Mineralogical Magazine (2021), 85, 438–443
doi:10.1180/mgm.2021.33

ArticleUranoclite, a new uranyl chloride mineral from the Blue Lizard mine,
San Juan County, Utah, USA
Anthony R. Kampf1*, Jakub Plášil2, Travis A. Olds3, Barbara P. Nash4 and Joe Marty5

1

Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA; 2Institute of Physics ASCR,
v.v.i., Na Slovance 1999/2, 18221 Prague 8, Czech Republic; 3Section of Minerals and Earth Sciences, Carnegie Museum of Natural History, 4400 Forbes Avenue,
Pittsburgh, Pennsylvania 15213, USA; 4Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA; and 55199 East Silver Oak Road,
Salt Lake City, UT 84108, USA

Abstract
The new mineral uranoclite (IMA2020-074), (UO2)2(OH)2Cl2(H2O)4, was found in the Blue Lizard mine, San Juan County, Utah, USA,
where it occurs as tightly intergrown aggregates of irregular yellow crystals in a secondary assemblage with gypsum. The streak is very
pale yellow and the fluorescence is bright green–white under 405 nm ultraviolet light. Crystals are translucent with vitreous lustre. The
tenacity is brittle, the Mohs hardness is ∼1½, the fracture is irregular. The mineral is soluble in H2O and has a calculated density of
4.038 g⋅cm–3. Electron microprobe analyses provided (UO2)2(OH)2.19Cl1.81(H2O)4. The six strongest powder X-ray diffraction lines
are [dobs Å(I )(hkl)]: 8.85(38)(002), 5.340(100)(200, 110), 5.051(63)(202), 4.421(83)(112, 004, 202), 3.781(38)(212) and 3.586(57)(014, 204). Uranoclite is monoclinic, P21/n, a = 10.763(8), b = 6.156(8), c = 17.798(8) Å, β = 95.656(15)°, V = 1173.5(18) Å3 and Z = 4.
The structure is the same as that of synthetic (UO2)2(OH)2Cl2(H2O)4 in which the structural unit is a dimer consisting of two pentagonal
bipyramids that share an equatorial OH–OH edge. The dimers are linked to one another only by hydrogen bonding. This is the second
known uranyl mineral containing essential Cl and the first in which Cl coordinates to U6+.
Keywords: uranoclite, new mineral, uranyl chloride, crystal structure, Raman spectroscopy, Blue Lizard mine, Red Canyon, Utah, USA(Received 30 January 2020; accepted 26 March 2020; Accepted Manuscript published online: 31 March 2020; Associate Editor: Sergey V
Krivovichev)

Introduction
The Blue Lizard mine in Red Canyon, Utah, is now well known asa prolific source of new minerals and particularly for its many Nauranyl sulfates. Of the 22 new minerals described from this mine,
all are sulfates, 16 are Na uranyl sulfates and three are uranyl sulfates that do not contain essential Na. The new mineral uranoclite,(UO2)2(OH)2Cl2(H2O)4, described herein, is the first new mineraldescribed from the Blue Lizard mine that is not a sulfate. Notably,
it also does not contain essential Na. Uranoclite is only the second
known uranyl mineral containing essential Cl, the first being bluelizardite, Na7(UO2)(SO4)4Cl (Plášil et al., 2014), which was also
first described from the Blue Lizard mine. Interestingly, Cl plays
very different roles in the structures of these two minerals.
Uranoclite is named for its composition. It is the first uranyl
chloride mineral that contains no other anions other thanhydroxyl. The phase has previously been synthesised and its
chemical name is di-μ-hydroxido-bis[diaquachloridodioxidouranium(VI)] (Huys et al., 2010). The new mineral and name wereapproved by the Commission on New Minerals, Nomenclature
and Classification of the International Mineralogical Association(IMA2020-074, Kampf et al., 2021). The description is based on*Author for correspondence: Anthony R. Kampf, Email: akampf@nhm.org
Cite this article: Kampf A.R., Plášil J., Olds T.A., Nash B.P. and Marty J. (2021)
Uranoclite, a new uranyl chloride mineral from the Blue Lizard mine, San JuanCounty, Utah, USA. Mineralogical Magazine 85, 438–443. https://doi.org/10.1180/
mgm.2021.33

