673

The Canadian Mineralo gist Vol. 37, pp 673-6'78(1999)

STRONTIOMELANE, SrMn4*6Mn3*zOrs, A NEW MINERALSPECIES OF THE CRYPTOMELANEGROUP FROMST. MARCEL- PRABORNA,AOSTA VALLEY, ITALY

NICOLAS MEISSER'K

Musdede gdologieet Institutde mindralogie,BFSH-2, Universitd, CH-1015 Lausanne, Switzerland

ELENA-ADRIANA PERSEIL

Laboratoirede mindralogie,Musdum National d'Histoire Naturelle, 61, rue de Buffon,F-75005 Paris, France

JOEL BRUCCER$

Mineralogischund Petrographisches Institut, Universitiit, Bernoullistasse 30, CH-4056BaseL, Switzerland

PIERRE-JACQUES CHIAPPERO

Galerie de mindralogie, Mus6um National d'Histoire Naturelle, 36, rue Geoffroy-Saint-Hilaire, F-75005 Paris Cedex, France

Assrnncr

Strontiomelane is a new mineral speciesfrom the Praboma mine near Saint-Marcel, Aosta Valley, Italian Alps It occurs as small anhedral inclusions (about 100-200 pm) and veinlets associatedwith braunite, cryptomelane, hollandite, quaftz, fluorapa- iite, titanite,jadeite and strontiopiemontite. The new speciesis opaque, black with a submetallic luster and a strong grey-white pleochroism; in plane-polarized light in oil immersion, it presents a medium anisotropy with grey-blue to white tints. Strontiomelane, whose ideal formula is SrMn4+6Mn3+2O16,crystallizes in space group P21ln (14) with a 10.00(1), b 5.158(1), c 9.83(1) A, p 90.64(6)' andZ = 2. The srrongesrlines in the X-ray powder pauern td in A(D(htl)l are: 3.15(100)(103), 3.13(80)(103),2.409(80)(122),2.17060)(320)and1.556(50;i225)Thecalculateddensityis466(1)g.cm3.Strontiomelaneis the Sr end-member of the cryptomelane group The proposed name is derived from the chemical element strontium and the color black, melas,- anos in Greek.

Keywords: strontiomelane, strontium, manganeseoxide, cryptomelane group, Praborna,Alps, Italy.

Souvatne

La strontiom6lane est une nouvelle espdcemin6rale d6couverte d la mine de Praborna,prbs de Saint-Marcel, vall6e d'Aoste dans les Alpes italiennes. Cette espdcese prdsenteen petites inclusions x6nomorphes de 100-200 pm ainsi qu'en veinules. Les min6raux associdsh la strontiom6lane sont: la braunite, la cr1ptom6lane, la hollandite, la fluorapatite, la titanite, le quartz, la jad6ite et la strontiopi6montite. La strontiom6lane est noire, opaque, avec un 6clat subm6tallique et un fort pldochrolsme gris blanc; en nicols crois6s, elle pr6sente une anisotropie d'intensit6 moyenne avec des teintes gris bleudtre d blanc. La formule chimique iddale de la strontiomd^laneest SrMna+6Mn3*2O16.Cette espdcecristallise dans le groupe d'espace P21ln (14) avec a 10.00(1),b 5.758(7),c 9.88(1) A. P 90.64(6)' et Z =2. Les raies principalesdu diagrammede poudre [d en A(IXftLl)] sonr: 3.15(100)(103),3 13(80X103),2.409(80)022),2t70(60)(320) et 1.556(50X225).La densitdcalcul6e est de 466(1). La strontiom6lane est le terme sfontifdre du groupe de la cryptom6lane. L'6tymologie du nom d6rive de l'6l6ment strontium et du grecmelas,- anos. signifiant noir.

