vs. F/(F+OH) (molar
proportions) for uranospathite and arsenuranospathite
analyzed in the present work. Only analyses with Al
> 0.7 are shown. For symbols, see Fig. 3. Grey shaded
area is the compositional range analyzed by Chukanov
et al. (2009) as inferred from their Fig. 3.
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Significance of F in minerals of the autunite
group
(c.f. Fig. 3) which indicate that F and Al contents are not
related.
An additional consideration concerns the (OH) content which is necessary to obtain charge balance. Because
of the relatively large analytical uncertainty particularly
for U, we calculated (OH) based on an ideal formula content with U = 2 and (P+As) = 2 pfu. The (OH) content
can then be calculated as (OH) = (OCat –1) * 2 – F, with
OCat being ideal oxygen linked to Al, Mg, Ca, Fe, Co, Cu,
and Ba. The resulting (OH) is variable as the F contents
are (Table 2). Calculated totals of (OH)+F contents vary
around 1 which is a direct consequence of the Al content
being close to 1. The relatively large analytical uncertainly, however, prevents a good precision of this calculation.
Concerning the general formula of fully hydrated uranospathite, the observed independent variation of Al and
F requires, with respect to the formula given by Locock et
al. (2005), the consideration of an independent variation
of F/[F+(OH)]. Respective F and (OH) endmembers are
(x = 0 to 0.33):
The presence of significant amounts of F seems to be
restricted to aluminum-bearing members of the autunite
group with high water content (uranospathite and arsenuranospathite). Sabugalite, an aluminum-bearing member with low water content, does not contain significant
F. Other members of this mineral group also do not contain significant F, even if associated with uranospathite or
arsenuranospathite.
We can only speculate on the reason for this peculiar behaviour of fluorine. It does not seems to be an effect of F-rich and F-poor fluids from which the minerals
formed, because in this case, coexisting minerals should
show similar F contents. It is therefore suggested that the
ability to incorporate F is related to crystal chemical and/
or structural properties of the minerals. In particular, the
strength of hydrogen bonding in the vicinity of Al octahedra may play a role (Hawthorne 2002).
Al1-x□x(UO2)2(PO4)2(H2O)20 + 3x F1-3x (Locock et al. 2005)
Al1-x□x(UO2)2(PO4)2(H2O)20 + 3x(OH)1-3x
Acknowledgements
Uranospathite from Cornwall, accordingly, has x = 0
to 0.1, and F/[F+(OH)] of 0.3 to 1.0.
The same reasoning can be applied for arsenuranospathite
We thank the reviewers, A. Locock and an anonymous, as
well as Associate Editor A. Beran for their helpful comments on the manuscript. We are also grateful to the Mineralogical and Geological Museum of Harvard University
for the loan of specimens of sabugalite.
Al1-x□x(UO2)2(AsO4)2(H2O)20 + 3x F1-3x
Al1-x□x(UO2)2(AsO4)2(H2O)20 + 3x(OH)1-3x
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Manuscript received: March 13, 2014; accepted: August 31, 2015.
Responsible editor: A. Beran
Authors’ addresses:
Thomas Theye (corresp. author), Kurt Walenta, Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Azenbergstr. 18, 70174
Stuttgart, Germany. e-mail: [email protected]
Gregor Markl, Fachbereich Geowissenschaften, Universität Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany.
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