1685
The Canadian Mineralogist
Vol. 39, pp. 1685-1689 (2001)

OSWALDPEETERSITE, (UO2)2CO3(OH)2•4H2O, A NEW BASIC
URANYL CARBONATE MINERAL FROM THE JOMAC URANIUM MINE,SAN JUAN COUNTY, UTAH, U.S.A.
RENAUD VOCHTEN§
Department of Subatomic and Radiation Physics, Division of Nuclear Material Physics,
Universiteit Gent, Proeftuinstraat 86, B-9000 Gent, Belgium

MICHEL DELIENS
Institut royal des Sciences naturelles de Belgique, Section de Minéralogie et de Pétrographie,
Rue Vautier 29, B-1000 Bruxelles, Belgium

OLAF MEDENBACH
Institut für Mineralogie, Ruhr-Universität Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany

ABSTRACT
Oswaldpeetersite, ideally (UO2)2CO3(OH)2•4H2O, is a newly discovered hydrated basic uranyl carbonate mineral found inthe Jomac uranium mine, Brown’s Rim, San Juan County, Utah, U.S.A. It occurs along some bedding planes of a layer of siltstone
within the Triassic Shinarump conglomerate. Associated minerals are gypsum, cuprite, antlerite, goethite, lepidocrocite,
mbobomkulite, hydrombobomkulite, sklodowskite and two undefined uranium minerals. Oswaldpeetersite occurs as micrometricprismatic crystals (approximately 0.1  0.01  0.002 mm). These are canary yellow and transparent, with a vitreous luster andpale yellow streak. It does not fluoresce in ultraviolet radiation. The HMohs is in the range 2–3. Dmeas > 4.10 g/cm3, Dcalc = 4.54 g/
cm3 (empirical formula), 4.50 g/cm3 (idealized formula). Optically biaxial negative,  1.583(2),  1.669(2),  1.712(2), and 2Vcalc= 67.4(2)°. Orientation Z || a and elongation positive. The pleochroism is X and Y very pale yellow to colorless, and Z pale yellow.
The cleavage and parting are along the elongation. The tenacity is weak, and the fracture, uneven. The habit can be described asacicular. Oswaldpeetersite is monoclinic, P21/c, with unit-cell parameters refined from powder data: a 4.1425(6), b 14.098(3), c18.374(5) Å,  103.62(1)°, V 1042.8(3) Å3, a:b:c = 0.2938:1:1.3033 and Z = 4. The forms recognized are {100}, {010} and{001}. The strongest eight reflections of the X-ray powder pattern [d(in Å)(I)(hkl)] are: 8.95(65)(002), 7.54(63)(012),
4.55(96)(031), 4.26(60)(014), 3.46(62)(015), 3.32(100)(1̄14), 3.029(85)(043) and 2.273(62)(062). Electron-microprobe andthermogravimetric analyses gave UO3 81.47 and H2O 12.30 wt.%. The CO2 content was calculated as 6.23 wt.% by difference.
The oxide formula is 2.03 UO3•1.01 CO2•4.88 H2O, and the empirical formula is (UO2)2.03(CO3)1.01(OH)2.05•3.85 H2O. The namehonors the Belgian structural crystallographer Maurice Oswald Peeters, University of Leuven, Belgium.
Keywords: oswaldpeetersite, new mineral species, basic uranyl carbonate hydrate, X-ray data, Jomac mine, San Juan County,Utah, U.S.A.

SOMMAIRE
L’oswaldpeetersite, de formule idéale (UO2)2CO3(OH)2•4H2O, est un carbonate basique hydraté d’uranyle découvert
récemment dans la mine d’uranium Jomac, Brown’s Rim, comté de San Juan, Utah, aux Etats-Unis. Le minéral se rencontre danscertains plans de stratification d’une couche d’argilite, au sein du conglomérat triassique de Shinarump. L’association minérale
est constituée de gypse, cuprite, antlerite, goethite, lepidocrocite, mbobomkulite, hydrombobomkulite, sklodowskite et deuxminéraux uranifères indéfinis. Les cristaux prismatiques sont jaune canari et transparents avec un éclat vitreux. La rayure est
jaune pâle. Le minéral n’est pas fluorescent aux rayons ultraviolettes. La dureté HMohs est entre 2 et 3. Dmes > 4,10 g/cm3, Dcalc =4,54 g/cm3 (formule empirique), 4,50 g/cm3 (formule idéale). Optiquement biaxe négative,  1,583(2),  1,669(2),  1,712(2) et2Vcalc = 67,4(2)°, avec orientation optique Z || a et allongement positif. Le pléochroïsme des cristaux est: X et Y jaune très pâle, Zjaune pâle, et le clivage est selon l’allongement. Les cristaux montrent un habitus aciculaire. La tenacité est faible, et la cassure,irrégulière. L’oswaldpeetersite est monoclinique, groupe spatial P21/c, avec les paramètres de la maille affinés à partir des données
sur poudre: a 4,1425(6), b 14,098(3), c 18,374(5) Å,  103,62(1)°, V 1042,8(3) Å3, a:b:c = 0.2938:1:1.3033 et Z = 4. Les formes§