Mots-cl6s: strontiom6lane, strontium, oxyde de mangandse,groupe de la cryptom6lane, Praboma, Alpes, Italie

a E-mail address: [email protected] $ Present address:Off,rce 258, VIEPS, Department of Earth Sciences,Monash University, Clayton, Victoria 3168, Australia. 674 THE CANADIAN MINERALOGIST

INrnooucrroN contentup to 1.54 wt.Vo;T = 350'C, P < 7 kbar); Cabella et al.1994). Cryptomelane - hollandite-type compounds are tet- Preliminary studies of the ore from the Praborna ragonal or monoclinic (pseudotetragonal)complex mine by electron microprobe has suggestedthe emer- oxides, of general formula A1BgO16.nH2O(0 < x < 2, gence of a new Sr end-member in the cryptomelane 0 < n < 0.16) (Bums & Burns 1979,Kudo et al. 1990, group, associatedwith strontiopiemontite in the same Waychunas1991). Only memberswithA = Ba, K, Na, sample (Perseil 1988). The mineral is named strontio- Pb, Sr and B = Cf+, Fe3*, Mg, Mn4*, Ti, V3*, Zn, Zr melane,from the element strontium and from the Greek (Perseil 1988, 1990, Fleischer & Mandarino 1995) are melas,- anos,black. The new specieswas approved by actually known as mineral species. In this paper, we the Commission on New Minerals and Mineral Names describe the properties of a newly establishedmember of the International Mineralogical Association prior to of the series,strontiomelane, discovered at the Praborna publication. The holotype material is deposited at the mine, in Aosta Valley, Italian Alps. Geological Museum of Lausanne, Switzerland (#MGL 58770). Cotype material is also preserved at the BacrcnouNo h{ponlrerroNr Laboratoire et Galerie de Mindralogie, Mus6um National d'Histoire Naturelle, Paris, France (#SM Natural examples of this solid-solution series are 7090.96). typically manganian (ideally with B = Mna*): crypto- melane (A = K), hollandite sensu stricto (A = Ba), OccunruNcs manjiroite (A = Na) and coronadite (A = Pb). Small amounts of Ce, La, Nd, Y, P and Nb have also been The Praborna manganesedeposit is situated about observedby Fodor et al. (1994) and Mitchell & Meyer 5 km south of the village of Saint-Marcel, in a lateral (1989) in natural hollandites. An ever wider variety of valley of Val d'Aosta, Italy. Manganese-enrichedhori- synthetic phaseswith the hollandite-type structurehave zons are embeddedin a 4- to 8-m thick quartzitic layer been reported, with A = Li, Na, K, Rb, Cs, Mg, Ca, Sr, that representsthe basal part of the sedimentary cover Ba, Ag, Tl and Pb, andB = Sc, Ti, Cr, Mn4*, Fe, Co, Ni, of an ophiolitic sequence, tectonically related to the Cu, Zn, A1, Ga, In, Si, Ge, and Sn, defining 30 end- Piemont Nappe. During the Alpine orogenesis,this ore member compositions (Pentinghaus 1978, Zhang & concentrationwas metamorphosedin the eclogite facies Burnham 1994). in Cretaceous times and then retrograded to the In the group of manganianphases, the crystal struc- greenschist facies in Tertiary times (Mottana 1986). ture of pure synthetic hollandite, BaMn6O16,was first During the late stages of the polyphase Alpine meta- studied by Bystrcim & Bystrdm (1950): large cations, morphism, in the greenschistfacies, the manganese-rich like Ba, occupy the A site within the tunnel formed by horizons were subsequently cross-cut by networks of corner-sharing of columns of edge-sharing (Mna+O6) veins and late fractures responsiblefor the mobilization octahedra along [001]. These authors showed that the of severalelements like K, Ba, Sr, Sb, W and As (Mar- ideal structure possessesa tetragonal symmetry, I4/m. tin-Yernizzi 1982, Mottana & Griffin 1986, Perseil Two monoclinic structuresarerecognized in this group: 1985, 1988, 1991,Perseil & Smith 1995).Strontio- Mukherjee (1960) found evidenceof a monoclinic sym- melane crystallized during this late stage of veining. metry, space grotryP21ln, for natural ferrian hollandite, The mineralogical association of Praborna, with a BaFeMn7Ol6, and Miura (1987) investigated a natural long and complex metamorphic story, has already pro- potassium- and iron-rich hollandite from India and duced two new mineral species:piemontite, a manga- found a monoclinic structure,I2lm.ln contrast with the neseend-member of the epidote group (Kenngott I 853) observationsof Bystnim & Bystrrim (1950), Mukherjee and rom6ite, a calcium-antimony oxide, structurally (1960), Post et al. (1982) and Mrtra et al. (1987) re- relatedto pyrochlore(Damour 1841,Brugger et al.1991). ported that with increasingBa2+ content, with respectto K*, the symmetry of cryptomelane changes from tet- Hesrr aNo PanacsNpsrs ragonal to monoclinic. For several years, significant amounts of Sr have Strontiomelane occurs as thin (100-200 pm), sub- been found in minerals of this group. Occurrences of metallic, black, elongate xenomorphic inclusions com- Sr-bearing hollandite have been reported in several monly aggregated with braunite in quartz and, more localities: 1) the Falotta and Parsettens mines, rarely, in violet pyroxene (variety "violan" of diopside- Oberhalbstein, Graubiinden, Switzerland, as a super- aegirine-jadeite) and in strontiopiemontite. Thin late- gene mineral (with 24 wt.% SrO) resulting from the stage veinlets of the new species were also observed oxidation of Sr-bearing sursassiteand barite (Perseil associatedwith braunite, hollandite, cryptomelane,ja- l99O),2) the Cerchiara mine, eastern Liguria, Italy deite, strontiopiemontite, Sb-bearing titanite, As-bear- (1.93-3.72 wt.VoSrO;' 250 < T < 300'C, 2 < P < 3 kbar), ing fluorapatite and quafiz. On polished surfaces, (Cabella et al.1994), and 3) the Upper Jurassicquartz- strontiomelanediffers slightly from braunite by a lower itic meta-arenitesof the Maritime Alps, Italy (SrO hardnessand a poorer polish. STRONTIOMELANE FROM THE PRABORNA MINE. ITALY 675

