Benyacarite, a New Titanium.Bearing Phosphate

707

The Caa.dian M brcralo gist Vol. 35, pp.7M -712 (1997)

BENYACARITE,A NEW TITANIUM.BEARING PHOSPHATE MINERAL SPECIES FROM CERROBLANCO, ARGENTINA

FRANCESCODEMARTIN1 Dipanimewo d.i ChfunicaStnttturale e StereochimicaInarganica" Universitddegli Sttrdi,Via Venezian21, I-201j3 Milmo, haly

HEBEDINAGAY Departanento de Geologla, UniversidadNacional de C6rdaba,C6rdoba Argentinn

CARLO MARIA GRAMACCIOLI Dipartimenndi ScienzedellaTerrq Sezionz di Mineralogia" Universitddegli Smdi, vin Botticelli23, I-20133 Milnno, Italy

TULLIO PILATI CNR"Centro per tn Satdiodelle Relazionitra Stntttura e Reaxivith Chimbq via Golgi 19,I-20133 Mitarc, haly

ABSTRACT

The new phosphatemineral speciesbenyacarite, (t12O,K)2TiW(I)214Q)z(POq)q(O,D2:l4H2O, closely related to paulkerrite andmantienneite, but poorerin Mg and K andricher in Mn2+and Tizt+, occurs in granitic pepatites in Argentina(Ceno Blanco, Tanti, C6rdoba).It is associatedwith other phosphaGssuch as triplite, and fluorides such as pachnolite. The mineral is orthorhombic,biaxial (+), with 2V 60(3)",Xllb,Yll c, Zll a. Theindices of refractionarel. a 1.612(3),p 1.621(3)and y 1.649(3). The unit-cell parametersare: a 10.561(5),f ZO.SSS(A),c l?.516Q) 4., spasegrotp Pbca,Z = 4, Da= 2.37 g'cra. The strongest seven lines in the powder-diffractionpattern [d i\ (L)(mi(hkt)] are: 3.13(1@)(0M),6.26(100)(002), 10.29(90X020), 7.51(80X1ll),3.76(50)(222),5.16(40X040),and 3.96(4O)(212). Benyacarite contains layers perpendicular to [010]composed of two kinds of octahedra.On both sidesof theselayers, there are POa tetrahedra, with oneface approximatelyparallel to the layen. The cavitiesexisting within the network of octahedraand tetrahedra are occupiedby K+ and HzO molecules. 'maweevite', Keywords: phosphates,benyacarite, new mineral species,paulkerrite, mantienneite, CerroBlanco, Argentina.

Somrtenr

Nous d6crivonsici la benyacmite,(lf2O,K)2TtM(l)2M(2)2eOi4(O,F)Sl4H2O, nouvelle espBcemindrale dtroitement li6e a la paulkerriteet la mantienn6ite;par rapport a c€ux-ci, ce phosphateest appauwi en Mg et K et enrichi en Mn2+et Ti. Elle fait partie d'un assemblagede phosphates,dont la triplite, et de fluorures,dont la pachnolite,dans des massifs de pegmatitegranitique clansla r6gion de Cerro Blanco,Tanti, C6rdoba en Argentine.Elle est orthorhombique,biaxe positive, avecun angle2V 6gald 60(3)', et l'orientationXll b, Y ll c, Zll a.I-es indicesde r6fractionsont o 1.612(3),P 1.621(3)etl l.@9(3). Les paramdtres rdticulairessotrr a 10.561(5),b t0.585(8), c 12.516(2)A, groupe spaaalPbca, Z = 4, Dx= 2.37 g:cwa. Les septraies les plus intenses du specfie de diftaction X (m6thode des poudres) ld et (L)(nJ@ftI)l sont 3.13(100X004),6.26(100)(002), 10.29(90X020),7.51(80X111), 3.76(5qQn),5.16(40X040), et 3.96(N)QL2).Ia benyacaritecontient des couches perpendicu- laires h [010] faits de deux sortesd'octabdres. De part et d'aufie de cescouches se trouvent des tdtrabdres PO+, dont unedes faces est sensiblementparallble b cescouches. Les cavitfs form6€sau sein de cettetrame d'octadtlres et de t6traedrescontiennent des ions K+ et desmol&ules de HrO. (Traduit par la Rddaction)

Mots-cl6s: benyacarite,phosphates, nouvelle espdce mindrale, paulkerrite, mantienneite, "maweevite", Cerro Blanco, Argentine.

