Mineralogical Magazine (2020), 84, 753–765
doi:10.1180/mgm.2020.59

ArticleNatromarkeyite and pseudomarkeyite, two new calcium uranyl
carbonate minerals from the Markey mine, San Juan County,
Utah, USA
Anthony R. Kampf1*, Travis A. Olds2, Jakub Plášil3, Peter C. Burns4 and Joe Marty5

1

Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA; 2Section of Minerals andEarth Sciences, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA; 3Institute of Physics ASCR, v.v.i., Na Slovance 1999/2,
18221 Prague 8, Czech Republic; 4Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA; and55199 East Silver Oak Road, Salt Lake City, UT 84108, USA

Abstract
The new minerals natromarkeyite, Na2Ca8(UO2)4(CO3)13(H2O)24⋅3H2O (IMA2018-152) and pseudomarkeyite, Ca8(UO2)4(CO3)12(H2O)18⋅3H2O (IMA2018-114) were found in the Markey mine, San Juan County, Utah, USA, where they occur as secondary phaseson asphaltum. Natromarkeyite properties are: untwinned blades and tablets to 0.2 mm, pale yellow green colour; transparent; white
streak; bright bluish white fluorescence (405 nm laser); vitreous to pearly lustre; brittle; Mohs hardness 1½ to 2; irregular fracture;
three cleavages ({001} perfect, {100} and {010} good); density = 2.70(2) g cm–3; biaxial (–) with α = 1.528(2), β = 1.532(2) and
γ = 1.533(2); and pleochroism is X = pale green yellow, Y ≈ Z = light green yellow. Pseudomarkeyite properties are: twinned tapering
blades and tablets to 1 mm; pale green yellow colour; transparent; white streak; bright bluish white fluorescence (405 nm laser); vitreous
to pearly lustre; brittle; Mohs hardness ≈ 1; stepped fracture; three cleavages ({101} very easy, {010} good, {100} fair); density = 2.88(2)g cm–3; biaxial (–) with α = 1.549(2), β = 1.553(2) and γ = 1.557(2); and it is nonpleochroic. The Raman spectra of markeyite, natromar2–
keyite and pseudomarkeyite are very similar and exhibit bands consistent with UO2+
2 , CO3 and O–H. Electron microprobe analyses
2+
provided the empirical formula Na2.01Ca7.97Mg0.03Cu0.05(UO2)4(CO3)13(H2O)24⋅3H2O (–0.11 H) for natromarkeyite and Ca7.95(UO2)4(CO3)12(H2O)18⋅3H2O (+0.10 H) for pseudomarkeyite. Natromarkeyite is orthorhombic, Pmmn, a = 17.8820(13), b = 18.3030(4),c = 10.2249(3) Å, V = 3336.6(3) Å3 and Z = 2. Pseudomarkeyite is monoclinic, P21/m, a = 17.531(3), b = 18.555(3), c = 9.130(3) Å,
β = 103.95(3)°, V = 2882.3(13) Å3 and Z = 2. The structures of natromarkeyite (R1 = 0.0202 for 2898 I > 2σI ) and pseudomarkeyite(R1 = 0.0787 for 2106 I > 2σI ) contain uranyl tricarbonate clusters that are linked by (Ca/Na)–O polyhedra forming thick corrugatedheteropolyhedral layers. Natromarkeyite is isostructural with markeyite; pseudomarkeyite has a very similar structure.
Keywords: natromarkeyite, pseudomarkeyite, new mineral, uranyl tricarbonate, crystal structure, markeyite, liebigite, Markey mine, Utah,
USA(Received 8 June 2020; accepted 21 July 2020; Accepted Manuscript published online: 27 July 2020; Associate Editor: Ferdinando Bosi)

Introduction
The mines in the Red Canyon portion of the White Canyon district in south-eastern Utah have yielded many new minerals inrecent years. Most of these are from the Blue Lizard mine on
the east side of Red Canyon; however, the Green Lizard mineand the Giveaway–Simplot mine, also on the east side of Red
Canyon, have yielded new species as well. The vast majority ofthese new species are uranyl sulfates and most, especially fromthe Blue Lizard mine, contain Na. None of the new mineral species from the mines on the east side of Red Canyon contain essential Ca or carbonate. The Markey mine, on the west side of Red
Canyon, has also proven to be a prolific source of new minerals,*Author for correspondence: Anthony R. Kampf, Email: akampf@nhm.org
Cite this article: Kampf A.R., Olds T.A., Plášil J., Burns P.C. and Marty J. (2020)
Natromarkeyite and pseudomarkeyite, two new calcium uranyl carbonate minerals
from the Markey mine, San Juan County, Utah, USA. Mineralogical Magazine 84,753–765. https://doi.org/10.1180/mgm.2020.59

having thus far yielded nine, including natromarkeyite and pseudomarkeyite, described herein (Table 1). All of these containuranyl, most contain carbonate and several contain Ca.
The new minerals and their names were approved by theCommission on New Minerals, Nomenclature and Classificationof the International Mineralogical Association (IMA).
Natromarkeyite (IMA2018-152, Kampf et al, 2019b) is named
as a sodium analogue of markeyite, with two Na in place of one
Ca in the structure. Pseudomarkeyite (IMA2018-114, Kampf
et al., 2019a) is named for its similarity to markeyite. The twominerals occur in intimate association and are similar in appearance, composition, Raman spectra and structure. Note that markeyite (/ma:r ′ ki: ait/) is named for the locality, the Markey mine.
The type specimens for both minerals are deposited in the collections of the Natural History Museum of Los Angeles County, 900
Exposition Boulevard, Los Angeles, CA 90007, USA. The description of natromarkeyite is based on one holotype and one cotype
specimen with catalogue numbers 67487 (holotype) and 67488© Mineralogical Society of Great Britain and Ireland 2020

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Table 1. New minerals from the Markey mine.
MineralFeynmanite*
Leószilárdite
Magnesioleydetite
Markeyite
Meyrowitzite
Natromarkeyite
Pseudomarkeyite
Straβmannite§
Uroxite†FormulaReferenceNa2(UO2)2(SO4)2(OH)2(H2O)7
Na2Mg(UO2)(CO3)3(H2O)3
Mg(UO2)(SO4)2(H2O)7⋅4H2O
Ca9(UO2)4(CO3)13(H2O)22⋅6H2O
Ca3(UO2)3(CO3)6(H2O)10⋅5H2O
Na2Ca8(UO2)4(CO3)13(H2O)24⋅3H2O
Ca8(UO2)4(CO3)12(H2O)18⋅3H2O
Al(UO2)(SO4)2F(H2O)3⋅13H2O(UO2)2(C2O4)(OH)2(H2O)2⋅H2O

[1]
[2]
[3]
[4]
[5]
[6]
[6]
[3]
[7]