TABLE I REFI.ECTANCE VAIIJES OF STRONTIOMELANE of hollandite; between crossedpolars, its anisotropy is moderate,with a grey-blue to white tint. No internal re- Refl€ctil@ Reflectance Wavelengths flections are noted, and the color of the streak is sepia. |]lamm nmum (coM) Reflectance values of the new speciesare presented [R%w] tR%minl [l,m] in Table l. The observed values of reflectivity of strontiomelane lie in the range of hollandite and 342 260 4',70 317 244 543 cryptomelane (Perseil & Pinet 1976, Picot & Johan 306 ,14 547 1982). )o1 223 657 The Vickers hardness,measured by micro-indenta- tion using a load of 100 g, gives a mean of 398 and a Objtrtive: LEITZ 50/0 85; stedtrd LEITZ WTiC; meeued in air range of 309-450 (number of measurements:16). Strontiomelane is brittle, with a rarely observed cleav- age. The size of the new mineral precluded a direct mea- Pnystcal Pnoppnrres surementof the density. It was calculatedfrom the com- position richest in Sr (Table 2, #6) and the refined In polished sections, microscopically, strontio- unit-cell parameters:4.66( | | g.cm-3. melane is an opaque mineral. Observed in oil immer- sion, in plane-polarized reflected light, the mineral is X-ray-dffiaction study grey with a strong grey-white pleochroism similar to that As all the available grains of the new mineral spe- cies are quite small, the crystallographicstudy was made X-ray-diffraction data and ana- TABLE 2 CIIEMICAL COMPOSITIONOF STRONTIOMELANE, with a Gandolfr camera. ST MARCEL - PRABORNA AOSTA VALLEY. ITALY lytical conditions are presentedin Table 3. Comoared with the ionic radius of Ba2* and K+. that of Sr2* is smaller. Its presence as an occupant of the tunnel in the structure produces a collapse of distorted

