Ammoniomathesiusite, a new uranyl sulfate-vanadate mineral from the Burro mine, San Miguel County, Colorado, USA

Abstract

The new mineral ammoniomathesiusite (IMA 2017-077),
(NH4)5(UO2)4(SO4)4(VO5)·4H2O, was found in the Burro mine, San Miguel County, Utah, USA, where it occurs as a secondary phase on asphaltum/quartz matrix in association with ammoniozippeite (2017-073), gypsum, jarosite and natrozippeite. The mineral forms pale
yellow to greenish-yellow prisms, up to about 0.3 mm long, with pale yellow streak and bright yellow-green fluorescence. Crystals are transparent and have vitreous luster. The mineral is brittle, with Mohs hardness of 2½, stepped fracture and two cleavages: excellent on {110} and good on {001}. The calculated density is 3.672 g/cm3. Ammoniomathesiusite is optically uniaxial (–) with ω = 1.653(2) and ε = 1.609(2) (white light). Pleochroism is O green yellow, E colourless; O > E. Electron microprobe analyses yielded the empirical formula [(NH4)4.75(U1.00O2)4(S1.00O4)4(V1.00O5)·4(H2.07O). The five strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 10.57(46)(110), 7.10(62)(001), 6.41(100)(101), 3.340(35)(240) and
3.226(44)(141). Ammoniomathesiusite is tetragonal, P4/n, a = 14.9405(9), c = 7.1020(5) Å, V = 1585.3(2) Å3 and Z = 2. The structure of ammoniomathesiusite (R1 = 0.0218 for 3427 I >2sigmaI) contains heteropolyhedral sheets based on [(UO2)4(SO4)4(VO5)]5– clusters. The structure is identical to that of mathesiusite, with NH4+
in place of K+.

Full text

Article
Ammoniomathesiusite, a new uranyl sulfate–vanadate mineral from
the Burro mine, San Miguel County, Colorado, USA
Anthony R. Kampf1, Jakub Plášil2, Barbara P. Nash3and Joe Marty4
1
Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA;
2
Institute of Physics ASCR,
v.v.i., Na Slovance 1999/2, 18221 Prague 8, Czech Republic;
3
Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA; and
4
5199 East Silver Oak Road, Salt Lake City, UT 84108, USA
Abstract
The new mineral ammoniomathesiusite (NH
4
)
5
(UO
2
)
4
(SO
4
)
4
(VO
5
)·4H
2
O, was found in the Burro mine, San Miguel County, Utah,
USA, where it occurs as a secondary phase on asphaltum/quartz matrix in association with ammoniozippeite, gypsum, jarosite and
natrozippeite. The mineral forms pale yellow to greenish-yellow prisms, up to ∼0.3 mm long, with pale-yellow streak and bright
yellow–green fluorescence. Crystals are transparent and have vitreous lustre. The mineral is brittle, with Mohs hardness of 2½, stepped
fracture and two cleavages: excellent on {110} and good on {001}. The calculated density is 3.672 g/cm
3
. Ammoniomathesiusite is optic-
ally uniaxial (–) with ω= 1.653(2) and ϵ= 1.609(2) (white light). Pleochroism is: O= green-yellow, E= colourless; O>E. Electron micro-
probe analyses yielded the empirical formula [(NH
4
)
4.75
(UO
2
)
4
(SO
4
)
4
(VO
5
)·4(H
2.07
O). The five strongest powder X-ray diffraction lines
are [d
obs
Å(I)(hkl)]: 10.57(46)(110), 7.10(62)(001), 6.41(100)(101), 3.340(35)(240) and 3.226(44)(141). Ammoniomathesiusite is tetrag-
onal, P4/nwith a= 14.9405(9), c= 7.1020(5) Å, V= 1585.3(2) Å
3
and Z= 2. The structure of ammoniomathesiusite (R
1
= 0.0218 for 3427
I>2σI) contains heteropolyhedral sheets based on [(UO
2
)
4
(SO
4
)
4
(VO
5
)]
5–
clusters. The structure is identical to that of mathesiusite,
with NH+
4in place of K
+
.
