American Mineralogist, Volume 68, pages 456458, 1983

Metastudtite, UOa . 2H2O, a new from ,Shaba, Zaire

Mtcuel Delrr,Ns Ddpartement de G4ologie et de Mindralogie du Mus€e royal de I'Afrique centrale, B 1980 Tervuren, Belgium .arNoPeul PInBr Laboratoire de Chimie physique et de Cristallographie de l'Universfte, B 1348 Louvain-la-Neuve, Belgium

Abstract

Metastudtite occurs at the Shinkolobwe deposit in Shaba, Zaire.lt appearsas aggregatesof flexible pale yellow fibers. Electron microprobe analysis gave UOa 88.1%. H2O by TGA- l0%. Formula UOa 'zHzO. Powder data are similar to those of the synthetic compoundand to those of heatedstudtite (UOa : 4H2O).Orthorhombic, probable spacegrouplmmm,a:6.51(l),b=8.78(2),c=4.21(l)4.,2=2,d(caIc.):4.67mglcm3. Strongestlines in the X-ray powder pattern are 5.22 (l00xll0), 3.54 (S0) (l0l), 4.38 (50X020)and3.79 (50X0ll). Themineralisopticallybiaxialpositive. y-- 1.760(parallelto c, fiber axis), p = 1.658and a: 1.640.Metastudtite is associatedwith uranophane, kasolite and hydrated uraniumJead oxides. Metastudtite is compared with studtite and lepersonnite.