E-mail address: revo@nets.ruca.ua.ac.be1685 39#6-déc-01-2290-13

1685

21/12/01, 12:48

1686

THE CANADIAN MINERALOGISTdes cristaux sont {100}, {010} et {001}. Les huit raies les plus intenses du spectre de diffraction X [d(en Å)(I)(hkl)] sont:
8,95(65)(002), 7,54(63)(012), 4,55(96)(031), 4,26(60)(014), 3,46(62)(015), 3,32(100)(1̄14), 3,029(85)(043) et 2,273(62)(062).
L’analyse chimique à la microsonde électronique et par thermogravimétrie a donné: UO3 81,47 et H2O 12,30%. La quantité deCO2, obtenue par différence, est 6,23%. La formule en termes d’oxydes correspond à 2,03 UO3•1,01 CO2•4,88 H2O, et la formule
empirique est (UO2)2,03(CO3)1,01(OH)2,05•3,85H2O. Le nom du minéral souligne les contributions du cristallographe structural
Maurice Oswald Peeters de l’Université de Leuven, Belgique.
Mots-clés: oswaldpeetersite, nouvelle espèce minérale, carbonate basique hydraté d’uranyle, données de diffraction X, mine
Jomac, comté de San Juan, Utah, Etats-Unis.

INTRODUCTION

MORPHOLOGY AND PHYSICAL PROPERTIES

Up to now, only three uranyl carbonates without
additional cations have been described as minerals:
rutherfordine, UO2CO3 (Marckwald 1906), joliotite,
UO2CO3•2H2O (Walenta 1976) and blatonite, UO2CO3•
H2O (Vochten & Deliens 1998).
Oswaldpeetersite, ideally (UO2)2CO3(OH)2•4H2O, isthe first known basic uranyl carbonate mineral devoidof other cations in its structure. This mineral was discovered at the Jomac uranium mine, Brown’s Rim, SanJuan County, Utah, U.S.A., by Patrick Haynes, ofCortez, Colorado, geologist and mineral collector. After haynesite, (UO2)3(SeO3)2(OH)2•5H2O (Deliens &Piret 1991), and blatonite, UO2CO3•H2O (Vochten &Deliens 1998), oswaldpeetersite is the third new uranium-bearing mineral species originating from theJomac uranium mine. The Jomac mine was initially(1950–1979) owned by Alliance Nuclear Inc. of Spokane, Washington, and then (1983–1985) by Birco Development of Moab, Utah. The mines of the district,including the Jomac mine, are now closed and are partof the Glen Canyon National Recreation Area.
The Commission on New Minerals and Mineral
Names, IMA, approved oswaldpeetersite in October2000 (IMA 2000–34). Type material is deposited in themineralogical collection of the Royal Belgian Instituteof Natural History, Brussels, Belgium, under catalogue
number R.C. 5166. The mineral name honors Maurice
Oswald Peeters (b. 1945), structural crystallographer at
the University of Leuven, Belgium, and researcher inthe field of uranium mineralogy.

Oswaldpeetersite most commonly occurs as micrometric prismatic crystals arranged in radiating groups,
rarely distributed on layers of gypsum. The dimensionsof the crystals are approximately 0.1  0.01  0.002
mm. SEM photomicrographs (Figs. 1A, B), taken at two
different magnifications, show typical arrangements ofthe crystals, which are heavily striated lengthwise. Theforms recognized are {100}, {010} and {001}. The
habit can be described as acicular. The mineral is canary yellow, transparent with a vitreous luster and a paleyellow streak. The Mohs hardness is estimated to be
between 2 and 3, the cleavage and the parting are along
the elongation, the tenacity is weak, and the fracture isuneven. A density greater than 4.10 g/cm3 was foundusing the flotation method at 25°C in Clerici solution.
The calculated density, based on the empirical formula,is 4.54 g/cm3, and that based on the idealized formula is4.50 g/cm3. Oswaldpeetersite is soluble with effervescence in dilute HCl.

OCCURRENCE
The rock in which oswaldpeetersite occurs belongs
to the Triassic Shinarump conglomerate, which is richin organic material such as black coal-bearing smears
and logs of partially petrified wood. Coconinoite is themost common U6+-bearing mineral at the Jomac mine
and is found scattered throughout the conglomerate,
locally replacing organic debris. Oswaldpeetersite occurs, associated with gypsum, along bedding planes ofa layer of siltstones within the conglomerate. Additional
associated minerals are cuprite, antlerite, goethite,
lepidocrocite, mbobomkulite, hydrombobomkulite,
sklodowskite and two undefined uranium minerals.