two cotype specimens, both micromounts, deposited in the collections of the Natural History Museum of Los Angeles County, 900
Exposition Boulevard, Los Angeles, CA 90007, USA, catalogue
numbers 75101 and 75102.
Occurrence
Uranoclite was found in efflorescent crusts on mine walls underground in the Blue Lizard mine (37°33′ 26′′ N, 110°17′ 44′′ W), Red
Canyon, White Canyon District, San Juan County, Utah, USA.
The mine is ∼72 km west of the town of Blanding, Utah, and∼22 km southeast of Good Hope Bay on Lake Powell. Detailed
historical and geological information on the Blue Lizard mine is
described elsewhere (e.g. Kampf et al., 2015a), and is primarily
derived from a report by Chenoweth (1993). Abundant secondary
uranium mineralisation in Red Canyon is associated with postmining oxidation of asphaltum-rich sandstone beds laced with uraninite and sulfides in the damp underground environment. Uranoclite
is a very rare mineral in the secondary mineral assemblages of theBlue Lizard mine. It occurs with gypsum on matrix comprised
mostly of subhedral to euhedral, equant quartz crystals that arerecrystallised counterparts of the original grains of the sandstone.
Morphology, physical properties and optical properties
Uranoclite occurs as tightly intergrown aggregates of irregular yellow crystals (Fig. 1). The streak is very pale yellow and the© The Author(s), 2021. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland

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Mineralogical Magazine

Fig. 1. Tightly intergrown uranoclite crystals with gypsum. The field of view is
1.14 mm across.

fluorescence is bright green–white under 405 nm ultraviolet light.
Crystals are translucent with vitreous lustre. The tenacity is brittle
and the fracture is irregular. The mineral is very soft, probably
having a Mohs hardness of ∼1½. Multiple cleavages are likely
but are impossible to define because of the irregular shape ofthe crystals and their occurrence in intergrowths. The density
could not be measured because the mineral is soluble in Clerici
solution and there is insufficient material available for physicalmeasurement. The calculated density based upon the empiricalformula is 4.038 g⋅cm–3. The mineral is soluble in H2O at room
temperature. The occurrence of the mineral in aggregates ofsmall, poorly formed, translucent crystals made the measurementof optical properties impossible. The Gladstone–Dale relationshipusing k(UO3) = 0.118, as provided by (Mandarino, 1976), predicts
an average index of refraction of 1.660.
Raman spectroscopy
Raman spectroscopy was conducted on a Horiba XploRA PLUS
using a 100× (0.9 NA) objective. The spectrum from 4000 to
60 cm–1 obtained using a 532 nm diode laser, 100 μm slit and