MrO, wt% 60 36 59 E3 59 E7 6t 99 5993 5E71 walls of octahedra, which reduces the symmetry to M&O3 lE t0 l8 67 1879 1286 168l 165l monoclinic (Zhang & Burnham 1994). The powder pat- Ferq 245 244 251 62'7 5 24 627 tern of strontiomelanewas successfully indexed with a Tio, 046 049 0 45 20'l 0 53 070 CoO 001 008 oo2 0 t4 000 000 cell of monoclinic symmetry. The refined unit-cell pa- CUO 000 000 000 000 000 000 rameters, calculated by a least-squaresmethod, are: a MO 000 001 000 000 000 000 sio, 0 t8 037 023 0 14 045 045 10.00(1),b 5;758(7),c9.88(1) A, B 90.64(6)",vs68.8s KrO 742 144 150 059 089 083 43. a/b = 7.736:c/b = 1.715 andZ = 2. NarO 017 011 020 027 008 017 powder Pbo 000 000 000 000 000 000 That some peaks are lacking in the diagram CaO 014 ol4 014 000 000 000 suggestsspace group P2 tln (14). Moreover, the unit cell BaO 395 310 327 282 173 139 calculated with space grotp I2/m (12) does not agree sro 915 944 956 964 t2 t5 127'l 2 9709 9672 96 56 9679 97 81 97 80

Structwal fomulre* Mo* qJo 571 568 s69 579 562 552 TABLE 3 X- RAY POWDER-DIFFRACTIONDATA Mn* 196 195 t9'7 | 32 t'73 | 71 FOR STRONTIOMELANE FROM PRABORNA ITALY 025 025 026 064 053 064 Ti 005 005 005 021 005 007 Cu 000 000 000 002 000 000 I* dd hkl I* dou hkl Co 000 001 000 000 000 000 N 000 000 000 000 000 000 'to2 si 003 006 003 oo2 007 0 06 l0 702 tol t0 1997 1994 322 t E00 800 800 800 800 800 30 496 495 002 5 t9E2 I 993 322 30 352 352 2ll 5 1937 1940 105 K 025 025 026 010 015 014 30 350 351 202 30 lr55 1852 5ll Na 005 003 005 oo7 002 0 04 100 315 313 103 30 lE43 1844 124 Pb 000 000 000 000 000 000 80 313 3t3 103 >5 t112 1763 132 Ca 002 002 002 000 000 000 5 286 2 88 020 >5 1749 t'155 404 Ba o2l 020 018 015 009 007 30 275 2767 021 5 1702 1707 5 0 3 Sr 073 075 076 016 096 101 f 25(X 2496 220 20 l66E 1663 600 E 125 127 1,08 122 126 >5 2481 2473 004 20 l64E 1638 513 80 2409 2416 122 50 1 556 l s5l 22s 40 2.229 2226 402 20 1436 lMr 040 * The structwal fomulre re calculated on fie breis ofeight octahedrally @ordinated 30 2217 22t'l l 14 20 1369 1371 241 qtidB, whos @ncstratim ue quoted in qlt (atoms ps fomula unit) TheF dats 60 2170 2179 320 20 1355 1364 515 were acquired with a CAMEBAX elechon microuobe at the Mus6u National 20 I 303 I 301 3o7 d'Hstoire Natrrelle, Pais Opeating otrditios : 15 kV, l0 nA Stmdilds md X-ray lines ured for malysisr strontimite (Sda), buit€ (Barc), orthoclffi (KKo), albhe (NaKc), rutile (TiKa), rhodonite (MnKa), hffitite (Fdo), Co metal (Co,(c), Cu Gmdolfi rusa, I 14 6 m h dimeter FeKd Mn-filtered radiatio4 40 kV, 20 mA m*al (Cu,(c), Ni metal $i]rc), galw @M.1B) md wollastonite (Si.

with the observed d values. Certain weak lines cannot be indexed in this spacegroup.

