American Mineralogist, Volume 79, pages 375-380, 1994

Chladniite, NarCaMgr(POo)u: A new mineral from the Carlton (IIICD) iron meteorite

Trvrorny J. McCov Planetary Geosciences,Department of Geology and Geophysics,School of Oceanand Earth Scienceand Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, U.S.A. I.q,NrM. Srnrr,n Department of the GeophysicalSciences, University of Chicago, 5734 S. Ellis Ave., Chicago,Illinois 60637, U.S.A. Kr,lus Knrr, Planetary Geosciences,Hawaii Center for Volcanology, Department of Geology and Geophysics, School of Ocean and Earth Scienceand Technology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, U.S.A. B. F. Lnoxano U.S. Geological Survey, Box 25046, M.S. 905, Denver Federal Center, Denver, Colorado 80225, U.S.A. MlcNus ENonns Institut ftir Planetologie,Westflilische Wilhelms-Universit?it, D-4400 Mi.inster,Germany

Ansrntcr A new mineral, chladniite, NarcaMgr(Poo)u, occurs as a single grain within a silicate- bearing inclqsion in the Carlton (IIICD) iron meteorite. It is hexagonal, R3, a : 14.967, c : 42.595 A. tt is named for E.F.F.Chladni (1756-1827),who is widely regardedas the founder of the scienceof meteoritics. Chladniite is colorlessand transparent when pow- dered. In polished section, the mineral is gray, dark, weakly bireflecting, and weakly an- isotropic. Cleavage,rarely visible, is rhomboidal in plan. Polishing hardnessis less than low-calcium orthopyroxene, but greater than Fe,Ni metal. Reflectancemeasurements at -- 589 nm give R, : 5.3o/o,R, 5.60/o.Assuming an absorption coefficient k : 0, the cal- culated refractive indices are nt : | .60, n, : | .62. Strongerreflections on Gandolfi X-ray film of chladniiteare d:3.694 (0,l,ll;306) s, 3.558(0,2,10;0,0,12) m,2.960 (0,1,14) s, 2.753(1,3,10) s, 2.500 (3,3,0) m, 2.126(2,4,10 2,3,14;0,2,19) m, and 1.851(701; 1,5,14; 6,0,12)m. Microprobeanalysis gives, in weightpercent, NarO 6.57,CaO 6.59,MgO 33.5, FeO 2.23, MnO 0.30, SiO, 0.59, P2O549.9, total 99.68,leading to the empirical formula Na, ,rCaonrSio or(Mg. nuFeo,ruM'o oo)r:r ru(Po rrOo)u. Chladniite is the Mg analogueof fillowite and johnsomervilleite, which are Mn- and Fe-dominated end-members, respectively. Chladniite occurswith chlorapatite,olivine, orthopyroxene,plegjoclase, schreibersite, Fe,Ni metal, and troilite.

INrnooucltoN meteorite,which was found in 1887near Carlton, Ham- The IIICD iron meteorites are a small group (20 in ilton County, Texas. This section is the holotype for total; seeWasson et al., 1980,forthe definitionand mem- chladniite and is in the meteorite collection of the Na- bership of group IIICD), three of which contain silicate- tional Museum of Natural History, Smithsonian Institu- bearing inclusions rich in troilite, graphite, schreibersite, tion, Washington, DC. Chladniite occurswithin and near and phosphates.These inclusions have yielded a number the edge of a silicate-bearinginclusion that is approxi- of new and unusual phosphates,and the Na, Ca-, and mately 5 x 5 mm in size. Chlorapatite is the dominant Mg-rich phosphatesbrianite and panethite were first de- mineral in the inclusion (69.8 volo/o).Olivine, pyroxene, scribed from the IIICD iron meteorite Dayton (Fuchs et and plagioclase(12.8 volo/ototal silicates)occur as mono- al., 1967).During a study of silicate-bearinginclusions in or polymineralic clusters within chlorapatite and along IIICD iron meteorites(McCoy et al., 1993),we have dis- the distal portions ofthe inclusion. Averagecompositions covered a new naturally occurring phosphate, of inclusion minerals are Faro*', (N : 8) for olivine, NarCaMgr(POo)u,which we have named chladniite. FSn,u=o,oand Wo,u*0, (N: 9) for low-calcium orthopy- roxene,and Anr,,*ro and Or37*0e(N: 9) for plagioclase OccunnnNcn (deviations are lo of compositional variability, and N A single grain of chladniite was identified in polished values are number of analyses).Schreibersite (3.9 volo/o) sectionUSNM 2707 (Fig. l) of the Carlton (IIICD) iron occurs as millimeter-sized grains, and an intergrowth of 0003-004x/94l0304-0375$02.00 37s 376 McCOY ET AL.: CHLADNIITE, Na'CaMg'(POo)u

pearance;however, observation ofareas free ofthese veins suggeststhat chladniite is transparent and colorless.