439

2400 gr/mm diffraction grating is shown in Fig. 2. The spectrum
from 2000 to 60 cm–1 obtained using a 785 nm diode laser, 100 μm
slit and 1800 gr/mm diffraction grating is shown in Fig. 3.
As far as we know, no reliable vibrational spectroscopy assignments exist in the literature for synthetic uranyl hydroxide chloride phases, except those of Bullock and Parret (1970), forinstance. Thus, the following assignments are based primarily
upon those for uranyl oxide hydroxide hydrate (UOH) minerals
from Čejka (1999) and Frost et al. (2007). All bands in the spectra
were fitted using pseudo-Voigt peak profiles.
In the spectrum obtained using a 532 nm laser, three weakbands with centres at 3606, 3539 and 3366 cm–1 are assigned toν (OH) stretching vibrations. Using the empirically derived equation of Libowitzky (1999), the calculated O⋅⋅⋅O distances of thecorresponding hydrogen bonds are between ∼3.1 Å and ∼2.8 Å,in reasonable agreement with refined O⋅⋅⋅O/Cl bond lengths
determined from the structure refinement. We observed nobands related to ν (OH) stretching vibrations in the high wavenumber region of the spectrum using the 785 nm laser; however,a series of broad and very weak bands related to the ν2 (δ) bending
vibrations of H2O groups are present from ∼1680 to 1640 cm–1.
The additional noisy, broad and very weak bands spanning from∼1530 to ∼1600 cm–1 are possibly related to bending modes (δ)
of U–OH bonds with overlap of ν2 (δ) H2O vibrations from thefour crystallographically unique H2O groups in the structure.
Strong fluorescence in the 532 nm spectrum prevented detailed
analysis of the bands in this region and the remaining assignments
have been made using the fitted bands of the 785 nm spectrum.
A complex series of bands between ∼1400 and ∼1000 cm–1 areassigned tentatively as bending vibrations (δ) U–OH of the bridging hydroxyl groups, possibly overlain with overtones or combination bands. The bands of highest intensity in this region are
centred near 1226, 1189, and include a moderately intense andcomplex doublet near ∼1040 and 1005 cm–1. These assignments
are in line, for instance, with multiple bands observed in thisrange related to (δ) U–OH, librations of H2O and overtones,
found in the calculated spectra of uranopilite (Colmenero et al.,2020). Previously, these bands were generally assigned to stretching modes of SO4 tetrahedra.
The extremely weak band centred at 910 cm–1 is assigned tothe ν3(UO2)2+ antisymmetric stretching vibration, while theFig. 2. The Raman spectrum of uranoclite recordedwith a 532 nm laser. Because of significant fluorescence in the lower wavenumber portion of the spectrum, band assignments in this region are based on
the spectrum recorded with a 785 nm laser (Fig. 3).

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Fig. 3. The baseline corrected and fitted Raman spectrum of uranoclite recorded with a 785 nm laser.

ν1(UO2)2+ symmetric stretching vibration occurs as a very strong
band at 845 cm–1. Bartlett and Cooney (1989) provided an empirical relationship to determine the approximate U–OUr bondlengths from the band position assigned to the UO2+
2 stretchingvibrations, which gives 1.76 Å (ν1) and 1.76 (ν3), in excellent
agreement with the average U–OUr bond lengths from the
X-ray data: 1.77 Å. Frost et al. (2005) provide band positionsfor ν1(UO2)2+ in the synthetic analogue of uranoclite, stating:“Another example is [(UO2)2(OH)2Cl2(H2O)4], with two distinct
uranium atoms in the unit cell and 847.5s, 850s, 852sh, 855vvw(Raman) and 851ms, sharp, 873sh, 883m cm–1 (IR)”; however,no further information is provided and we have located no studies
examining the synthetic phase by Raman or IR. The reported
band positions are comparable to those observed for uranoclite;
however, despite the presence of two symmetrically distinct
uranyl groups, the splitting of ν1(UO2)2 observed by Frost was
not encountered in the spectrum of uranoclite.
A pair of weak bands at 657 and 611 probably arises due tolibration modes of H2O groups, and those at 484 and 454 cm–1
to stretching modes of equatorial U–O bonds or librations of
H2O as well. In other UOH minerals with uranyl hydroxide
sheets, the bands near 400–350 cm–1 are related to various stretching modes of the equatorial OH and O atoms, and the band at
356 cm–1 is assigned as such. A distinct triplet of bands with fitted
centres at 219, 193 and 172 cm–1 may be attributed to ν2(δ)(UO2)2+ bending vibrations and unassigned phonon modes.
Chemical composition
Electron probe microanalyses (6 points on 3 crystals) were performed at the University of Utah on a Cameca SX-100 electron
microprobe with four wavelength dispersive spectrometers andusing Probe for EPMA software. Analytical conditions were
15 kV accelerating voltage, 12 nA beam current and 10 μm

Table 1. Chemical composition of uranoclite.
Constituent

Mean

Range

S.D.