CHsvrcnl CorraposruoNalo DrscussroN

Back-scatteredelecfron images obtained by scanning electron microscopy show the distribution of Sr in the crystal (Figs. 1, 2). These images have been used to choose the areas most enriched in Sr, to be analyzed with the electron microprobe. The results of selected analyses are presentedin Table 2. Considering all the microprobe results,the crystalsalso display zonesof Ba- rich (hollandite) to (K+Na)-rich (cryptomelane) com- position. According to Bystrcim & Bystrcim (1950), Fleischer(1964) and Bums & Burns (1979),the sffuc- tural formulae of hollandite and cryptomelane are re- calculatedon the basis of 16 atoms of oxygen, implying some Mn as Mn3* instead of Mn4* in order to account for charge balance. In recalculating the data, we have assumedthat Sr entersthe channel site, as do Ba, K and Frc. I Back-scatteredSEM imageof strontiomelanefrom Na, and we have estimatedthe ratio Mn3+A{n4+on the Praborna.Scale bar: 100pm basis of the relationshio Mn3* + Mn4* + Fe3++ Ti4+ + sia++ co2+ + cu2+ + Ni2* = 8. With this calculation, all the strontiomelane compo- implies, among other substitutions, the following set sitions are compatible with the formula (Sr,K,Ba)r z: starting from ct-MnO2 (or, more conveniently, (Mn;Fe,Ti)sO1 and, ideally, SrMn4*6Mn3*2O16.Thrs 6 IMna*sO16):

Frc. 2. Back-scatteredSEM image and X-ray images of Sr (Ict), K (rKa) and Ba (lct) in Ba- and K-rich strontiomelane from Praborna Scale bar: 10 um STRONTIOMELANE FROM THE PRABORNA MINE. ITALY 677

n Mn4* - (Na, K) Mn3+ cryptomelane series,and Post et al. (1982) have investigated the role of Ti4* in the octahedralsite. The Fe3+- (Mn4++ Mn3i) n 2Mna* = Ba 2Mn3* hollandite - Tia* diagram (Fig. 3b) shows a significant replace- ment of Mn by the other two cations. Moreover, inter- n 2Mn4* = Sr 2Mn'* strontiomelane mediate Ba-rich members of the priderite series(Ba, K, Sr)1-2Qi,Fe, Mn)sO16have been describedby Perseil hence the choice of a plot in terms of 2(Na + K) - Sr - (1991), suggestingthat a solution between priderite and Ba in Figure 3a. This diagram shows that there is a con- hollandite - cryptomelane - strontiomelane exists at tinuous solid-solution between hollandite and crypto- Praborna. melane and between cryptomelane and strontiomelane No H2O has been detectedby infrared (IR) spectros- in the analyzed crystal. It is less clear whether a com- copy (Nicolet 740 IR plan II microscope, scanbetween plete solution also exist between strontiomelane and 4000 and 2000 cm l). However, once the Mn3*:Mn4* hollandite. ratio has beencalculated using the above equation,sums Considering the octahedrally coordinated sites, Mn of weight percent oxide are low. The sum of oxides has is replaced by Fe3* and Ti4+, a feature already noticed a mean value of 96.2 considering all the analysesdone in the late paragenesesat Praborna (Perseil & Smith on the sample, and 96.7 for analysesof strontiomelane 1995).Bystrtim & Bystrom (1950)and Fleischer (1964) only. The standard deviation is 1.5 and, therefore, the have mentioned the substitution of Mna* by Al3* and sum ofoxide can be consideredto be signifrcantly lower Fe3* in the cryptomelane- hollandite solid-solution than 100. There are three hypotheses, all compatible with one another,to explain this feature: 1) there is some H2O in the channel, but its amount is below the detec- tion limit of the IR spectrometerapparatus used, 2) other large-size cations are present as trace elements in the structure and have not been detectedby electron micro- probe, and 3) microdefects at the surfaceofthe polished thin sectionspreclude accurateanalysis. Despite this problem, we consider that at least at Praborna. strontiomelane is the Sr end-member of a Strontiomelane solid solution involving cryptomelane and hollandite as the other two end-members.Either presentas inclusions or as veinlets. strontiomelane is related to late metaso- aaa matism involving Sr, but also Ba, K and Sb. Strontio- t- o product of alteration, but of a melane in Praboma is not a a hypogene origin, such as some hollandite-group phases 7:..' ao' o describedbyFleischer (1964). Othercations, e.9., Ag+, Cryptomelane Hollandite Tl+, Li+, cs+, Rb+,Mrg2*,ca2*,ce3*,La3*,Nd3+, sm3+, 2(K+Na) Ba(+Ca) Gd3+,Eu3+ and Dy3*, can enter the channelsof the iso- - (Pentinghaus (Mna + Mns) structuralseries cryptomelane hollandite 1978,Fodor et al. l994,Zhang & Burnham 1994)with correspondingnew end-members.This structural char- acteristic provides an insight in the searchof structural hosts in synroc (Ringwood et ctl. 1988) for the immobi- lization of radioelements(e.g., eoSr and l37Cs)rejected from nuclear fuel in the recoverv Drocess. rl Stronliomelane AcrNowleocsl\4pNts