Osrrclr PROPERTTES The thickness of polished section USNM 2707 pre- vented the observation of the optical properties of chlad- niite in transmitted light. The possibility of measuring the optical properties in transmitted light on the small piece extracted for X-ray studies was rejectedbecause of the precious nature of the material, its minute size' and the substantialrisk oflosing this piece.Optical properties were determined by observationsin reflectedlight on the polished thick section. Experimental conditions for the measurementsin vertically incident, vertically reflected plane-polarized light were mineral surface cleaned with l. Reflectedlight photomicrograph of chladniite and ad- Fig. methanol; reflectancestandard Zeiss NGl, no. 064, R jacent phasesin the Carlton (IIICD) iron meteorite. Chladniite (589 nm) :4.42o/o; the effectivenumeric apertureof ob- (Ch) occursas an irregularly shapedgrain at the edgeofa silicate- jective Smith type; running interference bearing inclusion. Silicatesare olivine (Ol), pyroxene (Px), and 0.35, reflector of plagioclase (Pl). Chlorapatite (Ca) is the dominant phase within filter Veril 5200, band width 12 nm; photomultiplier RCA the inclusion. Schreibersite(Sc) is in contact with chladniite. Fe,Ni I P28. metal (M) enclosesthe entire assemblage.Scale bar : 200 pm. Chladniite in polished section is glay, dark (slightly darker than the adjacent orthopyroxene), weakly bire- flecting, and weakly anisotropic without polarization col- ors. Internal reflection is orange-brown and pervasive, micrometer-sized Fe,Ni and FeS occurs as millimeter- the color probably an effect of the associatedalteration sized pockets (12.7 volo/o)at the edgesof the inclusion. products.Cleavage, outlined by alteration products in one The entire inclusion is rimmed by swathing kamacite. minute area, is rhomboidal in plan and thus very likely Complete descriptions of other inclusions in Carlton are rhombohedral in three dimensions. Polishing hardnessis given by McCoy et al. (1993). lessthan that ofpyroxene, but greaterthan that ofFe,Ni metal. Examination of the grain after drilling revealsnu- AppnlnaucE AND pHysIcAL PRoPERTIES merous domains 10-20 pm in diameter that have differ- : : Chladniite occursas a singlegrain, which measures175 ent optical orientations.At 589 nm, R' 5.3o/o,Rz : x 975 pm (Fig. l). The small size of the grain prevented 5.4o/oon one area, 5.5 and 5.60loon another. If k 0 the measurement of many physical properties, such as (completetransparency), n,: 1.60 and nr: 1.60for the streak, hardness,and density. Some physical properties first area;n,: l.6l and nr: l'62 for the second.The - were observed in reflected light using a Nikon binocular relationis n: (l + \,{fy(l VR), whereR is a decimal microscope. The luster is vitreous to resinous. Irregular value. This is a transposition of the familiar Fresnelequa- fracturesare filled with hydrated iron oxides ofterrestrial tion, R : (n - l)'z/(n + l)'?(see, for example,Galopin origin. Theseveins give the mineral an orange-brownap- and Henry, 1972, p. 92). Yery low bireflectance' com-

TABLE1, Microprobe analyses (wt%) of phosphates from the lllOD iron meteorites Dayton and Carlton

Dayton Carlton Panethite Brianite Whitlockite Chlorapatite Chladniite

Naro 13.8(2) 20_6(3) 2.67(s) 0.23(3) 6.6(1) Mgo 25.0(21 13.4(1) 3.67(21 0.45(4) 33.5(2) P.o" 47.6(41 46.8(3) 45.6(3) 40.s(4) 49.9(4) CaO 6.28(8) 19.3(1) 48.0(3) 54.7(2) 6.59(2) FeO 4.s(3) 0.38(4) 0.3s(8) 0.25(s) 2.2(2) MnO 0.48(5) bd bd 0.06(1) 0.30(6) KrO 1.1 9(3) bd 0.04(1) bd bd sio, 0.13(3) bd M bd 0.5s(8) 0.11(1) bd bd 4.18(8) bd F bd bd bd 1.64(4) bd 99.49 100.48 100.37 102.01 99.68 O = Cl,F 0.02 0.00 0.00 1.6iit 0.00 Total 99.47 100.48 100.37 100.38 99.68 /v 5 5 5 5 c /Vote:bd : below detection.Values in parenthesesare uncertaintiesin the last digit and are equal to 1d compositionalvariability' N: no. of analyzed points. McCOY ET AL.: CHLADNIITE, Na,CaMg,(pOo)u 377