Standard

UO3
Cl
H2O*
O = Cl
Total

79.58
8.95
12.77
–2.02
99.28

78.22–80.83
8.73–9.17

1.06
0.15

syn. UO2
tugtupite*Based upon the known stoichiometry (U = 2 apfu, O+Cl = 12 apfu).
S.D. – standard deviation

beam diameter. Raw X-ray intensities were corrected for matrix
effects with a ϕρ(z) algorithm (Pouchou and Pichoir, 1991). No
other elements were detected. Crystals took a poor polish, butthere was minimal beam damage. Because insufficient material
is available for a direct determination of H2O, it has been
Table 2. Structure details for synthetic (UO2)2(OH)2Cl2(H2O)4 (Huys et al., 2010).
Crystal system: Monoclinic
Space group: P21/n
a = 10.712(2)β = 95.47(3)°b = 6.11212(12)V = 1152.8(4) Å3

Bond lengths (Å)
U1–O1
1.746(10)U1–O2
1.789(10)U1–O102.367(9)U1–O92.382(9)U1–O3
2.397(9)U1–O4
2.490(10)
U1–Cl12.751(3)

U2–O6
U2–O5
U2–O9
U2–O10
U2–O8
U2–O7
U2–Cl2

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1.759(9)1.772(9)2.366(10)2.373(9)2.396(10)2.488(10)2.772(3)c = 17.662(4) Å
Z=4Hydrogen bonds
O3⋅⋅⋅Cl1
3.62(1)O3⋅⋅⋅Cl2
3.11(1)O4⋅⋅⋅Cl1
3.28(1)O4⋅⋅⋅Cl2
3.23(1)O7⋅⋅⋅O1
3.35(1)O7⋅⋅⋅O6
3.03(1)O8⋅⋅⋅O2
3.33(1)O8⋅⋅⋅Cl1
3.08(1)O9⋅⋅⋅O5
2.87(1)O10⋅⋅⋅O2
2.80(1)Mineralogical Magazine

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Table 3. Bond-valence analysis. Values are in valence units.

U1
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
Cl1
Cl2
Sum

1.89
1.72
0.48
0.39

0.49
0.51
0.44
5.92

DonatedH bonds

U2

Accepted
H bonds
0.09
0.18, 0.09

–0.22, –0.10–0.18, –0.17
1.78
1.83
0.39
0.48
0.51
0.50

0.16
0.13
–0.13, –0.09–0.24, –0.09
–0.16
–0.18

0.41
5.90

0.24, 0.17, 0.10
0.22, 0.18

Sum
1.98
1.99
0.16
0.04
1.94
1.96
0.17
0.15
0.84
0.83
0.95
0.81

O
O
H2O
H2O
O
O
H2O
H2O
OH
OH
Cl
Cl

U6+–O bond-valence parameters are from Gagné and Hawthorne (2015). U6+–Cl
bond-valence parameters are from Zachariasen (1978). Hydrogen-bond strengths for
O–H⋅⋅⋅O bonds are based on O–O distances using the relation of Ferraris and Ivaldi (1988).
Hydrogen-bond strengths for O–H⋅⋅⋅Cl bonds are based on H–Cl bond lengths using figure 2
in Malcherek and Schlüter (2007); note that H–Cl bond lengths were approximated bysubtracting 1.0 Å from the O–Cl distance.

calculated based upon the known stoichiometry (U = 2 atoms per
formula unit, O+Cl = 12 apfu). Analytical data are given in
Table 1. The empirical formula is (UO2)2(OH)2.19Cl1.81(H2O)4.
The ideal formula is (UO2)2(OH)2Cl2(H2O)4, which requires
UO3 79.78, Cl 9.89, H2O 12.56, O = Cl –2.23, total 100 wt.%.
X-ray crystallography
The small size, poor quality and intergrown nature of uranoclite
crystals made a single-crystal X-ray diffraction study impossible.
Powder X-ray diffraction (PXRD) data were recorded using a
Rigaku R-Axis Rapid II curved imaging plate microdiffractometerwith monochromatised MoKα radiation. A Gandolfi-like motion
on the w and ω axes was used to randomise the sample. The