*Cotype locality; also found at the Blue Lizard mine, San Juan County, Utah.
§
Cotype locality; also found at the Green Lizard mine, San Juan County, Utah.
†
Cotype locality; also found at the Burro mine, San Miguel County, Colorado.
References: [1] Kampf et al. (2019c); [2] Olds et al. (2017a); [3] Kampf et al. (2019d); [4]Kampf et al. (2018); [5] Kampf et al. (2019e); [6] This study; and [7] Kampf et al. (2020)(cotype). The description of pseudomarkeyite is based on one
holotype specimen, catalogue number 67091, which is also theholotype for markeyite.
Occurrence
Natromarkeyite and pseudomarkeyite were found underground in
the Markey mine, Red Canyon, White Canyon District, San JuanCounty, Utah, USA (37°32′ 57′′ N, 110°18′ 08′′ W). The Markey
mine is located ∼1 km southwest of the Blue Lizard mine, on
the east-facing side of Red Canyon, ∼72 km west of the town ofBlanding, Utah, and ∼22 km southeast of Good Hope Bay on
Lake Powell. The geology of the Markey Mine is quite similar
to that of the Blue Lizard mine (Chenoweth, 1993; Kampf,
et al., 2017), although the secondary mineralogy of the Markey
mine is notably richer in carbonate phases. Underground gas
measurements collected in 2016 using a hand-held Crowcon
Gasman CO2 monitor showed consistently elevated CO2 levels
at the Markey mine, averaging ∼1000 ppm CO2 with a maximum
recorded value of 1600 ppm CO2, levels considerably higher thanat the nearby Blue Lizard mine where carbonate mineral species
are less abundant. Higher CO2 concentration at the Markey
mine may be connected to an abundance of calcite present in
the ores, released by the action of acidic waters derived fromdecaying sulfides.
The following information regarding the history and geology istaken largely from Chenoweth (1993). Jim Rigg of Grand
Junction, Colorado began staking claims in Red Canyon in
March of 1949. The Markey group of claims, staked by Rigg
and others, was purchased by the Anaconda Copper Mining
Company on June 1, 1951. After limited exploration and production, the mine closed in 1955. The mine was subsequently
acquired from Anaconda by Calvin Black of Blanding, Utah
under whose ownership the mine operated from 1960 to 1982
and was a leading producer in the district for nearly that entire
period.
The uranium deposits in Red Canyon occur within the
Shinarump member of the Upper Triassic Chinle Formation, inchannels incised into the reddish-brown siltstones of the underlying Lower Triassic Moenkopi Formation. The Shinarump member consists of medium- to coarse-grained sandstone,
conglomeratic sandstone beds and thick siltstone lenses. Ore
minerals (uraninite, montroseite and coffinite) were depositedas replacements of wood and other organic material and as disseminations in the enclosing sandstone. Since the mine closed in

1982, oxidation of primary ores in the humid underground environment has produced a variety of secondary minerals, mainly carbonates and sulfates, as efflorescent crusts on the surfaces of minewalls.
Natromarkeyite and pseudomarkeyite are very rare minerals inthe secondary mineral assemblage at the Markey mine. They both
occur on asphaltum. Natromarkeyite is associated with andersonite, calcite, gypsum and another new calcium uranyl carbonate
phase that is currently under study. Pseudomarkeyite is associatedwith calcite, gypsum, markeyite (Kampf et al., 2017) andnatrozippeite.
Physical and optical properties
Natromarkeyite
Natromarkeyite crystals are blades and tablets (Fig. 1) up to∼0.2 mm in maximum dimension, flattened on {001} and elongated on [100]. Crystals exhibit the forms {100}, {010}, {001},{110}, {101}, {011} and {111} (Fig. 2). No twinning was observed.
Crystals are pale yellow green and transparent with vitreous topearly lustre. The streak is white. The mineral fluoresces brightbluish white under a 405 nm laser. The Mohs hardness is between
1½ and 2, based upon scratch tests. Crystals are brittle withirregular fracture and three cleavages: perfect on {001}, good on{100} and {010}. At room temperature, the mineral dissolves
very slowly in H2O (minutes) and dissolves immediately witheffervescence in dilute HCl. The density measured by flotation
in a mixture of methylene iodide and toluene is 2.70(2) g cm–3.
The calculated density based on the empirical formula andunit-cell parameters obtained from single-crystal X-ray diffraction
data is 2.695 g cm–3.
Optically, natromarkeyite is biaxial (–), with α = 1.528(2),β = 1.532(2) and γ = 1.533(2) (measured in white light). The 2V,
measured using extinction data collected on a spindle stage andanalysed using EXCALIBRW (Gunter et al., 2004), is 46.5(7)°;the calculated 2V is 53.0°. Dispersion is r > v, weak. The mineralis weakly pleochroic: X = pale green yellow, Y ≈ Z = light green yellow; X < Y ≈ Z. The optical orientation is X = b, Y = a and Z = c.
The Gladstone–Dale compatibility index 1 – (KP/KC) for theempirical formula is –0.015, in the superior range (Mandarino,2007), using k(UO3) = 0.118, as provided by Mandarino (1976).

Fig. 1. Natromarkeyite crystals on holotype specimen (#67487); FOV 0.4 mm across.

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Fig. 2. Crystal drawing of natromarkeyite; clinographic projection in standard
orientation.

Pseudomarkeyite
Pseudomarkeyite crystals are tapering blades and tablets (Fig. 3)
up to ∼1 mm in maximum dimension, flattened on {101} andelongated on [010]. Crystals exhibit the forms {101}, {100},{010} and {510}; the {100} and {510} forms are based uponobserved morphology, but were not measured. Twinning is ubiquitous, by 180° rotation about [101] (Fig. 4).
Crystals are pale green yellow and transparent with vitreous topearly lustre. The streak is white. The mineral fluoresces brightbluish white under a 405 nm laser. The Mohs hardness is ∼1,
based upon scratch tests. Crystals are brittle with stepped fracture.
Cleavage is perfect and very easy on {101}, good on {010} and fairon {100}. Pseudomarkeyite loses birefringence (presumably due
to decomposition), but does not dissolve in room-temperature
H2O; it dissolves immediately with effervescence in dilute HCl.
The density measured by flotation in a mixture of methylene iodide and toluene is 2.88(2) g cm–3. The calculated density based on
the empirical formula and unit-cell parameters obtained fromsingle-crystal X-ray diffraction data is 2.877 g cm–3.
Optically, pseudomarkeyite is biaxial (–), with α = 1.549(2),β = 1.553(2) and γ = 1.557(2) (measured in white light). The 2V
measured directly on a spindle stage is 88(2)°; the calculated 2V
is 89.8°. No dispersion was observed and the mineral is
nonpleochroic. The optical orientation is Y = b, Z ^ a = 30° in
obtuse β (X ≈⊥ {101}). The Gladstone–Dale compatibility index
1 – (KP/KC) for the empirical formula is –0.024, in the excellent
range (Mandarino, 2007), using k(UO3) = 0.118, as provided by
Mandarino (1976).

Fig. 3. Pseudomarkeyite (pearly tapering blades) and markeyite (lustrous blades inupper right) with calcite (brown and grey balls) on asphaltum on the holotype specimen (#67091); FOV 3.5 mm across.

Fig. 4. Crystal drawing of pseudomarkeyite twin; clinographic projection in nonstandard orientation, b vertical.

Raman spectroscopy
Raman spectroscopy was conducted on a Horiba XploRA PLUS
using a 532 nm diode laser. The Raman spectra of natromarkeyite,
pseudomarkeyite and markeyite are very similar. The spectra arecompared in Fig. 5 and the bands are listed in Table 2 with theirlikely band assignments.
The broad multiple bands in the 3700–3100 cm–1 range are
attributed to ν O–H stretching vibrations of structurally
non-equivalent/symmetrically distinct hydrogen-bonded H2Ogroups. According to the correlation given by Libowitzky(1999), this corresponds to approximate O–H⋅⋅⋅O hydrogenbond-lengths between 3.2 and 2.7 Å, which is consistent withwhat we report in the structure determinations. The broad
bands in the 2800–2300 cm–1 range in the markeyite and pseudomarkeyite spectra were originally interpreted as corresponding tostrong (short) hydrogen bonds (Kampf et al., 2018); however, nosuch bonds appear to exist in the structures of markeyite, natromarkeyite or pseudomarkeyite. We now think that this is a spectral artefact because we have also observed it in spectra ofanhydrous minerals and we have recorded other spectra for markeyite that do not exhibit this feature. It is also possible that asmall amount of asphaltum adhering to the crystals caused thebands in this region.
The weak bands between 1439 and 1358 cm–1 can be attributed to the ν3 (CO3)2– antisymmetric stretching vibrations of the(CO3)2– units. Medium to strong multiple bands between 1094

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Fig. 5. The Raman spectra of markeyite, natromarkeyite and pseudomarkeyite.