Keywords: ammoniomathesiusite, new mineral, uranyl sulfate–vanadate, crystal structure, Burro mine, Colorado, USA
(Received 7 January 2018; accepted 26 January 2018)
Introduction
The Uravan Mineral Belt of the Colorado Plateau, which spans
the Colorado–Utah border, has been a rich source of uranium
and vanadium ores. The mines in this belt have also yielded
many new secondary U and V minerals, the first of which was
carnotite, K
2
(UO
2
)
2
(VO
4
)
2
·3H
2
O, described from the Rajah
mine in the northern portion of the belt by Friedel and
Cumenge (1899). Although mining in what is now called the
Slick Rock district in the southern portion of the belt dates to
around 1900, apparently the Burro mine in that district was not
active until the mid-1950s. The first new mineral to be described
from the Burro mine was metamunirite, NaVO
3
(Evans, 1991),
and recently burroite, Ca
2
(NH
4
)
2
(V
10
O
28
)·15H
2
O, was described
(Kampf et al., 2017). Herein, we describe ammoniomathesiusite,
the third new mineral from the Burro mine.
Ammoniomathesiusite is named as the ammonium analogue of
mathesiusite, K
5
(UO
2
)
4
(SO
4
)
4
(VO
5
)·4H
2
O(Plášil et al., 2014), with
NH
+
4
in place of K
+
. The new mineral and name were approved by
the Commission on New Minerals, Nomenclature and Classification
of the International Mineralogical Association (IMA2017-077). The
holotype and three cotypes are deposited in the collections of the
Natural History Museum of Los Angeles County, 900 Exposition
Boulevard, Los Angeles, CA 90007, USA, catalogue numbers
67248 (holotype), 67249, 67250 and 69251.
Occurrence
Ammoniomathesiusite was collected underground at the Burro
mine, Slick Rock district, San Miguel County, Colorado, USA
(38°2’42’’N, 108°53’23’’W). The Burro mine is near the southern
end of the Uravan Mineral Belt, in which uranium and vanadium
minerals occur together in bedded or roll-front deposits in the
sandstone of the Salt Wash member of the Jurassic Morrison
Formation (Carter and Gualtieri, 1965;Shawe,2011). The uranium
and vanadium ore mineralisation was deposited where solutions
rich in U and V encountered pockets of strongly reducing solutions
that had developed around accumulations of carbonaceous plant
material, still in evidence as carbonised plant remains and notable
logs. Mining operations have exposed both unoxidised and oxidised
U and V phases. Under ambient temperatures and generally oxidis-
ing near-surface conditions, water reacts with pyrite and chalco-
pyrite to form aqueous solutions with relatively low pH, which
then react with the earlier-formed montroseite–corvusite assem-
blages, resulting in diverse suites of secondary minerals. The
NH+
4presumably derives from organic matter in the deposit.
Ammoniomathesiusite is rare and occurs on asphaltum/quartz
matrix in association with ammoniozippeite (Kampf et al., 2018),
Author for correspondence: Anthony R. Kampf, Email: akampf@nhm.org
Associate Editor: Juraj Majzlan
© Mineralogical Society of Great Britain and Ireland 2018
Cite this article: Kampf A.R., Plášil, J., Nash B.P. and Marty J. (2019)
Ammoniomathesiusite, a new uranyl sulfate–vanadate mineral from the Burro mine,
San Miguel County, Colorado, USA. Mineralogical Magazine,83, 115–121. https://
doi.org/10.1180/mgm.2018.112
Mineralogical Magazine (2019), 83, 115–121
doi:10.1180/mgm.2018.112
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gypsum, jarosite and natrozippeite. Other secondary minerals
verified by us to occur in the mine include: andersonite, anserme-
tite, barnesite, brochantite, burroite (Kampf et al., 2017), calcio-
delrioite, calcite, chalcomenite, grantsite, gunterite, hewettite,
huemulite, hughesite, hydrocerussite, kokinosite, lasalite, lindgre-
nite, magnesiopascoite, martyite, metamunirite, metarossite,
metaschoepite, munirite, navajoite, orthoserpierite, pascoite, ros-
site, schindlerite, schröckingerite, serpierite, sherwoodite, strelki-
nite, tyuyamunite, uranopilite, volborthite, wernerbaurite,
zippeite and numerous other potentially new minerals, currently
under study.