We are greatly obliged to the metallurgical laborato- ries of the Federal Polytechnic School of Lausannefor the use of their microhardness apparatus. K. Schenk (Institut de cristallographie, Universit6 de Lausanne), Ph. Th6lin (Institut de min6ralogie, Universit6 de Lausanne)and M. Guiraud (Laboratoire de min6ralogie, Fe3* MNHN Paris) provided valuable suggestionsto improve the check-list for the new mineral proposal and helped FIc. 3. The composition of cryptomelane-groupminerals in revising the manuscript. Valuable comments on the from Praborna (95 data-points) in terms of the A- and B- manuscript were received from A. Mottana and an site occupancies(a and b, respectively). anonymous referee. 678 THE CANADIAN MINERALOGIST

RsFEnBNces Italy). In Crystal Chemistry of Minerals. Int. Mineral. Assoc , 13th Gen. Meeting (Vama), 635-640. BRUGGER,J., GrnnE,R., Gursen, S. & MsssBn, N. (1997): The crystal chemistry of rom6ite. Contrib. Mineral. Petrol. MurnBnlrp, A (1960): Space group and cell dimensions of a 127. t36-t46 specimen of hollandite. Acta Crystallogr 13, 164-165.

BuRNs,R.G. & BunNs, V.M. (1979): Manganeseoxides. In PENTTNGHAUs,H. (1978): Crystal chemistry of hollandite, Marine Minerals (R. Burns, ed.).Rev. Mineral.6, l-46 A*M(O,OH)16 $ = 2). Phys Chem' Minerals 3, 85-86.

BysrRoM, A. & Bvsrnorra,A. M. (1950): The crystal structure PERSEIL,E.A. (1985): Quelques caract6ristiquesdes facibs d of hollandite, the related manganeseoxide minerals and ct- oxydes de manganbse dans le gisement de St. Marcel - MnO2.Acta Crystallogr.3, 146-154 Praborna, Val d'Aoste, Itahe. Mineral. Deposita 20,271- 276. CABELLA,R., LuccHErrr, G. & Menescorrr, P (1994): Sr-rich hollandite and cryptomelane in the Fe-Mn oxide deposit of (1988): La prdsence de strontium dans les oxydes the Cerchiara mine (eastem Liguria, Italy). Int Mineral. mangan6silires du gisement de St Marcel - Praborna (Val Assoc.,l6th Gen.Meeting (Pisa),Abstr.,6I. d'Aoste, Itahe). Mineral. Deposita 23, 306-308.