I E-mail address:demartin@ stinch.csmtbo.mi.cnrit 708

IN"IR.oDucnoN TABIT 1. UMT{ELL DATA FOR MINERAI,S RELATEDTO BENYACARITE In the year 1984, two new titanium-bearingphos- phateminerals, paulkerrite and mantienneite,were dis- Parlkdid I4mtimites Bml,mier "Mdr@fte"1 coveredalrnost simultaneously. Paulkerrite was found alAl 10.49(') 10.M(2' 10.561(t to52 ba4i 20J5(r3) 20330{.4) 20.585(8) 20.52 in the 7U7 Ranchgranitic pegmatite,Arizona @eacor c IAI 12.44(2) 123r42) '251q2) lL42 et al. 1984),together with other phosphatestypical of groq such rocks. A similar occlurence of this mineral at Spae Pbu Pbu Pbe Pnc{?) Bendada,Portugal, was also reported (Schnorrer- . Kdhler & Rewitzer 1991). Contrary to the case for So|!|m of data: Pw et al. (lgd/'), # F@lct eraL (1984), i D@atin st af Q93), { Kydryuhm& Robzd€savffikala(1991). paulkerrite, mantienneiteis not typical of pegmatites, but comesinstead from a sedimentar5rdeposit at Anloua Cameroun@ransolet et al. 1984). The crystal-chemicalanalogy between paulkerrite TABI.E2. CHEMCALCOMPOSMONOFMINERAI.S REI.AIED TO and mantienneitewas alreadypointed out at the time of BENYACARII4 (Il2O,t0rI!l4l)rM2XPOaXO,t').14H2o their discovery on the basis of the close similarity in Pdikmite' Mantimeiter Beqiaffiter lvlatvryits"t unit-cell data"space group, and chemicalcomposition (Iables 1, 2). Particularlyinteresting is the presenceof Na - 0.06 0.07 titanium, an elementrarely found in naturalphosphates. K About one year later, anotler titanium-bearing Fe 0.45'l o.+zl I phosphatewas observedfor the fust time by one of us ttl l& 0.02 r.es l.5o 2.00 r.lo l.e4 M(Dsit (H.D.G.) in a granitic pegmatiteat Cerro Blanco, near i,,,,| | I MC r.43 0.07 n* Tanti, C6rdoba,Argentin4 together with other phos- | | | phates and with speciesparticulady rich in fluorine, C€ I'l 0.05J 0.olJ ) such as fluellite and pachnolite. On the basis of the Al o.3ol r.arl o.r4l o.rrl similarity in powder-diffraction patlems, mineral tlre r.'' r.azr.ss o.rz r.re r.rs r.ss M(2)sire was recognizedto be isostructuralwith paulkerriteand I fz.oo fz.oo I ri o.reJ J o.soJ o.orJ mantienneite;chemical analysis showed, however, sipif- icant differences in composition, thereby suggesting the possibility of a new species.This mineral,for which Ti 1.00 1.00 1.00 1.00 the name proposed, bmyacartte is could be considered P 4.00 4.00 4.00 as the Mn2+-rich member of the paulkerrite group; unfortunately,the preliminary analyticaldata obtained F 0.50 - 0.80 by electron microprobe were affected by systematic . errorsdue to extensivedehydration ofthe sampleunder AtoEic proportiN @ b8€d m 4 dom of P. Sorc of ,letq Pw et ql (1984), # Fmlerelal (19&4), f Dmtin et aL (lD3), t KydryasboE & the electronbeam, and were consideredinsufficient for Robzd€scvmsksya(l9l). complete characterization.Moreover, the only single crystal then availablewas of poor quality, and no defi- nite conclusionabout the spacegroup could be drawn: the symmefiryseemed to be monoclinic (with a angle B (CNMMN) (proposal of 90.9') rather than orthorhombic as for paulkerrite New Mineralsand Mineral Names and mineral and mantienneite(Gay 1990). Therefore, in order to 95402) was approved.The was namedin confirm the statusof a new mineral species,an accurate honor of Maria AngelicaR. de BenyacarO. 1928),a crystal-structuredetermination using suitablemateriat researcherwith a long affiliation with the Comision was consideredto be essential.Furthermore no strucarre Nacionalde EnergiaAtomica BuenosAires, Argentina, mineralogical determinationshad beenperformed yet on any of these for her confribution to studies.The type minemls,and a definitebasis for establishingthe crystal- materialis depositedaf the MineralogicalMuseum of the chemicalrelationships among the membersof this group Departnentof EarthSciences, University of Milano. was needed.After severalattempts, a crystal fragment of good quality was selectedout of a considerable Occunnmlce ANDPanacsNEsrs numberof samplesof benyacarite,and the crystal strucflre was determinedand refined accuralely(Dlemafia et al. The Cerro Nlaass mining distict is located in tle 1993).Besides confirming the orthorhombicsymmetry, Sierra Grande of C6rdoba Province, Argentin4 near spacegroup PDca,consistent with that of paulkerrite the locality of Tanti (on the RouteN. 20), 45 km west and mantienneite,the new refined data permitted a of C6rdoba(Frg. l). Bedrock in the district includesa consistentinterpretation of the results of the chemical group of granitic pegmatitesrelated to a pink monzo- analysis.Consequently, our proposalof benyacariteas granite of the Achala bathotth. The age of batholith a new specieswas submittedto the IMA Commissionon emplacementis Silurian @b/Sr, 399 X25 Ma: Rapela BENYACARITE. A Ti-BEARING PHOSPHATE 709