Introduction about twenty samplesfrom Shinkolobwe regarded Two hydratesofuranium peroxidecan be synthe- as studtites in several mineralogical collections. sized: UOa . 4H2O (below 50"C) and UO4 . 2H2O Our work indicates the existence of at least 3 (above70'C). Both hydratescoexist between 50 and different fibrous qualified with the name 70'C (Sato, 1961a).A study by thermal decomposi- "studtite" in that deposit: tion (Sato, 1961b)shows that the formulaeadopted Studtite above are preferable to UO3 .H2O2' 3H2O and UO3 . H2O2 . HzO. X-ray powder patterns of both About 12 samples effectively correspond to the compoundshave beenpublished by Debets(1963). original species described by Vaes in 1947. Their Vaes (1947)reported the original studtitediscov- properties are identical to those of the Menzen- ered at Shinkolobwe (Shaba,Zaire) to be a hydrated schwandstudtite. Their chemicalcomposition cor- uranium carbonate as the result of a qualitative responds to that given by Walenta (1974): chemical analysis. Studying fibers of the same UO4'4H2O. This confirmsthat Vaes and Walenta appearance,found at Menzenschwand(Black For- worked on fibers of the same nature and that Vaes est, WesternGermany), Walenta (1974) determined probably performed his chemical test (release of them, by their optical properties and X-ray powder COz by reaction with HCI) either on an impure pattern, to be identical to the studtite from Shaba material or on fibers belonging to another species. and to the synthetic compound UO4 . 4HzO.Chem- ical tests confirmed the composition as that of an Lepersonnite oxide (probably a peroxide) and not of a carbonate. Six samplesconstitute a new mineral speciesof Walenta also studied the thermal behavior of stud- which the chemicalcomposition and physicalprop- tite. By heating above 60oC, he obtained erties are distinct from those of studtite. This new UO4.2H2O. As the dehydrationwas irreversible, mineralis a hydrous uranium, calcium, silicon and he suggestedthe possibility of the natural occur- rare earth carbonate whose ideal empirical formula renceof this species. is: CaO ' (RE)zOr. 24UO3. SCO2. 4SiO2. 60H2O. Since the investigation of Walenta was performed It has been described under the name of leperson- on a sample which was different from the original nite by Deliens and Piret (1982).Vaes may have Shinkolobwe material. we undertook the studv of performed his test on fibers of this species; leper- 0003-004x/83/0304-u56$02.00 456 DELIENS AND PIRET: METASTUDTITE sonnite and studtite have indeed been found to be nodules of kasolite and powdered yellow uranopi- closely associatedin the samplesstudied here. lite completethe association. Metastudtite Physical and optical proPerties Finally two sampleswere identified as being the The small amount of metastudtite available and compound UO4. 2H2O of which this is the first the minute diameter of individual fibers (-0.001 occurrenceas a naturalphase. A descriptionofthis mm) do not permit the determination of some mineral under the name of metastudtite is given physicalproperties such as cleavage,hardness and below. density.The streakis yellowishand the luster silky. Under the microscope, metastudtite appears as Occurrenceand associations pale yellow fibers or elongated tablets. No pleoch- Metastudtite has been found in two samplesfrom roism was observed.The mineralis biaxial positive Shinkolobwe (Shaba, Zaire) preservedin the miner- with refractive indices 7 : 1.76010.002,I : alogical collection of the Musde royal de I'Afrique 1.658t0.002and a : 1.64010.002(2V calculated centrale. The first sample is a grey dolomitic rock, 47.7'). Z : c (direction of elongation).According to brecciatedand deeply altered. The surfaceis almost Walenta (1974)the dihydrate has higher indices of completely covered with yellow and orange coat- refractionthan studtite(y: 1.680and e: 1.537)' ings in which the following minerals have been He provides only a : 1.758for metastudtite.This identified: grey fibers of ; prismatic agrees closely with the value for 7 determined in tablets of amber yellow becquerelite;red pseudo- this study. The mineral does not fluoresce under hexagonalcrystals of masuyite; red-orangeshort short or long wave ultraviolet light. crystalsof kasoliteand red microcrystalsof wolsen- dorfite. The latter crystals serve as support for two Chemical composition small radiatednodules of metastudtite.These nod- An electron microprobe analysis was performed ules are pale yellow and have a diameter of about in the Centre d'Analyse par Microsonde des Sci- 1.2 mm. The secondsample is a massiveblock of encesde la Terre (cnrrasr)(Laboratory of Petrogra- purple black uraninite. One face is coveredwith a phy of the University of Louvain, Belgium,analyst: thick yellow coating. It is mainly composed of J. Wautier). Low potential was used in order to needlesof uranophane,which form rounded struc- avoid the destructionof the needles.Usual correc- tures, and short crystals of soddyite. A few aggre- tions were applied by the mean of a zAF program. gates of flexible and silky fibers of metastudtite are Using metallic uranium as the standard,the meanof mixed with uranophane(Fig. 1). The fibers are pale 3 analysesgave UO3 83.4% or UO+ 88.1%o.TGA yellow and up to 3 mm in length. A few orange analysison a 0.5 mg samplegave -lDVo water. This value is regarded as approximate because of the small samplesize. The ideal formula UO4'zHzO requiresIJO4 89.3%and H2O 10.7%. Metastudtite is soluble without effervescencein hot HCl. X-ray data The X-ray powder data (Table l) show the identi- ty between metastudtite and the synthetic com- pound UO4'2H2O (Debets, 1963 and Walenta, 1974).Two additionallines at 7.25 and3.l8A corre- spond to the strongest lines of hydrated uranium- lead oxides such as fourmarierite. This latter com- pound occupies the fiber core of some fibers of metastudtite where it appears as a reddish thread. A similar associationhas been observed in some. studtites. Yellow studtite fibers with reddish fiber Fig. l. Scanning electron photomicrograph of fibrous core have been heated to 100'C for 2 hours. The X- metastudtite(left) and tabular uranophane(right). ray powder pattern of heated material shows the 458 DELIENS AND PIRET: METASTUDTITE