1685 39#6-déc-01-2290-13

1686

OPTICAL CHARACTERISTICS
Oswaldpeetersite is biaxial negative. The indices ofrefraction, measured at 589–599 nm, are  1.583(2), 1.669(2) and  1.712(2). The calculated 2V value is67.4(2)°. The optical orientation is Z || a, and the elongation is positive. Dispersion was not observed. Thepleochroism is X and Y very pale yellow to colorless,and Z pale yellow. Oswaldpeetersite, like rutherfordine,
does not fluoresce under 360 nm light; this contrasts
with joliotite, which strongly fluoresces, and withblatonite, which strongly fluoresces greenish yellow inultraviolet radiation.

X-RAY CRYSTALLOGRAPHY
Because of the small dimensions of the crystals, wewere unable to determine the crystal structure, the unit
cell and space group by single-crystal X-ray diffraction.
X-ray powder-diffraction data were recorded with aGuinier–Hägg camera using monochromatic CuK1 radiation ( 1.5406 Å). Silicon powder (SRM–640) wasused as an appropriate internal standard. Relative intensities of the diffraction lines were measured with an LS–
20 line scanner (Key Instruments, Täby, Sweden). The
peak positions were determined by using the computer

21/12/01, 12:48

OSWALDPEETERSITE, A NEW BASIC URANYL CARBONATE MINERAL

1687aAb
BFIG. 1. A. SEM photomicrograph of a radiating group of oswaldpeetersite crystals. Scalebar: 50 m. B. Closeup of A showing striations and morphology. Scale bar: 10 m.

program SCANPI (Johansson et al. 1980). The X-raydiffraction spectrum shows 56 diffraction peaks, whichwere indexed by the program TREOR (Werner et al.
1985). Indexing converged to monoclinic symmetry andthe unique space-group P21/c. The unit-cell parameters,
refined by the least-squares program PIRUM (Werner1969), are: a 4.1425(6), b 14.098(3), c 18.374(5) Å, 103.62(1)°, a:b:c = 0.2938:1:1.3033, V = 1042.8(3) Å3,1685 39#6-déc-01-2290-13

1687

Z = 4. The figure of merit values are M(20) = 10, F(20)= 17(0.018752,65). A fully indexed powder-diffraction
pattern is given in Table 1.

CHEMICAL COMPOSITION
Crystals of oswaldpeetersite were chemically analyzed with a Cameca SX–50 electron microprobe. An

21/12/01, 12:48

1688

THE CANADIAN MINERALOGIST

energy-dispersion scan indicated no elements with Zgreater than 8, other than uranium. Quantitative analyses were performed at 10 points using a beam size of 2
m, an operating voltage of 15 kV, and a beam currentof 20 nA. Synthetic UO2 was used as the standard. TheFIG. 2.

1685 39#6-déc-01-2290-13

mean content of UO3 is 81.47 wt.% (range 76.72 –84.21%). The H2O content was determined with athermogravimetric analyzer (TGA 2950, TA Instruments). The heating rate was 5º/min, with a constantflow of N2 at 50 mL/min. The combined loss of H2O
and OH is complete at 170°C and corresponds to a H2O
content of 12.30 wt.%. The content of CO2, calculatedby difference, is 6.23 wt.%. The oxide formula, calculated on the basis of 13 atoms of oxygen, is 2.03
UO3•1.01 CO2•4.88 H2O. The empirical formula, taking into account electroneutrality, is (UO2)2.03(CO3)1.01(OH)2.05•3.85 H2O. The ideal formula is (UO2)2CO3(OH)2•4H2O. Calculations of the Gladstone–Dale relationship, made using the constants of Mandarino (1981),
yielded a compatibility index of 0.0470 for the empirical formula and 0.0428 for the ideal formula, indicativeof good agreement between the physical and chemicaldata.

Fourier-transform infrared spectrum of oswaldpeetersite.

1688

21/12/01, 12:48

OSWALDPEETERSITE, A NEW BASIC URANYL CARBONATE MINERAL1689

INFRARED SPECTROSCOPYREFERENCES

The infrared spectrum was recorded by using theKBr dispersion technique (1 mg sample in 300 mg KBr)
with a Bruker Vector 22 Fourier-transform infrared
spectrometer over the range 400–4000 cm–1. The infrared-absorption spectrum is shown in Figure 2. The assignments of absorption bands are summarized inTable 2.

BOTTO, I.L., GARCIA, A.C. & DELIENS, M. (1989): Thermal andIR spectroscopic characterization of kamotoite. Collect.
Czech. Chem. Commun. 54, 1263-1268.