Physical and optical properties
Ammoniomathesiusite crystals are {110} prisms, up to ∼0.3 mm
long, with square cross-sections and flat {001} terminations,
sometimes modified by {111} pyramids (Fig. 1). Broad prisms
are typically isolated or intergrown in random orientations
(Fig. 2); narrow prisms, often tapering slightly towards their ter-
minations, occur in sprays or bow-tie-like intergrowths (Fig. 3).
No twinning was observed.
Crystals are yellow to greenish yellow and transparent with vit-
reous lustre. The streak is very pale yellow. The mineral fluoresces
bright yellow–green under a 405 nm laser. The Mohs hardness is
2½, based upon scratch tests. Crystals are brittle with stepped frac-
ture and two cleavages: excellent on {110} and good on {001}. At
room temperature, the mineral decomposes in H
2
O. The density
could not be measured because the mineral decomposes in Clerici
solution. The calculated density based on the empirical formula is
3.672 g/cm
3
. Optically, ammoniomathesiusite is uniaxial (–), with
ω= 1.653(2) and ϵ= 1.609(2), measured in white light. The min-
eral is distinctly pleochroic: O= green yellow, Ecolourless; O>E.
Raman spectroscopy
Raman spectroscopy was conducted on a Horiba XploRA PLUS
spectrometer. Pronounced fluorescence was observed using a
532 nm diode laser; consequently, a 785 nm diode laser was uti-
lised. The power density of the laser beam at the sample was
9.6 mW. The spectrum was recorded from 2000 to 100 cm
−1
,
but was featureless between 2000 and 1200 cm
−1
. The spectrum
from 1400 to 100 cm
−1
, is shown in Fig. 4.
The broad band of low intensity at ∼1200 cm
–1
is probably an
overtone or combination band; a band at nearly the same fre-
quency was observed in the spectrum of mathesiusite (Plášil
et al.,2014), however, with an incorrect assignment. Very weak
Raman bands at 1110 cm
–1
and at 1090 cm
–1
and a broader
band at 1057 cm
–1
with a shoulder at 1065 cm
–1
are attributed
to split triply degenerate ν
3
antisymmetric stretching vibrations
of the SO
4
tetrahedron. A sharp, slightly asymmetric two-
component band of medium intensity at 1010 cm
–1
is assigned
to the ν
1
symmetric stretching vibration of the SO
4
tetrahedron.
A sharp band at 977 cm
–1
is attributed to the symmetric ν
1
(V–
O) stretching mode (cf. Plášil et al.,2014;Frostet al., 2005). A
weak two-component overlapping band at 904 and 894 cm
–1
is
attributed to the ν
3
antisymmetric stretching vibration of the
uranyl ion, UO2+
2. A very strong band at 834 cm
–1
is assigned
the ν
1
symmetric U–O stretching vibration of UO2+
2. The inferred
Fig. 1. Crystal drawing of ammoniomathesiusite crystal; clinographic projection.
Fig. 2. Ammoniomathesiusite prisms on asphaltum. The field of view is 0.84 mm
across.
Fig. 3. Sprays of ammoniomathesiusite prisms on asphaltum. The field of view is
0.84 mm across.
116 Anthony R. Kampf et al.
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Fig. 4. Raman spectrum of ammoniomathesiusite
recorded using a 785 nm diode laser.
Table 1. Chemical composition (in wt.%) for ammoniomathesiusite.
Constituent Mean Range S.D. Standard Normalised
(NH
4
)
2
O 7.35 6.38–7.89 0.57 syn. Cr
2
N 7.06
V
2
O
5
5.38 5.02–5.84 0.30 V metal 5.17
UO
3
67.95 67.40–69.04 0.60 syn. UO
2
65.26
SO
3
19.02 19.02–20.07 0.40 baryte 18.27
H
2
O* 4.42 4.25
Total 104.12 100.01
* Based on structure with O= 33; S.D. –standard deviation.
Table 2. Powder X-ray data (din Å) for ammoniomathesiusite. Only calculated
lines with I≥2 are included.