Table 2. Raman bands and mode assignments for markeyite, natromarkeyite
and pseudomarkeyite.
Markeyite
3700–3300

Natromarkeyite Pseudomarkeyite
3700–3100

2800–2300
1410

1413
1379

Vibrational modes

3700–3300

ν O–H stretching2800–2300

spectral artefacts

1439
1413
1358

ν3 (CO3)2– asym.
stretching

1093
1086
1079

ν1 (CO3)2– sym. stretching

1094
1086
1078
1067

1087
1078
1069

888

893

884

ν2 (δ) (CO3)2– bending orν3 (UO2)2+ asym.
stretching

825

829

826

ν1 (UO2)2+ sym. stretching

752
746

773
756
732

ν4 (δ) (CO3)2– bending(doubly degenerate)

688

691

318
238

336
243

326
238

ν2 (δ) (UO2)2+ bending(split doubly
degenerate)

170
155
127

189
155

174
154
137

lattice modes

772
750
733
698
691

and 1067 cm–1 are connected with the ν1 (CO3)2– symmetricstretching vibrations of several structurally non-equivalent carbonate units (Koglin et al., 1979; Anderson et al., 1980; Čejka,
1999, 2005).
A weak band near 900 cm–1 may be due to the ν2 (δ) (CO3)2–
bending vibrations or to the ν3 (UO2)2+ antisymmetric stretchingvibration; an overlap/coincidence of these two bands is possible.
The very strong bands centred at 825, 829 and 826 cm–1 for markeyite, natromarkeyite and pseudomarkeyite are due to the ν1(UO2)2+ symmetric stretching vibrations and provide inferred U–
O bond lengths around 1.78–1.79 Å (Bartlett and Cooney, 1989).
The ν2 (δ) (CO3)2– bending vibration may coincide with this band.
Several weak to strong bands between 773 and 688 cm–1 areassigned to the doubly degenerate ν4 (δ) (CO3)2– bending vibrations. The medium broad band in the spectra centred near
240 cm–1 is assigned to the split doubly degenerate ν2 (δ)(UO2)2+ bending vibrations. Bands between 189 and 127 cm–1
are due to lattice modes (Koglin et al., 1979; Anderson et al.,
1980; Čejka, 1999, 2005).
Chemical composition
Chemical analyses (five for natromarkeyite and eight for pseudomarkeyite) were performed using a JEOL JXA-8230 electron
microprobe operated in wavelength dispersive mode at 15 kV
and 1 nA, with a 10 μm beam diameter. Matrix effects were
accounted for using the PAP correction routine (Pouchou andPichoir, 1991). For natromarkeyite, a time-dependent intensity
correction was applied to Na. H2O and CO2 were not determined

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Table 3. Chemical composition (in wt.%) for natromarkeyite and pseudomarkeyite.
Natromarkeyite

Pseudomarkeyite

Oxide

Mean

Range

S.D.

Ideal

Mean

Na2O
CaO
MgO
CuO
UO3
CO2*
H2O*
Total

2.35
16.90
0.04
0.15
43.25
21.63
18.35
102.67

2.05–2.67
16.13–17.55
0.00–0.14
0.00–0.36
41.36–45.39

0.30
0.62
0.06
0.15
1.55

2.28
16.53

bdl
17.81
bdl
bdl
45.73
21.11
15.16
99.81

42.17
21.09
17.93

Standard

Range

S.D.

Ideal

17.37–18.41

0.34

17.95

44.01–47.43

1.25

45.78
21.13
15.14

AlbiteWollastonite
Synthetic MgO
Chalcopyrite
Synthetic UO2* Based on the structure.
bdl: below detection limit; S.D. standard deviation.

directly because of extreme paucity of material. The H2O and CO2
contents were calculated by stoichiometry in accord with the crystal structure determinations: based on 4 U, 13 C and 74 O atoms
per formula unit (apfu) for natromarkeyite and 4 U, 12 C and
65 O apfu for pseudomarkeyite. The high analytical total for natromarkeyite is presumably due to the loss of loosely bound H2O
under vacuum resulting in higher concentrations for the remaining
constituents than are to be expected for the fully hydrated phase.
Analytical data are given in Table 3. No other elements with atomic
numbers higher than 8 were above the detection limits.
The empirical formula for natromarkeyite (calculated on thebasis of 74 O apfu) is Na2.01Ca7.97Mg0.03Cu0.05U4.00C13.00O74.00
H53.89 or Na2.01Ca7.97Mg0.03Cu0.05(UO2)4(CO3)13(H2O)24⋅3H2O(–0.11 H). The ideal formula is Na2Ca8(UO2)4(CO3)13(H2O)24⋅
3H2O. The empirical formula for pseudomarkeyite (calculatedon the basis of 65 O apfu) is Ca7.95U4.00C12.00O65.00H42.11, or
Ca7.95(UO2)4(CO3)12(H2O)18⋅3H2O (+0.10 H). The ideal formula
is Ca8(UO2)4(CO3)12⋅21H2O.
X-ray crystallography and structure refinement
Powder X–ray diffraction studies were done using a Rigaku R–Axis
Rapid II curved imaging plate microdiffractometer, with monochromatised MoKα radiation (λ = 0.71075 Å). A Gandolfi-likemotion on the w and ω axes was used to randomise the samples
and observed d values and intensities were derived by profile fitting

Table 4. Data collection and structure refinement details for natromarkeyite and pseudomarkeyite.*Natromarkeyite
Crystal data
Structural formulaSpace group
Unit-cell dimensions (Å, °)V (Å3)
Z
Density (above formula) (g cm–3)
Absorption coefficient (mm–1)
Data collection
Diffractometer
X-ray radiation/power
Temperature (K)Crystal size (μm)
F(000)
θ range (°)
Index ranges

Reflections collected/unique
Reflections with I > 2σI
Completeness to θmax (%)
Max./min. transmission
Refinement
Refinement method
Parameters/restraints
GoF
Final R indices [I > 2σI ]R indices (all data)
Largest diff. peak/hole (e– A–3)

Na2Ca8(UO2)4(CO3)13(H2O)24⋅3H2O
Pmmn
a = 17.8820(13)b = 18.3030(4)c = 10.2249(3)Pseudomarkeyite

3346.6(3)2
2.693
10.419Ca8(UO2)4(CO3)12(H2O)18⋅3H2O
P21/m
a = 17.531(3)b = 18.555(3)c = 9.130(3)β = 103.95(3)2882.3(13)2
2.880
12.059

Rigaku R-Axis Rapid II
MoKα (λ = 0.71075 Å)/50 kV, 40 mA
293(2)
100 × 100 × 30
2548
3.20 to 25.03–21 ≤ h ≤ 21
–21 ≤ k ≤ 21
–12 ≤ l ≤ 1220715/3150; Rint = 0.034
2898
99.4
0.745/0.422

Rigaku R-Axis Rapid II
MoKα (λ = 0.71075 Å)/50 kV, 40 mA
293(2)
120 × 70 × 30
2324
3.04 to 19.96–16 ≤ h ≤ 16
–17 ≤ k ≤ 16
–8 ≤ l ≤ 811253/2772; Rint = 0.12
2106
99.5
0.714/0.326

Full-matrix least-squares on F 2
309/21
1.045
R1 = 0.0202, wR2 = 0.0442
R1 = 0.0234, wR2 = 0.0453+1.58/–0.67

Full-matrix least-squares on F 2
226/0
1.055
R1 = 0.0787, wR2 = 0.2015
R1 = 0.1023, wR2 = 0.2267+4.45/–1.74*Rint = Σ|Fo2–Fo2(mean)|/Σ[Fo2]. GoF = S = {Σ[w(Fo2–F2c )2]/(n–p)}½. R1 = Σ||Fo|–|Fc||/Σ|Fo|. wR2 = {Σ[w(Fo2–F2c )2]/Σ[w(Fo2)2]}½; w = 1/[σ2(Fo2)+(aP)2+bP] where P is [2F2c +Max(Fo2,0)]/3; for natromarkeyite, a is
0.0201 and b is 9.22; for pseudomarkeyite, a is 0.1226 and b is 100.5513.