FORMATION AND STABILITY
Cjeka & Urbanec (1988) stated that in synthesis experiments in the system UO3–CO2–H2O, the phases
UO2CO3•nH2O and UO2(CO3)1–x(OH)2x•nH2O (n ≥ 0)
were characterized. In aqueous solutions, below a pHof 5, the dominant species is UO22+ in the presence ofminor quantities of (UO2)2(OH)22+, UO2OH+ and fractions of (UO2)3(OH)5+ and (UO2)4(OH)7+. At highervalues of pH, the uranyl ion hydrolyzes and forms a
number of polymeric hydroxide complexes according
the reactionx UO22+ + y H2O → (UO2)x(OH)y(2x–y) + y H+.
At a pH between 4.8 and 6.4, (UO2)2(OH)5+ is the dominant cationic species. In the presence of CO2, anionicuranyl hydroxyl carbonate and uranyl carbonate species
will be formed. At a pH between 6.5 and 8, the anioniccomplex (UO)2CO3(OH)3– is dominant (Burns & Finch1999). As a consequence, the following reaction can beconsidered at a pH between 6 and 7:(UO2)2CO3(OH)3– + (UO2)3(OH)5+ →(UO2)2CO3(OH)2 + 3 UO2(OH)2.
After hydration, the solid phase oswaldpeetersite can beexpected to form.

ACKNOWLEDGEMENTS
We are indebted to Ing. J. Jansens of the Laboratoryof Inorganic Chemistry, University of Antwerp forrecording the TGA curve, and to Dr. F. Fontan of theLaboratoire de Minéralogie, Université Paul Sabatier,Toulouse, France, for the electron-microprobe analyses.
We thank Dr. J.D. Grice and anonymous members ofthe Commission on New Minerals and Mineral Names,IMA, for their valuable comments. We also thank thereferees, Robert Finch and Andrew C. Roberts, Associate Editor Peter C. Burns and Robert F. Martin for
critical reading and comments that improved the clarityof this paper.

1685 39#6-déc-01-2290-13

1689

BURNS, P.C. & FINCH, R., eds. (1999): Uranium: Mineralogy,
Geochemistry and the Environment. Rev. Mineral. 38.
CEJKA, J., SEJKORA, J., MRÁZEK, Z., URBANEC, Z. & JARCHOVSKY,T. (1996): Jáchymovite (UO2)8(SO4)(OH)14•13H2O, a newuranyl mineral from Jáchymov, the Krusné Hory Mts.,
Czech Republic and its comparison with uranopilite. Neues
Jahrb. Mineral., Abh. 170, 155-170.
________ & URBANEC, Z. (1998): Contribution to the hydrothermal origin of rutherfordine, UO 2 CO 3 . Casopis,Národního muzea rada prírodovedná 157, 1-10.
DELIENS, M. & PIRET, P. (1991): La haynesite, sélénite hydraté
d’uranyle, nouvelle espèce minérale de la mine Repete,
comté de San Juan, Utah. Can. Mineral. 29, 561-564.
FARMER, V.C. (1974): The Infrared Spectra Of Minerals.
Monograph 4, Mineralogical Society, London. U.K.
JOHANSSON, K.E., PALM, T. & WERNER, P.-E. (1980): An automatic microdensitometer for X-ray powder diffraction photographs. J. Phys. E: Sci. Instrum. 13, 1289-1291.
MANDARINO, J.A. (1981): The Gladstone–Dale relationship.
IV. The compatibility concept and its application. Can.
Mineral. 19, 441-450.
M ARCKWALD , W. (1906): Über Uranerze aus DeutschOstafrika. Zentralbl. Mineral,, 761-763.
NAKAMOTO, K. (1963): Infrared Spectra of Inorganic andCoordination Compounds. John Wiley and Sons, New
York, N.Y.
VOCHTEN, R. & DELIENS, M. (1998): Blatonite, UO2CO3•H2O,a new uranyl carbonate monohydrate from San JuanCounty, Utah. Can. Mineral. 36, 1077-1081.
WALENTA, K. (1976): Widenmannit und Joliotit, zwei neue
Uranylkarbonatmineralien aus den Schwarzwald. Schweiz.
Mineral. Petrogr. Mitt. 56, 167-185.
WERNER, P.-E. (1969): A Fortran program for least-squares
refinement of crystal-structure cell dimensions. Arkiv.
Kemi 31, 513-516.
________, ERIKSSON, L. & WESTDAHL, M. (1985): TREOR, asemi-exhaustive trial-error powder indexing program forall symmetries. J. Appl. Crystallogr. 18, 367-370.
Received June 17, 2001, revised manuscript accepted
November 10, 2001.

21/12/01, 12:48