I
obs
d
obs
d
calc
I
calc
hkl
46 10.57 10.5645 53 110
7.4703 3 200
62 7.10 7.1020 60 001
100 6.41 6.4142 100 101
4 5.91 5.8940 5 111
11 5.28 5.2823 14 220
5 5.13 5.1471 4 201
7 4.85 4.8664 6 211
27 4.71 4.7246 33 310
12 4.244 4.2385 12 221
4 4.093 4.0775 2 301
22 3.933 3.9337 25 311
25 3.575 3.5791 27 321
3.5215 4 330
26 3.460 3.4548 25 102
35 3.340 3.3408 38 240
44 3.226 3.2277 50 141
25 3.140 3.1550, 3.1357 11, 15 331, 212
3 3.024 3.0230 28 241
15 2.926 2.9301 18 150
2.8913 3 302
2.7542 2 341
24 2.703 2.7086, 2.6964 14, 16 151, 322
12 2.578 2.5842, 2.5623 11, 10 251, 530
(Continued)
Table 2. (Continued.)
I
obs
d
obs
d
calc
I
calc
hkl
21 2.539 2.5362 22 412
2.3673 2 003
7 2.359 2.3623 8 620
2 2.294 2.2863 3 342
4 2.232 2.2416, 2.2314 3, 2 621, 213
2.2167 2 541
11 2.184 2.1862 13 252
4 2.153 2.1603 6 223
22 2.119 2.1251, 2.1165, 2.1129 14, 8, 6 631, 313, 170
13 2.0687 2.0719, 2.0555 11, 4 460, 323
7 2.0358 2.0440, 2.0252 4, 4 701, 171
9 1.9886 1.9890, 1.9819 7, 6 461, 143
1.9716 2 721
10 1.9666 1.9618 6 730
1.9500 3 452
14 1.9337 1.9315 14 423
15 1.8855 1.8910, 1.8868 4, 14 731, 632
8 1.8530 1.8676, 1.8471 , 1.8414 6, 5,4 800, 561, 153
7 1.8313 1.8293 5 702
12 1.8000 1.8062, 1.8008, 1.7931 7,3,9 801, 253, 181
6 1.7803 1.7755 4 004
2 1.7395 1.7388, 1.7368 2, 3 533, 570
1.6979 2 381
14 1.6846 1.6871, 1.6841, 1.6830 3, 10, 3 571, 562, 224
1.6722 3 623
7 1.6636 1.6620 6 314
12 1.6407 1.6429 14 182
1.6221 2 633
1.5852 2 703
1.5799 2 291
1.5764 2 553
1.5749 3 390
16 1.5698 1.5688, 1.5678, 1.5591 2, 10, 4 382, 244, 463
1.5375 3 391
4 1.5155 1.5185, 1.5105 5, 2 154, 733
1.5038 2 902
1.4879 2 563
4 1.4816 1.4835 4 491
9 1.4609 1.4662, 1.4650, 1.4594 5, 2, 5 803, 1020, 534
Mineralogical Magazine 117
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U–O bond lengths (after Bartlett and Cooney, 1989) for the uranyl
ion of ∼1.78 Å (from ν
1
), 1.79 Å (from ν
3
; 894) and 1.78 Å (from
ν
3
; 904) are in line with those derived from our X-ray structure
study (see below). A very weak band at 764 cm
–1
can be attributed
to the libration mode of the H
2
O or to the stretching V–O
eq
vibra-
tion. A broader band at 688 cm
–1
, along with the weak band at
650 cm
–1
, can be related to V–O
eq
vibrations (cf. Plášil et al.,
2014; Knyazev, 2000; Chernorukov et al., 2000). The two-
component band with maxima at 625 and 615 cm
–1
is attributed
to the ν
4
(δ) triply degenerated antisymmetric stretching vibrations
of the SO
4
tetrahedron. Broad bands at 590 and 550 cm
–1
are
probably related to the V–O
eq
vibrations as well. Raman bands
at 482 and at 459 cm
–1
are related to the split ν
2
(δ) doubly degen-
erate bending vibrations of the SO
4
tetrahedron. A very weak band
at 373 cm
–1
is related to the ν
Rotational
of NH+
4(Heyns et al.,1987).