pattern provides an excellent match (Fig. 3) with that calculated
from the structure of synthetic (UO2)2(OH)2Cl2(H2O)4 determined by Huys et al. (2010). Observed d values and intensities
were derived by profile fitting using JADE Pro software(Materials Data, Inc.). Data are given in Supplementary Table S1.
Uranoclite is monoclinic with space group P21/n. The unit-cellparameters refined from the powder data using JADE Pro withwhole pattern fitting are a = 10.763(8), b = 6.156(8), c = 17.798(8) Å,
β = 95.656(15)° and V = 1173.5(18) Å3 (Z = 4).
Description of the structure
The crystal structure of uranoclite is presumed to be the same asthat of synthetic (UO2)2(OH)2Cl2(H2O)4 (Huys et al., 2010), as isclearly indicated by the close match between the PXRD of uranoclite and that calculated from the structure of the synthetic material. Some of the important details of the structure of synthetic(UO2)2(OH)2Cl2(H2O)4 and a bond-valence analysis, are provided in Tables 2 and 3. Henceforth, to simplify the wording,we will refer to this as the structure of uranoclite.
The most common coordination polyhedron for U6+ is a squat
pentagonal bipyramid in which the apical vertices are the O atomsof the UO2+
2 uranyl group and the equatorial vertices are also O
atoms that form longer bonds to U. In the structure of uranoclite,
one of the equatorial vertices of each uranyl pentagonal bipyramid
is a Cl anion. This is very unusual among uranyl phases and has
not been reported previously in any mineral structures, although
in nollmotzite (Plášil et al., 2018), F occurs as a ligand in two different U6+ coordinations. The structural unit in uranoclite consists of two pentagonal bipyramids that share an equatorial
OH–OH edge forming a dimer with the same formula as the mineral itself, (UO2)2(OH)2Cl2(H2O)4 (Fig. 4). The Cl anions in the
dimer are in a trans configuration, possibly arranged so due tosteric constraints of the large Cl anions. There is no interstitial
complex in the structure; the dimers are linked to one another
only by hydrogen bonding (Fig. 5).

Fig. 4. Powder X-ray diffraction pattern for uranoclite compared with the lines and simulated pattern calculated from the structure of synthetic (UO2)2(OH)2Cl2(H2O)4(Huys et al., 2010).

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442

Fig. 5. (a) The [(UO2)2(OH)2Cl2(H2O)4] dimer in uranoclite and the synthetic analogue (Huys et al., 2010). Note the colour coding of O, OH, H2O and Cl ligands.
(b) The crystal structure of uranoclite viewed down [010]. Hydrogen bonds are shown as dashed lines with arrows indicating their direction (donor → receptor).
The unit cell is outlined in red. Ligands are colour coded as indicated in (a). The drawing is based on the structure determination for synthetic (UO2)2(OH)2Cl2(H2O)4(Huys et al., 2010).

The cluster in the structure of uranoclite is of the U2L0-type of
Lussier et al. (2016). While there are other mineral structures containing dimers composed of two edge-sharing Uw7 pentagonal bipyramids, such dimers are generally linked by other polyhedra (e.g.
SO4 tetrahedra) to form larger structural units, such as the sheetsof phosphuranylite anion topology (Burns, 2005) found in plášilite(Kampf et al., 2015b) and several other recently described Red
Canyon minerals.
Acknowledgements. Sergey Aksenov and an anonymous reviewer are
thanked for their constructive comments on the manuscript. We are gratefulto retired miner Dan Shumway of Blanding, Utah, for advice and assistancein our collecting efforts in Red Canyon. Funding to JP was provided by the
Czech Science Foundation (20-11949S). This study was also funded by theJohn Jago Trelawney Endowment to the Mineral Sciences Department of
the Natural History Museum of Los Angeles County.
Supplementary material. To view supplementary material for this article,
please visit https://doi.org/10.1180/mgm.2021.33

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