FALDA

COSQUIN

CORDOBA

y'l'--'- G'\ --) /) (=^

\ ^:-r^L- D---.:-

r. Qc'BLANCo 9.-.,--zo

Ftc. 1. The Cerro Blanco area

1982);Linare.s & Latone (1969)determined a IVAI age classified these pegmatitesas Rare Elements Class, of 350 * 30 Ma for the pegmatites.Benyacarite was Beryl{olumbite-Phosphate type, hybrid to the NYF found in oneof thesepegmatites, in the El Criollo mine. family, basedon the classificationof Cernf (1991). The main body of the pegmatiteis elongate(150 m) Feldspar,quartz, beryl and minor columbite-antalite with a north-south orientation and a 60-m-wide oval are mined from these pegmatites. As reported by section (Gallager& Jutorln 1971). Galliski (1994) Hurlbut & Aristarain(1968), Gay (1968,L973,1990, 7r0

1993),Schalamuk (190), andGay &Lira(1987), they are secondaryapatite, in some casesaccompanied by characterizedby high contentsof phosphateminerals, scarce dark purple phosphosiderite and torbernite. both primary (triplite and apatite) and secondary. Massive benyacaritewas identified in continuity with Triplite is the most commonprimary phospharemineral: phosphosiderite;it can be distinguishedby its green it occursin nodules,some of them quite large(up to 4 m color in contrastto the pink coloration of the earlier- in diameter),commonly showing alteration along the formed phosphosiderite. surfaceand fractures.Together with the triplite relics, there are considerableamounts of secondaryphos- AppBanaqceAND PHySIcAL PRoPERTES phaies, such as phosphosiderile,stengite, and rock- bridgeite,together with minor quantitiesof lipscombite, Benyacariteoccurs in euhedralcrystals ranging from dufr6nite,libethenite, bermanite and hentschelite; some 0.2 to 0.3 mm in size.The observedforms are {010}, fluorine-rich speciessuch as fluellite and pachnolite {111} and{001}, with {100} lesscommon. The habit havealso been observed, suggesting that a fluorine-rich is commonlytabular, with prevalenceof {010} (Ftg. 2); paragenesismigbt be essentialfor the formation of in somecrystals, {111} is better developed,thereby benyacariteand of the paulkenite-group minerals in attaining an almost equidimensionalhabit (Fig. 3). Its general. The most cornmon secondaryphosphate is color is greenishyellow, in some caseslight brown, phosphosiderite,a mineral mainly pink in color that probably owing to partial alteration. Other properties occurs both as idiomorphic crystals and in massive are:transparent to translucenl colorlessstreal<, vitreous form, and also as porous bluish-purple massesin a luster,no fluorescenceunder ultraviolet radiation,hard- matrix to the benyacarite.Small crystalsof benyacarile ness 2.5-3, cleavageperfect on {010}, very brittle, have also been observedimplanted on sfrengite and uneven fracture, and tendencyto break atong {101} pachnolite ia 4 minelal associationdominated by owing to parallel growth. Benyacariteis pale yellow in thin section,without pleocbroism,biaxial (+), 2V = 60(3)' (measuredin thin sectionusing a universalstage), with orientationX ll b, Y ll c, Z ll a. The indices of refraction, measuredon (001) euhedral crystals using an uniaxial stage, are: ct 1".612(3),P 1.621(3)afiy 1.649(3).Application of the Gladstone-Dalerule (Vlandarino 1981) gives a calcu- lated averageindex of refraction neebequal to 1.628, and the compatibility index is accordingly'osuperiof'.