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Table 5. Atom coordinates, displacement parameters (Å2) and site occupancies for natromarkeyite.
y/b

z/c

Ueq

Occ.

U 11

U 22

U 33

U 23

U 13

U 12

0.46930(2)¼0.44003(4)0.38124(5)¼¼0.4269(2)0.6095(2)¼
0.4388(4)¼
0.40941(15)0.46666(15)0.40536(17)0.55004(14)0.67282(15)0.38786(15)¼0.31061(15)0.4025(4)0.46009(18)0.3875(2)0.5497(2)¼¼0.3132(2)¼
0.3291(2)0.328(3)0.360(2)0.40387(18)0.395(2)0.3675(18)¼¼¼
0.4013(2)0.416(3)0.3633(19)0.4764(3)0.495(4)0.509(4)0.4995(2)0.513(3)0.535(2)¼¼¼¼¼0.6288(5)¼¾0.46718(2)0.43571(4)0.63974(5)¼¾0.6130(2)0.4928(2)0.4033(3)¼
0.7232(6)0.55646(14)0.61501(15)0.67674(14)0.46709(15)0.48721(18)0.47324(16)0.3766(2)0.41739(18)¼0.30954(15)¾¾0.3783(2)0.5567(2)¾0.6545(5)0.52893(18)0.526(3)0.499(2)0.41062(18)0.3682(10)0.433(2)0.6651(3)0.6212(11)0.680(4)0.6617(2)0.629(2)0.677(3)¾¾
0.728(5)0.5811(2)0.5426(17)0.607(2)0.6247(4)0.660(3)0.588(3)¾¼
0.6751(6)¼

0.99124(2)0.07581(2)0.87349(8)0.60892(8)0.6853(4)0.1043(5)0.8739(4)0.8074(4)0.8191(6)0.7774(7)0.5850(12)0.8130(3)0.9792(3)0.8303(3)0.7591(3)0.7470(3)0.0820(3)0.7067(4)0.8838(3)0.6754(6)0.8378(3)0.0924(4)0.8901(5)0.1463(5)0.0074(4)0.5731(5)0.6237(10)0.5187(3)0.4379(19)0.539(4)0.6402(3)0.635(5)0.620(5)0.2660(7)0.267(7)0.340(4)0.3763(3)0.330(4)0.344(5)0.5880(6)0.514(3)0.631(6)0.5816(4)0.614(6)0.578(6)0.7372(8)0.787(7)0.783(8)0.8832(7)0.9275(10)0.6665(9)0.4693(14)0.01533(7)0.01935(7)0.01445(17)0.02310(19)0.0437(10)0.091(2)0.0177(8)0.0205(9)0.0234(13)0.0357(17)0.023(3)0.0215(6)0.0227(7)0.0250(7)0.0227(6)0.0306(7)0.0236(7)0.0310(10)0.0289(7)0.082(3)0.0309(8)0.0287(10)0.0336(11)0.0340(11)0.0313(10)0.0292(10)0.034(2)0.0351(8)
0.042
0.042
0.0337(8)
0.040
0.040
0.0655(18)
0.079
0.079
0.0417(9)
0.050
0.050
0.0415(12)
0.050
0.050
0.0484(10)
0.058
0.058
0.0192(17)
0.023
0.023
0.0428(18)0.115(5)0.154(6)0.213(16)

1
1
1
1
1
1
1
1
1
1
0.5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0.5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0.5
1
1
1
0.5
0.5
0.5
1
1
0.797(19)0.96(5)0.01778(11)0.01172(11)0.0126(4)0.0238(4)0.051(2)0.030(2)0.019(2)0.017(2)0.017(3)0.050(4)0.024(6)0.0283(15)0.0293(16)0.0411(17)0.0127(13)0.0140(13)0.0167(14)0.024(2)0.0130(13)0.161(7)0.047(2)0.027(2)0.028(2)0.030(2)0.028(2)0.017(2)0.021(4)0.050(2)0.01168(11)0.02721(12)0.0130(4)0.0239(4)0.0174(17)0.209(7)0.0146(19)0.024(2)0.029(3)0.020(3)0.017(5)0.0119(13)0.0163(14)0.0108(13)0.0341(16)0.056(2)0.0358(17)0.045(3)0.0475(19)0.023(3)0.0146(14)0.030(2)0.034(2)0.032(2)0.031(2)0.031(2)0.021(4)0.0341(18)0.01652(12)0.01913(13)0.0177(4)0.0216(5)0.062(3)0.034(3)0.019(2)0.020(2)0.024(4)0.037(4)0.027(7)0.0245(16)0.0226(17)0.0230(17)0.0212(16)0.0220(17)0.0183(16)0.024(3)0.0260(18)0.062(4)0.0309(18)0.029(3)0.038(3)0.040(3)0.035(3)0.040(3)0.059(7)0.0217(18)0–0.00579(9)–0.0009(3)–0.0029(3)00–0.0014(16)–0.0003(17)–0.005(3)0–0.001(4)–0.0027(12)0.0000(12)–0.0017(12)–0.0014(13)–0.0126(15)–0.0072(13)–0.013(2)–0.0146(15)0–0.0013(13)000.007(2)–0.001(2)00(4)–0.0025(15)–0.00316(8)0–0.0001(3)–0.0033(4)00–0.0013(17)–0.0009(17)0–0.026(4)0–0.0054(12)–0.0118(13)–0.0145(14)–0.0015(12)0.0027(12)0.0010(12)00.0006(12)–0.084(5)–0.0214(15)0.0025(19)0.012(2)000.0021(19)0–0.0062(16)000.0011(3)0.0054(4)000.0005(17)–0.0003(18)0000.0022(12)0.0009(12)0.0014(13)–0.0025(13)–0.0041(14)–0.0006(13)0–0.0007(14)00.0014(14)
0
0
0
0
0
0
0.0050(16)0.0404(19)0.0338(18)0.0269(19)–0.0007(16)–0.0066(15)0.0053(16)0.049(3)0.040(3)0.107(6)–0.015(3)000.052(2)0.043(2)0.030(2)–0.0039(16)0.0057(17)0.0078(18)0.033(3)0.043(3)0.049(3)00.000(2)00.041(2)0.055(2)0.049(2)0.024(2)0.0172(19)0.0213(19)0.022(4)0.016(4)0.020(5)0.002(3)000.029(3)0.254(17)0.116(8)0.123(15)0.075(5)0.044(5)0.235(12)0.46(4)0.025(4)0.048(6)0.110(8)0.053(10)000.012(7)000–0.016(6)000–0.003(7)0Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/84/5/753/5183700/s0026461x20000596a.pdf

Anthony Kampf et al.