The split ν
2
(δ)UO
2
2+
doubly degenerate bending vibrations are
represented by the broader component band at 244 cm
–1
. The
rest of the bands are related to the unclassified lattice modes.
Chemical composition
Chemical analyses (seven points on six crystals) were performed
at the University of Utah, USA on a Cameca SX-50 electron
microprobe with four wavelength dispersive spectrometers and
using Probe for EPMA software. Analytical conditions were
15 kV accelerating voltage, 10 nA beam current and a beam diam-
eter of 5 µm. Counting times were 30 s on peak and 30 s on back-
ground for each element. Raw X-ray intensities were corrected for
matrix effects with a φρ(z) algorithm (Pouchou and Pichoir,
1991). Time-dependent intensity corrections were applied to N,
U, V and S. Wave-scans across Mg, Al, Na and K peak positions
showed these elements to be absent.
Because insufficient material is available for a direct determin-
ation of H
2
O, it is calculated based upon the structure determin-
ation. The crystals did not take a good polish and there was
minor beam damage. The loss of weakly held H
2
O under vacuum
and/or during analyses would account for the high electron
microprobe analytical totals when calculated H
2
O is included. The
somewhat lower analysed (NH
4
)
2
O content compared to that indi-
cated by the structure refinement (4.75 vs. 4.92 N atoms per formula
unit) could be due to a small amount of H
3
O
+
in place of NH+
4in
the structure; however, the presence of H
3
O
+
would imply highly
acidic conditions. Considering that H
3
O
+
has not been confirmed
in any other phases in the Burro mine mineral assemblages, it
seems more likely that the somewhat low analysed (NH
4
)
2
Ocontent
Table 3. Data collection and structure refinement details for
ammoniomathesiusite.
Crystal data
Structural formula (NH
4
)
4.92
(UO
2
)
4
(SO
4
)
4
(VO
5
)·4H
2
O
Crystal size (μm) 140 × 70 × 35
Space group P4/n
Unit-cell dimensions (Å) a= 14.9405(9), c= 7.1020(5)
V(Å
3
) 1585.30(18)
Z2
Density (for above formula) ( g cm
–3
) 3.680
Data collection
Diffractometer Rigaku R-Axis Rapid II
X-ray radiation/power MoKα(λ= 0.71075 Å)/50 kV, 40 mA
Temperature (K) 293(2)
Absorption coefficient (mm
–1
) 21.033
F(000) 1562.9
θrange (°) 3.46 to 27.49
Index ranges −19 ≤h≤19, –19 ≤k≤19, –8≤l≤9
Reflections collected/unique 10,871/1815; R
int
= 0.039
Reflections with I>2σI1602
Completeness to θ= 27.49° 99.5%
Refinement
Refinement method Full-matrix least-squares on F
2
Parameter/restraints 130/20
GoF 1.077
Final Rindices [I>2σI]R
1
= 0.0218, wR
2
= 0.0443
Rindices (all data) R
1
= 0.0271, wR
2
= 0.0459
Largest diff. peak/hole (e
–
Å
–3
) +1.38/–0.73
R
int
=Σ|F
o
2
–F
o
2
(mean)|/Σ[F
o
2
]. GoF = S={Σ[w(F
o
2
–F
c
2
)
2
]/(n–p)}
1/2
.R
1
=Σ||F
o
|–|F
c
||/Σ|F
o
|. wR
2
={Σ[w
(F
o
2
–F
c
2
)
2
]/Σ[w(F
o
2
)
2
]}
1/2
;w= 1/[σ
2
(F
o
2
)+(aP)
2
+bP] where ais 0.0147, bis 5.5409 and Pis
[2F
c
2
+Max(F
o
2
,0)]/3.