(111) )----+- iro'l, /

Frc. 3. SEM micrographof a benyacaritecrystal showing an Ftc. 2. SIIAPE drawing of a benyacaritecrystal. almostequidimensional habit. BBNYACARITE. A Ti.BEARING PHOSPHATE 7tL

X-Rav-DrsnecTroN SruDrEsAND compositionalrelationships arnong these speciesoare Cnurncar, ANALYS$ summarizedin Tables1 and2, respectively.The empirical formula ofbenyacarite, calculatedon the basisoffour The X-ray powder-diffraction pattern, recorded P atoms, is (H2O6.4lQ.rol'{ao.m)zTi(Mn2+VotsF€*o.zr using a Gandolfi Camera(114.59 mm in diameter,Si as Mgo.oa)z(Fd*o.nTi4s.2sA10.07)z@Oa)a(Oo.oFo.4bL 4HaO. internal standard)wittr Ni-filtered CuKcr radiation, is reportedin Table 3owhere observed and calculatedd1,/.j Cnvsrar-Crmprcar- RxLATroNsmsro are compared.A comparisonwith conespondingdata Ofifin Spscrs for paulkerriteand mantienneiteclearly showsthat all these minerals are isostucfiral. The indexation pro- On the basis of the sfiucture determinationcarried posedfor the benyacaritespectrum differs only in a few out on benyacarite,and of detailed discussionof the lines from that ofpaulkerrite and,at leastfor the largest subjectreported by Demartinet aL (1993),the following d7,gvalue.s, is the sameas for mantienneite.The unit-cell general chemical formula for the paulkerrite-like parametersobtained from refinement of the powder- mineralscanbederived:(tlzO,K)zTiM(I)2M(2)2eOi4 diffraction data t4 10.55(L),b 20.49(4),c 12.52G)Ll (O,D2.14H2O.The M(1) site is mostly occupiedby are in good agreementwith those obtained from the Mn2* and someFd* in benyacarite,by Mg andMn2+ in single-crystaldata. paulkerrite,and by Mg and someFeP+ in mantienneite. A fuIl descriptionof the delerminationof the crystal In the M(2) site, Fe3* prevails in paulkerrite and in sfructure and of the chemical composition has been benyacarite,whereas in mantienneite,this site is essen- reported elsewhere@emartin et al. 1993). The unit- tially occupiedby Al. In spite of the lack of crystal- cell datafor all mineralsrelated to benvacarite.and the stucture bformation, the interpretationof the chemical analysisfor both paulkerriteand mantienneite grven by Peacoret al. (1984) and by Fransoletet aI. (1984) is closetoourinferences. The differences mostly concemfte role of potassium,which can be extensivelyreplaced by H2O molecules,and the possibiJitythat someFd*, as well as the dominsnl Fe3*,may occur in mantienneite. TABLE 3. X.RAY POWDER.DIFFRACNON DATAFORBENYACARIE Another mineral recentlyreported in the literatureis the so-called"mafveevite", not approvedas a new specie's hktwded-h (Kydryashova & Rohzdestvenskaya7991., Puziewicz 0 z 0 90 t0.29 t0.292 1D3). Thechemical composition as given by theseauthors 1 I I 80 7.51 7.514 andrecalculated on the basisof 4 P atomsis reportedin 0 0 2 100 6.26 6.258 Table 2, and comparedwith the other mineralsof this 0 4 0 40 5.16 5.146 group. On the basis of these data, together with the 22054.704.698 similalily of the unit-cell parameters,crystal habi! and t41 14.324.339 X-ray-diffraction pattern,there seemsli6le doubt that 212403.963.960 "matveevite"belongs to the paulkerriteseries. The only group (Pmcn ot Y2pn 2 2 2 50 3.76 3.757 relevant differenceis the space be incorrect.On 0 0 4 100 3.13 3.t29 instsadof Pbca)"which may, however, idealformula of benyacarite,where Mfi 312 13.023.034 consideringthe and Fe3*prevail in the M(1) nd MQ) sites, respect- 0 2 4 20 2.99 2.993 ively, 'omatveevite"can be describedas a Mg- and | 2 4 40 2.88 2.880 Al-rich variety of benyacarite,occurring in a similal 1 5 :l 20 2.813 2.8n paragenesis.The extensive substitution of Mn2* and 2 6 rl 2.803 Fe3t by lighter elementsaccounts for the lower values 342 30 2.635 2.635 of its indicesof refraction. 4 | r'l 20 2.560 2.563 25tl 2.562 The structureof theseminerals is characterizedby 2 3 4 l0 2.507 2.506 the presenceof layersperpendicular to [010] containing 442 12.t932.t99 two kinds of octahedra,M(2)Os(O,n and TiOs(O"F); presencemay be essential,is 5 0 I l0 2.082 2.04 the fluorine atom, whose betweensuch different octahedra-On both sides 3 I 5 10 2.030 2.030 shared of theselayers are POa tetrahedr4 with oneface ap'proxi- 4 2 4 20 1.980 1.980 mately parallel to the layers. The three cornersof this 4 3 4 10 1.935 1.935 face areshared with octahedracentered on Ti aildM(2), corner is sharedwith M(L)O6 Gardolfi cmera, 11459 rm in dim€t€r. Ni-filt€red whereasthe remaining CuKa radidion The imeasities vrere esilim&d octahedron.The network of octahedraand tefrahedra visnlly, resultsin cavitiesoccupied by Kt and H2Omolecules. 712