U1
U2
Ca1
Ca2
Na1
Na2
C1
C2
C3
C4
C5
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
OW1
H1A
H1B
OW2
H2A
H2B
OW3
H3A
H3B
OW4
H4A
H4B
OW5
H5A
H5B
OW6
H6A
H6B
OW7
H7A
H7B
OW8
OW9
OW10
OW11

x/a

Mineralogical Magazine

759

Table 6. Atom coordinates and displacement parameters (Å2) for pseudomarkeyite.

Ca1
Ca2
Ca3
Ca4
Ca5
U1
U2
U3
C1
C2
C3
C4
C5
C6
C7
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
O19
O20
O21
O22
O23
O24
O25
OW1
OW2
OW3
OW4
OW5
OW6
OW7
OW8
OW9
OW10
OW11
OW12

x/a

y/b

z/c

Ueq

U 11

U 22

U 33

U 23

U 13

U 12

0.3218(4)0.0353(3)0.1455(5)0.1983(5)0.4234(3)0.25997(7)0.52292(10)0.97059(10)0.2212(19)0.4169(19)0.1409(17)0.4163(16)0.389(3)0.051(2)0.045(2)0.1690(11)0.2906(12)0.2045(11)0.4789(12)0.3649(11)0.3991(10)0.9072(14)0.1235(10)0.2172(12)0.3868(12)0.4708(11)0.3884(12)0.3325(17)0.4260(11)0.9694(13)0.0725(14)0.0599(13)0.0744(16)0.0213(13)0.2755(11)0.2454(12)0.4555(17)0.5971(16)0.0633(17)0.8754(19)0.4398(13)0.164(2)0.2101(14)0.2290(19)0.3429(11)0.0427(13)0.2580(17)0.251(2)0.243(2)0.0902(19)0.4046(12)0.390(3)0.4523(4)0.5605(3)¼¾0.5655(3)0.53908(7)¾¾0.5975(17)0.4919(17)0.5037(16)0.3845(15)¾0.3833(19)¾0.5831(10)0.5777(11)0.6246(11)0.4585(10)0.4992(10)0.5254(10)0.5221(13)0.5321(9)0.5065(12)0.3258(12)0.3827(11)0.4457(11)¾0.6917(10)0.6192(12)0.3209(13)0.4400(12)¾0.8074(12)0.6294(10)0.4476(12)¾¾¾¾0.3822(13)0.6743(19)0.4536(13)¾0.5777(10)0.5698(13)0.3498(16)¼0.167(2)0.1658(17)0.6725(11)¼0.3212(7)0.6980(8)0.9299(11)0.0965(11)0.0674(7)0.67504(14)0.9815(2)0.4935(2)0.937(4)0.697(4)0.410(4)0.086(3)0.125(6)0.666(4)0.817(5)0.817(2)0.938(2)0.053(2)0.702(2)0.573(2)0.811(2)0.698(3)0.526(2)0.416(2)0.115(2)0.022(2)0.119(2)0.176(3)0.096(2)0.473(3)0.734(3)0.754(3)0.948(3)0.736(2)0.629(2)0.724(2)0.804(3)0.161(3)0.460(3)0.529(4)0.444(3)0.301(4)0.111(3)0.827(4)0.260(2)0.983(3)0.408(3)0.162(5)0.904(5)0.073(4)0.496(2)0.534(5)0.0446(18)0.0419(17)0.050(3)0.046(3)0.0371(16)0.0418(5)0.0408(6)0.0457(6)0.046(9)0.047(9)0.040(8)0.034(8)0.075(17)0.059(10)0.039(11)0.040(5)0.049(6)0.042(5)0.044(6)0.042(5)0.033(5)0.064(7)0.033(5)0.054(6)0.053(6)0.041(5)0.045(6)0.047(8)0.037(5)0.058(6)0.071(7)0.058(6)0.044(8)0.057(6)0.042(5)0.055(6)0.051(8)0.044(8)0.053(8)0.065(10)0.067(7)0.120(11)0.067(7)0.069(10)0.042(5)0.064(7)0.094(9)0.096(13)0.150(14)0.109(10)0.047(6)0.104(14)0.037(4)0.032(4)0.045(6)0.032(5)0.031(4)0.0346(9)0.0365(11)0.0418(12)0.053(5)0.034(4)0.044(6)0.029(5)0.030(4)0.0441(9)0.0362(11)0.0367(12)0.042(4)0.057(5)0.055(7)0.069(7)0.046(4)0.0440(10)0.0491(13)0.0529(13)0.001(3)0.003(3)00–0.002(3)–0.0021(6)000.006(3)0.006(3)0.000(5)–0.001(5)0.001(3)0.0042(6)0.0093(9)0.0003(9)0.001(3)–0.001(3)000.002(3)–0.0001(6)00using JADE 2010 software (Materials Data, Inc.). The powder data
are presented in Supplementary Tables S1 and S2 for natromarkeyite and pseudomarkeyite, respectively. These tables, alongwith the crystallographic information files, have been deposited
with the Principal Editor of Mineralogical Magazine and are available as Supplementary material (see below).
The single-crystal structure data were collected at room temperature using the same diffractometer and radiation noted above. The
selection of a crystal of natromarkeyite was straightforward because,
despite their rarity, the natromarkeyite crystals are untwinned andof good quality for single-crystal study. Unfortunately, pseudomarkeyite crystals are invariably twinned (by rotation on [101]) andexhibit high mosaicity. These problems, coupled with the close

spacing of reflections due to the large a and b cell parameters,
made the integration of reflections problematic. The best data
were obtained from a twinned crystal with one larger twin component; however, it proved impossible to adequately separate thereflections from the smaller component during integration. In addition, relatively weak diffraction only provided data to 40°2θ.
For each mineral, single-crystal data were processed using the
Rigaku CrystalClear software package and an empirical (multi–scan) absorption correction was applied using the ABSCOR program (Higashi, 2001) in the CrystalClear software suite. The structures were solved by direct methods using SIR2011 (Burla et al.,2012). SHELXL-2016 (Sheldrick, 2015) was used for the structurerefinements.

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by University of Arizona userAnthony Kampf et al.

760
Table 7. Selected bond distances (Å) and angles (°) for natromarkeyite.

Table 8. Selected bond distances (Å) for pseudomarkeyite.

U1–O12
U1–O11U1–O3 ×2
U1–O10 ×2
U1–O2 ×2
<U1–Oap><U1–Oeq>

1.771(4)1.791(4)2.411(3)2.416(3)2.474(3)
1.781
2.434

Ca1–OW3
Ca1–O5
Ca1–O12
Ca1–O9
Ca1–OW7
Ca1–OW5
Ca1–OW1<Ca1–O>

2.39(2)2.40(2)2.41(2)2.42(2)2.43(3)2.44(2)2.47(2)
2.42

U2–O13U2–O14U2–O8 ×2
U2–O5 ×2
U2–O6 ×2
<U2–Oap><U2–Oeq>1.779(4)1.782(4)2.420(3)2.426(3)2.469(3)
1.781
2.438