Dlnoun, A. (1841): Sur la rom6ite, nouvelle espdcemin6rale (1990): Sur la pr6sence du strontium dans les de St Marcel, Pi6monl Ann. des Mines 20(3),247 . min6ralisations mangan6sifbresde Falotta et de Parsettens (Grisons-Suisse)- 6volution des paragenbses.Schweiz. Fr-rrscHrn, M. (1964): Manganese oxide minerals.Vlll. M ineral. P etro gr. M itt. 70, 315-320. Hollandite. Advancing frontiers in geology and geophys- ics,227-232. _(1991): La pr6sencede Sb-rutile dans les concentra- tions mangan6sifbres de St. Marcel - Praborna (Val & Muo.rnrNo, J A (1995): Glossary of Mineral d'Aoste, ltalie). Schweiz. Mineral. Petrogr. Mitt. 71,341- Speciesl995.The Mineralogical Record Inc., Tucson, Ari- 347. zona & PrNBr,M. (1976): Contribution d la connaissance FoDoR,R.V, JAcoBs,R.S. & Beunn, G.R. (1994):Hollandite des roman6chites et des cryptom6lanes - coronadites - in Hawaiian basalt: a relocation site for weathering-mobi- hollandites Traits essentielset paragendses.Contrib. Min- lized elements.Mineral Mag 58,589-596. eral Petrol 55. l9l-204.

KENNGorr, A. (1853): Das Mohs'sche Mineralsystem (8 vol., & Srranu.D C. (1995): Sb-rich titanite in the manqa- Vienna, Austria. nese concentrations at st. Marcel - Praborna, Aosta val- ley, Italy: petrography and crystal-chemistry. Mineral. Kuoo, H , Mlune, H. & Henrv,a.,Y. (1990): Tetragonal-mono- Ma7.59,717-734. clinic transformation of cryptomelane at high temperature. Prcor, P. & JoH.lN,Z. (1982): Atlas of Ore Minerals.B.R.G.M. Mineral "r.fi,50-63. Press.Orl6ans. France. MARTIN-VERNIZzT,S. (1982): La mine de Praborna (Val d'Aoste, Italie): une sdrie mangandsifire mdtamorphisde Posr, J.E., VoN DREELE,R.B. & Buspcr, P R. (1982): Sym- dans Iefaciis dclogite. Thdse de 3dme cycle, Univ. Pierre metry and cation displacements in hollandites: structure et Marie Curie. Paris. France refinements of hollandite, cryptomelane and prideite. Acta Crystallogr. 38, 1056-1065. Mnctrlr-, R H. & MsvBn, H.O.A. (1989): Niobian K-Ba-V titanates from micaceous kimberlite, Star mine, Orange RrNGwooD,A.E., KBssoN,S.E., Rmvr, K.D., LBvINs,D.M. & Free State, South Africa. Mineral. Mag. 53,451-456. Reruu, E.J (1988): Synroc. In Radioactive Waste Forms for the Future (W. Lutze & R.C. Ewing, eds.). North-Hol- Mnrn-q.,H (1987): The crystal structure of hollandite Mineral. land, Amsterdam, The Netherlands (233-334). J.13.397-398. WAycHr,'NAS,G.A. (1991): Crystal chemistry of oxides and _, BANERJEE,H., HARryA,Y., Dlscul'rl, S. &Rov, S. oxyhydroxides In Oxide Minera.ls: Petrologic and Mag- (1987): Hollandite and cryptomelane in the manganese netic Significance (D.H. Lindsley, ed.) Rev. Mineral.25, oxide deposits of the SausarGroup, India. Mineral. J. 13, 11-68. 424-433. ZslNc, J. & BURNHAM,C W (1994): Hollandite-type phases: MorraNe, A. (1986): Blueschist-facies metamorphism of geometric consideration of unit-cell size and symmetry. manganiferous cherts: a review of the alpine occurrences. Am. Mineral. 79, 168-174 Geol. Soc. Am-, Mem. 164,267-299.

& GnrnN, W.L. (1986): The crystal chemistry of Received January 17, 1997, revised manuscript accepted piemontite from the type-locality (St. Marcel, Val d'Aosta, January 27, 1999.