ACKNowI-EDGEIVGTITS -(1993): Hentschelitaen Ceno Blanco, Tanti, C6rdoba- Revistade la AsociacidnGeol.6gica Argewina 4E,n7 :282,

The financial assistance of the Italian National & Lm,c, R. (1987): Fluellita del Co. Blanco, Tanti, Research Council (C.N.R.) and MURST is gratefirlly C6rdoba.Asociaciln Argenritn de Mineralogia.Petrolagia acknowledged. The authors are also gratefirl to Prof. E. y Se dimentolo gia 8, n -32. Galli and an anon)rmous referee for useful suggestions. Hurr.sln, C.S. & Assranaw, L.F. (1968):Bermanite and its occurrencein C6rdobaArgiliaa" AnLMirEraI53,41643l. Rmrnrncus KyDRyAssovA,V.I. & RoHDFsrvBrsKAyA,I.V. (1991):New dmrf, p. (1991):Rare-element granitic pegmatites. I. Anatomy minerals. fr-Y. fup. Vses.Mineral. Obshchest.120(4), andintei:ral evolnion of pegnatite.sdepo$ts. GeoscL Condn 100-115(in Russ.). r$Q),49-67. LrNArEs,E. & l,aronns, C.O. (1969):Edades potasio-arg6n y Dnrrren:rw,F., Pnarr, T., Gav, H.D. & Gneuecqou, C.M. plomo-alfade rocasgraniticas de las Provinciasde C6rdoba (1993):The crystal structureof a mineral related to paul- y San Luis. Actas 4o Jornad.asGeoldgicas Argentfuws 2, kerite. Z Kristallogr. 208, 57-7 L, 1,95-2M.

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