Ca1–O8
Ca1–O1
Ca1–O4
Ca1–O10
Ca1–O6
Ca1–O2
Ca1–OW2<Ca1–O>

2.341(3)2.359(3)2.360(3)2.365(3)2.426(3)2.432(3)2.514(3)2.400

Ca2–O17
Ca2–O7
Ca2–O15
Ca2–O1Ca2–O19
Ca2–O8
Ca2–OW6<Ca2–O>

2.31(2)2.36(2)2.36(2)2.37(2)2.50(2)2.51(2)2.58(2)
2.43

Ca3–O16 ×2
Ca3–OW9 ×2
Ca3–OW10 ×2
Ca3–OW8<Ca3–O>

2.34(3)2.35(4)2.39(3)
2.46(4)2.37

Ca4–O18
Ca4–O13
Ca4–O3 ×2
Ca4–OW2 ×2
Ca4–OW4<Ca4–O>

2.27(3)2.29(3)2.37(2)2.52(3)2.64(4)
2.43

Ca5–O2
Ca5–O14
Ca5–O12
Ca5–O6
Ca5–O11
Ca5–O4Ca5–OW5<Ca5–O>

2.35(2)2.35(2)2.38(2)2.39(2)2.40(2)2.41(2)2.51(2)2.40

Ca2–O16 ×½
Ca2–O15
Ca2–OW6
Ca2–O3
Ca2–OW1
Ca2–OW4
Ca2–O1Ca2–OW5
Ca2–OW7 ×½<Ca2–O>2.3671(15)2.385(2)2.389(3)2.402(3)2.416(3)2.439(4)2.633(3)2.649(3)2.702(4)2.481

Na1–OW11
Na1–O7 ×2
Na1–OW9
Na1–O9 ×2<Na1–O>

2.208(15)2.327(5)2.477(11)2.729(8)2.466

Na2–OW8
Na2–OW3 ×2
Na2–O11 ×2<Na2–O>

2.261(9)2.269(7)2.462(4)
2.345

C1–O1
C1–O2
C1–O3
<C1–O>

1.247(5)1.292(5)1.306(5)
1.282

C2–O4
C2–O6
C2–O5
<C2–O>

1.263(5)1.291(5)1.294(5)
1.283

C3–O7
C3–O8 ×2
<C3–O>

1.249(7)1.296(4)
1.280

C4–O9
1.228(8)C4–O10 ×2 1.309(4)<C4–O>
1.282
C5–O15 ×2 1.238(6)C5–O161.319(14)<C5–O>
1.265

Hydrogen bonds (D = donor O, A = acceptor O)
D–H
OW1–H1A
OW1–H1BOW2–H2A
OW2–H2BOW3–H3A
OW3–H3BOW4–H4A
OW4–H4B
OW5–H5A
OW5–H5B
OW6–H6A
OW6–H6B
OW7–H7A
OW7–H7B
OW8
OW8
OW9
OW10
OW10
OW11

D–H
0.828(19)0.811(19)0.794(19)0.792(19)0.80(2)0.81(2)0.805(19)0.806(19)0.83(2)0.83(2)0.814(19)0.797(19)0.82(2)0.81(2)

H⋅⋅⋅A

D⋅⋅⋅A

1.90(2)2.07(2)2.21(2)2.50(2)2.422(17)2.732(4)2.832(5)2.962(4)2.902(5)3.114(6)

176(5)
157(5)
159(5)
113(4)
145(1)

2.07(2)2.19(3)2.869(4)2.933(5)

170(6)
153(5)

2.38(4)2.13(3)2.27(3)
1.92(2)2.36(7)

3.153(10)2.909(5)3.010(11)2.736(8)3.030(9)3.259(6)3.177(11)3.243(8)3.018(11)3.053(10)2.917(12)155(7)
159(6)
154(6)
172(9)
139(8)

<DHA

A
O5
OW2
O9
O7
O5 ×2*
none
O4
OW3
none
OW10
O4
OW10
OW8
O14
O11
O16
O13 ×2O12
O13
OW10 ×2* The H3B site is split into two symmetrically related, half-occupied sites, each of whichbonds to an O5 atom.

For natromarkeyite, all non-hydrogen atoms were successfullyrefined with anisotropic displacement parameters. DifferenceFourier synthesis located the hydrogen atom positions related
to OW1 to OW7; however, no geometrically reasonable H positions could be found for OW8 to OW11. This could be becauseof disorder for these H2O groups. The located H-atom positions
were refined with soft restraints of 0.82(2) Å on the O–H distances and 1.30(2) Å on the H–H distances and with the Ueq
of each H set to 1.2 times that of its donor O atom.
Hydrogen bonds for OW8 to OW11 are proposed based upon
O–O distances and geometries. It should be further noted
that, because of the presence of considerable unresolved residual
electron density, the assignment of H atom positions related to
OW1 to OW7 was difficult and some anomalies suggest thatseveral assignments are questionable: (1) The distance between
the H1B and H2B sites is unusually short (1.47 Å), so that at

C1–O3
C1–O2
C1–O1
<C1–O>

1.27(3)
1.27(3)
1.28(3)
1.27

C2–O4
C2–O5
C2–O6
<C2–O>

1.24(3)
1.28(3)1.32(3)
1.28

C3–O7
C3–O8
C3–O9
<C3–O>

1.23(3)1.29(3)
1.33(3)
1.28

C4–O11
C4–O10C4–O12<C4–O>

1.23(3)
1.26(3)1.30(3)
1.26

C5–O13C5–O14 ×2<C5–O>

1.19(6)1.32(4)
1.28

C6–O15C6–O17
C6–O16<C6–O>

1.23(4)1.31(4)1.32(4)1.29

C7–O18C7–O19 ×2<C7–O>

1.18(4)1.30(3)
1.26

U1–O20U1–O21
U1–O5
U1–O9
U1–O1
U1–O2
U1–O8
U1–O6
<U1–Oap><U1–Oeq>1.77(2)
1.79(2)2.37(2)2.38(2)2.43(2)2.43(2)2.45(2)2.47(2)
1.78
2.42

U2–O22
U2–O23U2–O10 ×2
U2–O14 ×2
U2–O11 ×2<U2–Oap><U2–Oeq>1.76(3)
1.83(3)2.43(2)2.45(2)2.47(2)
1.80
2.45

U3–O24U3–O25
U3–O16 ×2
U3–O19 ×2
U3–O15 ×2<U3–Oap><U3–Oeq>1.72(3)
1.78(3)2.42(2)2.42(2)2.43(2)1.75
2.42

least one of these sites may be incorrect; (2) the OW7–
H7A⋅⋅⋅OW8 hydrogen bond, with a bond strength of 0.21
valence units, seems unlikely because OW8 would be highly
oversaturated in bond strength; and (3) at least one of thethree hydrogen bonds received by OW10 is probably incorrect
because it is otherwise very oversaturated.
For pseudomarkeyite, all atoms were located and successfullyrefined at full occupancies to provide a very reasonable structure
model; however, because of the aforementioned problems, only
the Ca and U atoms could be refined with anisotropic displacement parameters and hydrogen atom sites could not be located.
While the general structure is clearly correct, the aforementioned
twinning and high mosaicity led to some bond-length anomalies,
which we consider refinement artefacts. In particular, some bondlengths are significantly shorter than normal: C5–O13 (1.19 Å),C7–O18 (1.18 Å) and U3–O24 (1.72 Å).
Data collection and refinement details are given in Table 4. Atom
coordinates and displacement parameters are given in Tables 5 and
6 for natromarkeyite and pseudomarkeyite, respectively. Selectedbond distances are in Tables 7 and 8 for natromarkeyite and pseudomarkeyite, respectively. Bond-valence analyses are in Tables 9 and
10 for natromarkeyite and pseudomarkeyite, respectively. Note thatthe bond-valence analysis for pseudomarkeyite does not includehydrogen-bond contributions because of the difficulty in proposing
an unambiguous hydrogen-bonding scheme for such a complex
structure without hydrogen atom positions.