Table L X-ray powder patterns for natural metastudtite, powder data does not differ significantly from the ' synthetic UO4 2H2O and heated studtite values given by Walenta (1974). Therefore these latter valueshave beenadopted here: a : 6.51(l), b lbtslLdtlte Ent]€tic Heated Etral. studtlte Shtulko1ob€ U34,.2 Hro : 8.78(2),c : 4.21(l)A,Z:2, calculateddensity : PEst Etdy Debets,l953 I'IaLsta,I974 prest shdv 4.67 mglcm3Orthorhombic, probable space group hkl alc do I/Io d,o I/7o do I/Io do Immm (Debets, 1963).Single crystal ^studiesgave i.25i 5ob 6.21'' 30 only the valuesof the c axis: 4.2-+0.14. rro 5.23 5.22 roo 5.23 loo s,24 rO 5.23 roo o204,39 4.38 50 4.39 33 4.4L 1 4.394 50 Nomenclatureand conservation 3. 985" 20 The name metastudtite was chosen for the new oll 3.795 3.'t9 50 3 .80 33 3.80 7 3.798 40 ror 3.535 3.538 80 3 .53 34 3. 54 I 3. 534 70 mineral because it is a dehydration product of 3. 378" 20 studtite. The mineral and name have been approved 200 3,255 3.214, 3.25 I 5 J.ao o J.z)J zu 3.r80' 5Ob by the Commission on New Minerals and Mineral 3.r52:: 30 3.075rr 20 Names, IMA. r2r 2.753 2.756 30 2.75 2r 2.75 5 2.'753 30 The type specimenof metastudtiteis preservedin 130 2.669 2.669 zw z.oo I zL 2.67 5 2.667 30 the mineralogical collection of the Mus6e royal de 220 2.6L5 2.611 9 2.5r 3 2.615 5 ++ I'Afrique centrale (Tervuren, Belgium) under the z.alz, ) 2.536rr 5 number RGM 13748.There exists a cotype RGM 2rr 2,47L 2.46't 20 2.469 19 2.47 5 2.468 25 13755in the samecollection. o3r 2.403 2.398 20 2.402 15 2.40 4 2.406 20 o40 2.195 2.191 5 2.193 5 2.19 2 2.199 5 3ro 2. lo7 References 2.ro3 ]s 2.1os 12 2. ro 5 2.ro2 20 ooi i.ios Debets, P. C. (1963)X-ray diffraction data on hydrated uranium rr2 r.953 r.950 15 r.953 13 r.955 4 I.954 20 peroxide. Journal of Inorganic and Nuclear Chemistry, 25, 23r r,933 r.928 15 r,932 r3 r.927 5 r.93r 20 727-:t30. 30r r.929 r.926 I Deliens, Michel and Piret, Paul (19E2)Deux nouveaux mindraux o22 L .898 r .8 98 5 de Shinkolobwe: la r4r r.855 r.859 ro r.863 13 r ,852 3 r .860 5b bijvoetite et la lepersonnite, carbonates 240 r.420 r.8r5 3 1.818 4 r.8r9 r r.807 3 hydrat€s d'uranium et de terres rares. CanadianMineralogist, 202 L.'158 r.'t6-1 ro 1-'167 6 r.768 4 t.77L 15 in press. Sato, Taishi (l96la) Uranium peroxide hydrates. Naturwissen- + 24 lires + 24 lilE + 6 llres schaften,48, 668. Pattepn obtaired ia 114.6mdia@ter c@tu usitg Cv Ib niekel-filtered. Sato, Taishi (l96lb) Thermal decompositionofuranium peroxide X-"4di/tion. Intensitie s e etircted oi'MLLA ( p@sent etudA ) b = bwd Lire Hydrates. Naturwissenschaften,48, 693. = + Line of, hAdruted. U-Pb otide erch ds fowwiepite ll = Liie of cwite. Vaes, J. F. (1947)Six nouveaux min€raux d'urane provenant de Shinkolobwe (Katanga). Annales de la Socidt€ g6ologiquede Belgique,70,212-225. associationof the major metastudtite with curite, a Walenta, Kurt (1974)On studtite and its composition. American hydrated uraniumJeadoxide (lines at 6.27,3.985, Mineralogist, 59, 166-17l. 3.378,3.152 and 3.075Aparticularly). Manuscript received,April 29, 19E2; The refinement of the cell constants using our acceptedfor publication, August 9, 1982.