Table 4. Atom coordinates and displacement parameters (Å
2
) for ammoniomathesiusite.
x/ay/bz/cU
eq
U
11
U
22
U
33
U
23
U
13
U
12
N1 0.1123(3) 0.2997(4) 0.3761(6) 0.0337(11) 0.031(3) 0.046(3) 0.024(2) −0.003(2) 0.000(2) −0.003(2)
H1a 0.078(3) 0.250(2) 0.359(7) 0.050
H1b 0.096(3) 0.337(3) 0.284(6) 0.050
H1c 0.1674(19) 0.282(3) 0.364(7) 0.050
H1d 0.100(3) 0.323(3) 0.485(4) 0.050
N2* 0 0 0 0.051(5) 0.029(5) 0.029(5) 0.094(12) 0 0 0
H2 −0.009(5) 0.0475(11) 0.0726(18) 0.050
U 0.30770(2) 0.06726(2) 0.13503(2) 0.01279(7) 0.01107(10) 0.01043(10) 0.01685(10) −0.00077(6) −0.00005(6) 0.00021(6)
S 0.80289(7) 0.14358(7) 0.12364(16) 0.0150(2) 0.0117(5) 0.0109(5) 0.0225(6) 0.0006(4) 0.0005(4) −0.0010(4)
V 0.5 0 0.3274(2) 0.0107(3) 0.0092(4) 0.0092(4) 0.0136(7) 0 0 0
O1 0.8082(2) 0.0460(2) 0.1593(5) 0.0221(8) 0.0178(17) 0.0122(16) 0.036(2) 0.0038(15) −0.0007(15) −0.0020(14)
O2 0.3411(2) 0.0371(2) −0.0977(5) 0.0222(7) 0.0238(18) 0.0193(17) 0.0235(18) −0.0037(14) 0.0005(15) 0.0016(15)
OW3 0.0000(4) 0.1354(4) 0.3922(8) 0.0621(15) 0.054(3) 0.060(4) 0.072(4) −0.012(3) −0.016(3) 0.006(3)
H3a 0.005(5) 0.093(3) 0.327(7) 0.050
H3b 0.023(5) 0.129(4) 0.491(5) 0.050
O4 0.2696(2) 0.0993(2) 0.3626(4) 0.0219(7) 0.0214(18) 0.0236(18) 0.0207(17) −0.0053(14) 0.0046(14) −0.0028(15)
O5 0.8746(2) 0.1663(2) −0.0104(5) 0.0226(8) 0.0137(16) 0.0153(17) 0.039(2) 0.0040(15) 0.0083(15) 0.0015(14)
O6 0.7157(2) 0.1615(2) 0.0306(5) 0.0186(7) 0.0129(15) 0.0176(17) 0.0254(17) 0.0055(14) 0.0009(14) 0.0010(14)
O7 0.3910(2) −0.0504(2) 0.2496(4) 0.0155(7) 0.0128(15) 0.0116(15) 0.0220(17) −0.0029(13) −0.0013(13) 0.0007(13)
O8 0.8118(3) 0.1925(2) 0.2979(5) 0.0289(8) 0.033(2) 0.025(2) 0.0282(19) −0.0061(16) −0.0057(17) 0.0006(17)
O9 0.5 0 0.5521(10) 0.0304(17) 0.034(3) 0.034(3) 0.023(4) 0 0 0
* N2 site refined occupancy = 0.92(4).
118 Anthony R. Kampf et al.
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is due to loss under vacuum (along with the H
2
O noted above) prior
to analyses. The results are given in Table 1.
The empirical formula (calculated on the basis of 33 O atoms per
formula unit) is [(NH
4
)
4.75
(U
1.00
O
2
)
4
(S
1.00
O
4
)
4
(V
1.00
O
5
)·4(H
2.07
O)
[Excess H is included for charge balance]. The ideal formula is
(NH
4
)
5
(UO
2
)
4
(SO
4
)
4
(VO
5
)·4H
2
O, which requires (NH
4
)
2
O7.41,
V
2
O
5
5.17, UO
3
65.10, SO
3
18.22 and H
2
O 4.10, total 100.00 wt.%.
The Gladstone-Dale compatibility index 1 –(K
P
/K
C
) for the empir-
ical formula is 0.009, in the superior range (Mandarino, 2007), using
k(UO
3
) = 0.118, as provided by Mandarino (1976).