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761

Table 9. Bond valence analysis for natromarkeyite. Values are expressed in valence units.*

O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
OW1
OW2
OW3
OW4
OW5
OW6
OW7
OW8
OW9
OW10
OW11
Sum

Ca1

Ca2

0.33
0.28

0.17

Na1

Na2

U1

U2

0.33
0.22×2↓

0.16×2↓

C5

DonatedH bonds

0.15×2
0.14×2

1.53
1.24×2↓

0.46×2↓1.71
1.79

0.10×2
0.13×2
0.12×2
0.12

1.76
1.75
×½↓

0.31×2→
0.33×2→0.29

1.50×2↓1.22
0.25×2↓0.27
0.16×2→0.31
×½↓
0.14×2→
0.26
0.16

2.13

2.05

1.08

0.10
–0.21, –0.17–0.14, –0.15–0.11, –0.20–0.16, –0.14–0.11, –0.20–0.15, –0.13–0.21, –0.12–0.10, –0.10–0.10, –0.10–0.13, –0.12–0.15, –0.15

0.23

0.30
1.08

6.14

Accepted
H bonds

0.16, 0.15
0.21, 0.11

0.09×2↓
0.33

C4

1.45
1.29×2↓0.45×2↓

0.35

C3

1.40
1.31
1.29

0.45×2↓
0.41×2↓

0.28

C2

1.46
1.31
1.25

0.40×2↓
0.46×2↓

0.30

C1

6.13

4.02

4.00

4.03

4.01

0.17
0.14

0.21
0.11, 0.13, 0.15

Sum
1.96
1.99
2.02
2.05
2.08
1.99
1.98
2.09
1.89
2.03
2.07
2.04
2.00
1.87
2.12
1.97
–0.10
0.11
0.09
–0.03
0.02
0.03
–0.05
0.27
–0.04
0.14
0.00

4.23

* Multiplicity is indicated by ×↓→. Bond-valence parameters from Gagné and Hawthorne (2015); hydrogen-bond strengths based on O–O bond lengths from Ferraris and Ivaldi (1988).
Donated hydrogen-bond strengths are shown as negative values. There was no obvious hydrogen-bond receptor for one H atom of the OW3 and the OW5 group; assuming that these H atoms
donate multiple weak hydrogen bonds, a donated bond strength of –0.20 (shown in italics) is assigned to OW3 and OW5.

Description and discussion of the structures
The structures of markeyite, natromarkeyite and pseudomarkeyite
are constructed of similar components. The U sites in the structures are surrounded by eight O atoms forming a squat UO8 hexagonal bipyramid. These bipyramids are each chelated by three
CO3 groups, forming a uranyl tricarbonate cluster (UTC) of formula [(UO2)(CO3)3]4– (Fig. 6). As noted by Burns (2005), UTCsare especially common structural features in uranyl carbonatesthat crystallise from alkaline solutions.

Natromarkeyite
Two independent U sites (U1 and U2) in the structure of natromarkeyite centre two UO8 hexagonal bipyramids, which combinewith CO3 groups centred by four independent C sites (C1, C2, C3
and C4) to form two different UTCs. As was noted in the structure of markeyite, there is an additional CO3 group (centred by
C5) that is not chelated to a UO8 hexagonal bipyramid. The
C5O3 group is half-occupied, shares an O15–O15 edge with anequivalent C5O3 group and is completed by a half-occupied
O16 site. Due to steric limitations, only one of the adjacent C5
sites can be occupied at the same time. Another half-occupiedO site (OW7) is located 1.28 Å from the O16 site and cannot
be occupied when the O16 site is occupied. There are two different Ca–O polyhedra in the structure. Ca1 bonds to seven fully
occupied O sites, Ca2 bonds to seven fully occupied and two halfoccupied O sites for a total effective coordination of eight. The
Na1 occupies a position equivalent to the Ca3 site in the markeyite structure, while the Na2 site has no counterpart in themarkeyite structure. Na1 is octahedrally coordinated to five fully
occupied O sites and one O site (OW11) with a refined occupancy
of 0.96 that can be considered essentially fully occupied. Na2bonds to five fully occupied O sites forming a Na2O5 trigonal
bipyramid.
The two Ca–O polyhedra share edges and corners with theUTCs in very different ways. The Ca1O7 polyhedra share edges
with U1 and U2 bipyramids and corners with C1O3 and C2O3 triangles in different UTCs. Pairs of Ca2O8 polyhedra share an edge
to form a dimer, which is linked to a second dimer through thehalf-occupied C5O3 triangles and OW7 sites. The group of four
Ca2O8 polyhedra (with the C5O3 triangle at its centre) is linked
to two U1 UTCs by edge sharing between Ca2O8 polyhedra
and C1O3 triangles. The Na1O6 octahedra share corners with
two C3O3 and two C4O3 triangles, each belonging to independent
UTC units. The Na2O5 trigonal bipyramids share their apicalvertices (O11) with apical (uranyl) vertices of two symmetricallyrelated U1 hexagonal bipyramids. The linkages between the
Ca and Na polyhedra and the UTCs form thick corrugatedheteropolyhedral layers parallel to {010} (Fig. 7) and these layers
link to one another and to interlayer H2O groups (OW10) only
via hydrogen bonds (Fig. 8). This explains the perfect {010}cleavage.
As noted above, the Na2 site in the natromarkeyite structure
has no counterpart in the markeyite structure. The OW3 andOW8 groups, which are coordinated to Na2 in natromarkeyite,
are interlayer H2O sites in markeyite. Additionally, there is a partially occupied OW12 site bonded to Ca3 in the markeyite structure, which has no counterpart in the natromarkeyite structure.
Summing the H2O site occupancies in the two structures provides

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762
Table 10. Bond valence analysis for pseudomarkeyite. Values are expressed in valence units.*
Ca1
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
O19
O20
O21
O22
O23
O24
O25
OW1
OW2
OW3
OW4
OW5
OW6
OW7
OW8
OW9
OW10
OW11
OW12
Sum

Ca2

Ca3

Ca4

Ca5

U1

0.34

0.44
0.44

0.32

U2

U3

C1

0.29
0.31
0.33
0.23

0.29

C6

C7

1.41
1.52
1.28

0.39

1.68
1.22×2↓

0.43×2↓

0.34

C5

1.52
1.31
1.19
0.44×2↓
0.41×2↓

0.30
0.31

C4

1.49
1.34
1.22

0.50
0.41
0.43
0.49

0.29

C3

1.34
1.38
1.38

0.32×2↓0.30

C20.44×2↓0.45×2↓0.33
0.35×2↓

1.52
1.22
1.25

0.37
0.41

1.73
1.28×2↓0.45×2↓

0.23
1.79
1.72
1.83
1.58

1.99
1.75
0.25
0.22×2↓
0.31
0.17
0.27

0.23
0.19

0.28
0.26
0.34×2↓
0.31×2↓

1.99

2.01

2.24

2.06

2.12

6.32

5.96

6.45

4.10

4.05

4.02

4.21

4.12

3.99

Sum
2.10
2.16
1.70
1.78
2.14
1.94
1.85
1.97
1.97
1.85
2.23
1.88
2.07
1.99
2.29
2.02
1.62
2.14
1.96
1.79
1.72
1.83
1.58
1.99
1.75
0.25
0.22
0.31
0.17
0.50
0.19
0.28
0.26
0.34
0.31
0.00
0.00

4.29

* Multiplicity is indicated by ×2↓. Bond valence parameters from Gagné and Hawthorne (2015). Hydrogen-bond contributions are not included.

27.30 H2O pfu (ideally 27) for natromarkeyite and 28.25 H2O pfu(ideally 28) for markeyite. Expressing the structurally bound H2Ogroups (those bonded to cations) separately from the isolated
H2O groups (those linked only via hydrogen bonds), results in

the ideal formulas Ca9(UO2)4(CO3)13(H2O)22⋅6H2O for markeyite and Na2Ca8(UO2)4(CO3)13(H2O)24⋅3H2O for natromarkeyite. In spite of their minor structural differences, markeyite
and natromarkeyite are considered essentially isostructural.