X-ray crystallography and structure refinement
Powder X-ray studies were done using a Rigaku R-Axis Rapid II
curved imaging plate microdiffractometer, with monochromatised
MoKαradiation (λ= 0.71075 Å). A Gandolfi-like motion on the φ
and ωaxes was used to randomise the samples. Observed dvalues
and intensities were derived by profile fitting using JADE 2010
software (Materials Data, Inc.). The powder data presented in
Table 5. Selected bond distances (Å) for ammoniomathesiusite.
U–O4 1.779(3) N1–O4 2.973(6) N2–O5 ( × 4) 3.113(3) S–O8 1.443(4)
U–O2 1.785(3) N1–O8 2.975(6) N2–O1 ( × 4) 3.156(3) S–O5 1.473(3)
U–O7 2.302(3) N1–OW3 2.975(8) N2–OW3 ( × 4) 3.442(6) S–O1 1.483(3)
U–O7 2.355(3) N1–O6 2.989(5) <N2–O> 3.237 S–O6 1.486(3)
U–O6 2.383(3) N1–O2 3.046(6) <S–O> 1.471
U–O1 2.427(3) N1–O8 3.093(6) V–O9 1.596(7)
U–O5 2.449(3) N1–O7 3.128(5) V–O7 ( × 4) 1.876(3) Hydrogen Bonds*
<U–O
Ur
> 1.782 N1–O2 3.216(6) <V–O> 1.820 OW3–O4 3.041(7)
<U–O
eq
> 2.383 N1–O9 3.469(5) OW3–O8 3.013(7)
<N1–O> 3.096
* Note that there are no obvious hydrogen bonds through H3a and there are two apparent hydrogen bonds through H3b.
Table 6. Bond-valence analysis for ammoniomathesiusite. Values are expressed
in valence units.*
U S V N1 N2 H bonds Σ
O1 0.45 1.46 0.08
×4↓
1.99
O2 1.74 0.11, 0.07 1.92
OW3 0.13 0.04
×4↓
−0.12 0.09
O4 1.76 0.13 0.06 1.95
O5 0.43 1.50 0.09
×4↓
2.02
O6 0.49 1.45 0.13 2.07
O7 0.58, 0.52 0.82
×4↓
0.09 2.01
O8 1.61 0.13, 0.10 0.06 1.90
O9 1.69 0.03
×4→
1.81
Σ5.96 6.02 4.97 0.92 0.84
*NH
+
4–O bond valence parameters from Garcia-Rodriguez et al.(2000). U
6+
–O, V
5+
–OandS
6+
–O
bond-valence parameters are from Gagné and Hawthorne (2015). Hydrogen-bond strengths
associated with OW3 are based on O–O bond lengths from Ferraris and Ivaldi (1988).
Table 7. Comparison of ideal formulas, cell parameters, optical properties and
calculated densities (ideal) for ammoniomathesiusite and mathesiusite (Plášil
et al., 2014).
Ammoniomathesiusite Mathesiusite
Ideal formula (NH
4
)
5
(UO
2
)
4
(SO
4
)
4
(VO
5
)·4H
2
OK
5
(UO
2
)
4
(SO
4
)
4
(VO
5
)·4H
2
O
Space group P4/nP4/n
a(Å) 14.9405(9) 14.9704(10)
c(Å) 7.1020(5) 6.8170(5)
V(Å
3
) 1585.30(18) 1527.78(18)
Z22
Optical class Uniaxial (–) Uniaxial (–)
ω1.653(2) 1.634(3)
ϵ1.609(2) 1.597(3)
Pleochroism O= green yellow, E= colourless None observed (colourless)
Density (g cm
–3
) 3.681 4.049
Fig. 5. The structure of ammoniomathesiusite viewed down c. The unit-cell outline is
shown by dashed lines.
Fig. 6. The structure of ammoniomathesiusite viewed down a
2
. The unit-cell outline is
shown by dashed lines.
Mineralogical Magazine 119
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Table 2 show good agreement with the pattern calculated from the
structure determination. Unit-cell parameters refined from the
powder data using JADE 2010 with whole pattern fitting are a=
14.9519(14), c= 7.1083(8) Å and V= 1589.1(3) Å
3
.