Pseudomarkeyite

Fig. 6. The uranyl tricarbonate cluster (UTC) of formula [(UO2)(CO3)3]4– consisting of asquat UO8 bipyramid and three CO3 groups sharing alternating UO8 equatorial edges.

The three U sites (U1, U2 and U3) in the structure of pseudomarkeyite centre three UO8 hexagonal bipyramids, which coordinate
to CO3 groups centred by seven independent C sites (C1 to C7) toform three different UTCs. There is no additional non-UTC CO3
group in the pseudomarkeyite structure. Five Ca–O polyhedra
share edges and corners with the UTCs. The UTCs and Ca–O
polyhedra form thick corrugated heteropolyhedral layers parallelto {101}. These layers are very similar to the layers in markeyite(Fig. 6), but differ in several respects. The most obvious differenceis that the pseudomarkeyite layer is missing the distinctive grouping of four Ca2 polyhedra (and C5 triangle) found in the markeyite layer. Viewed down the b axis (Fig. 8), another importantdifference in the structures is evident. In the markeyite structure,
the heteropolyhedral layers link to one another and to interlayer
H2O groups only via hydrogen bonds; however, in the pseudomarkeyite structure, the layers are linked through edge and cornerlinks to Ca polyhedra.

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Mineralogical Magazine

763

Fig. 7. The heteropolyhedral layers in markeyite, natromarkeyite and pseudomarkeyite. The polyhedra are labelled and for natromarkeyite the H atoms are shownas small white spheres. The unit cells are outlined with dashed lines.

Fig. 8. The structures of markeyite, natromarkeyite and pseudomarkeyite viewed down [010] with heteropolyhedral layers horizontal. The polyhedra are labelled,
the O atoms of the isolated H2O groups are shown as large white spheres and H atoms for natromarkeyite are shown as small white spheres. The unit cells are
outlined with dashed lines.

Fig. 9. Heteropolyhedral layer in the structure ofliebigite viewed down [010]. The unit cell is outlinedwith dashed lines.

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764
Table 11. Information measures for selected uranyl carbonates.
Mineral

V
(Å3)

v

IG
(bits/atom)

IG,total(bits/cell)

Ichem, norm.
(bits/formula/Z )Liebigite
Pseudomarkeyite
Natromarkeyite
Markeyite

4015.82882.33346.63356.6

200
270
302
340

5.664
6.218
5.583
5.833

1132.77
1678.74
1686.00
1938.199.90
114.21135.54134.27v = number of atoms in the reduced unit cell.
IG = structural information content.
Ichem = chemical information content normalised by Z.

Another interesting contrast relates to the edges shared
between UO8 bipyramids and Ca polyhedra. Note that in any
UTC, the UO8 bipyramid has three equatorial edges that are
not shared with CO3 groups. In the markeyite and natromarkeyite
structures, each of the two UO8 bipyramids shares two of theseequatorial edges with Ca polyhedra, the third equatorial edge
being unshared. In the pseudomarkeyite structure, the U1 andU3 bipyramids share all three available non-CO3 equatorial
edges with Ca polyhedra, while the U2 bipyramid shares only
two such edges.
Comparison with other structures
Lussier et al. (2016) provide a review of inorganic uranyl compounds that includes specifics of the structures of uranyl carbonate
minerals. Their review shows the UTC structural unit to be a prominent feature in the majority of uranyl carbonate minerals. In thesestructures, the UTCs are linked by various combinations of countercations and hydrogen-bonding networks as 0-dimensional clusters.
These are usually incorporated into heteropolyhedral sheets, suchas in the minerals liebigite (Mereiter, 1982), grimselite (Plášil
et al., 2012) and línekite (Plášil et al., 2017). There are also complex
clusters, such as those in ewingite (Olds et al., 2017b) and paddlewheelite (Olds et al., 2018), which combine UTCs with otherbuilding units, such as the trimers of uranyl polyhedra in ewingite
and the square–pyramidal copper polyhedra in paddlewheelite.
Less commonly, the structural units in uranyl carbonate minerals
are infinite sheets of uranyl polyhedra and carbonate triangles,
such as in rutherfordine (Finch et al., 1999), fontanite (Hughes
and Burns, 2003), sharpite (Plášil, 2018) and meyrowitzite(Kampf et al., 2019e), and sheets containing also lanthanidecentred polyhedra, such as in bijvoetite-(Y) and kamotoite-(Y)(Plášil and Petříček, 2017).
The uranyl carbonate mineral with which the structures ofmarkeyite, natromarkeyite and pseudomarkeyite are most similar
is liebigite, Ca2(UO2)(CO3)3⋅11H2O (Mereiter, 1982). All four
structures contain the same structural components and thesame types of polyhedral linkages. In all four, the Ca–O polyhedra
link the UTCs forming thick corrugated heteropolyhedral layers.
In the structure of liebigite, as in those of markeyite, natromarkeyite and natromarkeyite, these layers link to one another andto interlayer H2O groups only via hydrogen bonds; however,
the topology of the layer in liebigite (Fig. 9) is quite different
from those in markeyite, natromarkeyite and pseudomarkeyite.
Structural complexity
We examined the structural complexity of markeyite, natromarkeyite and pseudomarkeyite, as well as that of the related

mineral liebigite. As developed by Krivovichev (2012, 2013,2014, 2018), structural complexity can be quantified as the total
structural information content, IG,total. As available structure
determinations of liebigite, markeyite and pseudomarkeyite lack
H atom positions, the approximate calculations of the fictive H
atoms contribution to the total structure complexity were undertaken. An overview of the structural and chemical complexity
measures of the four minerals, calculated using the program
TOPOS (Blatov et al., 2014), is given in Table 11.
Both structurally and chemically, the least complex is liebigite,which represents a ‘relatively simple’ layered structure. The structures of markeyite, natromarkeyite and pseudomarkeyite are significantly more complex, owing to the additional linkages (e.g.
the Ca2–C5O3–C5O3–Ca2 linkages in markeyite). These threestructures are nearly as complex as the suite of complex uranyl
carbonate structures based upon ‘paddle-wheel’ units, whichhave IG,total >2000 bits/unit cell: braunerite, K2Ca(UO2)(CO3)3⋅6H2O (Plášil et al., 2016), línekite, K2Ca3[(UO2)(CO3)3]2⋅7H2O (Plášil et al., 2017) and paddlewheelite,
MgCa5Cu2(UO2)4(CO3)12⋅33H2O (Olds et al., 2018). The moststructurally complex uranyl carbonate mineral, ewingite,
Mg8Ca8(UO2)24(CO3)30O4(OH)12⋅180H2O (Olds et al., 2017b),
is also the most structurally complex mineral known.
Given the similarities in the structures of markeyite, natromarkeyite and pseudomarkeyite, it is not surprising that theirstructural complexities are very similar. The chemical complexity(Ichem, norm.) of natromarkeyite is somewhat higher due to incorporation of an additional cation in the structure. These minerals
certainly form under similar conditions, although natromarkeyite
is found in in assemblages more enriched in Na, typically including the mineral andersonite.
Supplementary material. To view supplementary material for this article,
please visit https://doi.org/10.1180/mgm.2020.59
Acknowledgements. Reviewers Fernando Cámara and Igor V. Pekov arethanked for their constructive comments on the manuscript. A portion ofthis study was funded by the John Jago Trelawney Endowment to theMineral Sciences Department of the Natural History Museum of Los
Angeles County. This research was also financially supported by the Czech
Science Foundation (project 20-11949S to J.P.).

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