The single-crystal structure data were collected at room tem-
perature using the same diffractometer and radiation noted
above. The data were processed using the Rigaku CrystalClear
software package and an empirical (multi-scan) absorption cor-
rection was applied using the ABSCOR program (Higashi, 2001)
in the CrystalClear software suite. The structure was solved by dir-
ect methods using SIR2011 (Burla et al., 2012). SHELXL-2016
(Sheldrick, 2015) was used for the refinement of the structure.
Difference-Fourier syntheses located all non-hydrogen atoms
not located in the original structure solution, and subsequent
cycles located all H sites. The structure was found to be identical
to that of mathesiusite (Plášil et al., 2014) and all atom sites were
transformed to correspond to that structure, with two NH
4
sites
in place of the two K sites in mathesiusite. The H atom sites
associated with OW3 were refined with soft restraints of 0.82(3)
Å on the O–H distances and 1.30(3) Å on the H–H distances,
and those for the H sites associated with N1 and N2, with soft
restraints of 0.90(3) Å on the O–H distances and 1.45(3) Å on
the H–H distances. The U
eq
of each H was set to 0.05. All
non-hydrogen sites refined to full occupancy, except the N2
site, which refined to an occupancy of 0.92(4). Data collection
and refinement details are given in Table 3, atom coordinates
and displacement parameters in Table 4, selected bond distances
in Table 5 and a bond-valence analysis in Table 6. A comparison
of the ideal formulas, cell parameters, optical properties and
calculated densities (ideal) for ammoniomathesiusite and mathe-
siusite is provided in Table 7.
The crystallographic information files have been deposited
with the Principal Editor of Mineralogical Magazine and are avail-
able as Supplementary material (see below).
Description and discussion of the structure
The U site in the structure of ammoniomathesiusite is surrounded
by seven O atoms forming a squat UO
7
pentagonal bipyramid.
This is the most typical coordination for U
6+
, particularly in
uranyl sulfates, where the two short apical bonds of the bipyramid
constitute the UO
2
uranyl group (Burns, 2005). Sulfur is coordi-
nated by four O atoms at the distances typical for tetrahedral
coordination, ∼1.47 Å. Vanadium is in square pyramidal coordin-
ation, bonded strongly to one O atom at the distance of 1.596 Å
(vanadyl bond; cf. Schindler et al.,2000) and four O atoms at
the distances of 1.876 Å. This (4 +1) coordination is one of the
characteristic environments for the V
5+
cation (Schindler et al.,
2000). The N1 atom (NH
4
1 group) is [9]-coordinated with an
average bond length ∼3.10 Å, while the N2 atom (NH
4
2 group)
is [12]-coordinated with an average N–O bond length of
∼3.24 Å (Table 5). Both NH
4
groups are linked to the only
H
2
O molecule (OW3) in the structure.
The structure (Figs 5 and 6) contains heteropolyhedral sheets
based on [(UO
2
)
4
(SO
4
)
4
(VO
5
)]
5–
clusters. These clusters arise
from linkages between corner-sharing quartets of uranyl pen-
tagonal bipyramids, which define a square-shaped void at the cen-
tre of which is the base of the VO
5
square pyramid. Adjacent
corner-shared uranyl pentagonal bipyramids are also linked
through SO
4
tetrahedra, with which they share corners. Each
SO
4
shares a third vertex with a uranyl pentagonal bipyramid
in another cluster to form the sheets. The NH+
4cations are located
between the sheets, together with the H
2
O group. The corrugated
sheets are stacked perpendicular to c. These heteropolyhedral
sheets are similar to those in the structures of synthetic uranyl
chromates (Unruh et al., 2012) and molybdates (Obbade et al.,
2003).
Supplementary material. To view supplementary material for this article,
please visit https://doi.org/10.1180/mgm.2018.112
Acknowledgements. Structures Editor Peter Leverett and an anonymous
reviewer are thanked for their constructive comments on the manuscript. A
portion of this study was funded by the John Jago Trelawney Endowment to
the Mineral Sciences Department of the Natural History Museum of Los
Angeles County. We would like to thank Don Coram, the owner of the
Burro mine, for allowing us access to the property, and to Okie Howell and
Jess Fulbright for providing logistical support during our visits.
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