:24) TABLE2. Chemicalformulas (O for phosphatesanalyzed in this work comparedwith data in the literature Hanethtte this work (NaoerlGz)r=4 14Cao*(Mgu n"Feo.Mno6)r_6 !2(Poso.)6sioozclo@ Fuchser at. (1967) Nfu soao 6rlGr1 (Mg5 loFeoaMno 21L_...(Po*Oo). Brianite this work Nas $Cas io(Mg3 @Feoo.)r_. ou(Po*On)u Fuchset al. (1967) ideal, Na6ca3Mgs(PO4)6 Whitlockite this work Nfu 7e(Ca7sMgo eFeo 6)>=67o(Po eeo4)6 Fuchs et at. (1967) Nao $(Ca7 sMgo sTFeomL_s 5s(POn)6 Chlorapatite this work Naoo6(Ca,o @Mgo,2Feo sMno o,)>_ro26(Po $O4)6(Cl1 zFo s)r_211 ideal Ca,o(P01)6C1, Chladniite this work Na, rrOao *(Mgu *Feo 26Mnod)r-7 26(PosOi)6Sio @ ideal Na,CaMgT(POi)6

bined with the small areas free from internal reflections these analysesare given in Table l. Care was taken to or alteration products, prevented measurement of the avoid veins ofterrestrial weathering products during the complete dispersion curves. analyses. The lack of natural or synthetic microprobe Absorption coemcient k could not be determined by standardsof similar composition to chladniite prompted the two-media method becauseimmersion oil enhanced us to analyzefour other, previously analyzed,phosphates the internal reflection of the mineral and made the mea- (panethite,brianite, and whitlockite in the Dayton IIICD i-R surement of invalid. The assumption that k : 0 iron meteorite; chlorapatite in Carlton) to test our ana- (complete transparency)is based on the presenceof lytical method. Our analysesand, hence,calculated min- white, transparentparticles lining the raggededges of eral formulae (Table 2) differ only slightly from previ- the hole drilled to remove material for X-ray study.The ously published data, thus attesting to the reliability of reproducibility of R in the 5-60lorange is no better than our analyses. +0. 1oloabsolute. Thus, the birefringenceof chladniite is not reliably given by subtracting n, from nr, the true MrNnnql FoRMULA birefringenceis probably closerto 0.01 than 0.02. Im- Calculatedmineral formulae for all five phosphatesan- precision in the measurementof R also leavesthe op- alyzed in this work are given in Table 2. Formulae for tical symmetry of chladniite in doubt. It is possiblethat panethite, brianite, and whitlockite from the Dayton me- : R, 5.4 + 0.10/o represents Ro and Ru : 5.5 + 0.l0lo teorite agreewell with those given by Fuchs et al. (1967\. representsRi, making the mineral uniaxial (+), but the The formula for chlorapatite from Carlton agreeswith sensitiveconoscopic test for the uniaxiality of monore- the ideal formula. The ideal formula for chladniite is flecting sections is unsatisfactory,owing to reflection Na,CaMgr(POo)u. from adjacentweathering veinlets. The formula of chladniite suggeststhat it is related to There can be no grosserror in the calculatedvalues of two rare minerals, fillowite and johnsomervilleite. Fill- n, and nr, for the adjacentpyroxene has at 589 nm, R, : owite has the ideal formula of Na,Ca(Mn,Fe),(POo).(Ara- 7.2o/o,R, : 7.4o/o,giving n, : 1.73, n, : 1.75.These refractiveindices fall within the range 1.723-l.j76,bi- refringence0.017-0.023, reported in the literaturefor or- Mg thopyroxeneswhose composition differs little from that ofthe pyroxeneanalyzed in Carlton.

CorvrposrrroN The composition of chladniite was determined using a CamecaSX-50 electron microprobe. Conditions of the analyseswere a beam l0 pm in diameter, l0-nA incident current, l5-keV acceleratingvoltage, and 30-s counting times on peak and background positions. Data were cor- rected using the manufacturer-supplied pAp ZAF pro- gram. Standards used were jadeite for Na, hypersthene for Mg, Marjalahti olivine for Si and Fe, Verma garnet Johnsomervilleite for Mn, orthoclase for Al and K, and apatite for Ca, p, F, and CI. Minimum detection limits are 0.02 wto/ofor Cl, NarO, and K,O; 0.03 wtolofor MnO, SiO,, and MgO; Mn Fe 0.04 wto/ofor FeO; and 0.05 wto/ofor F. All phosphates Fig.2. Ternary plot showing the relationship betweenchlad- analyzed in this study, including chladniite, have AlrO, niite, fillowite, and johnsomervilleite. All have the generalfor- contents below the detection limit of 0.02 wto/o. mula NarCaX,(PO.)u,where Xis Fe,*, Mg2*,or Mnr*. Data for The averagecomposition of chladniite, calculatedfrom fillowite (triangles) and johnsomervilleite (circles) are summa- five analyses,and the 1o compositional variabilities of rized in Araki and Moore (1981). 378 MoCOY ET AL.: CHLADNIITE, Na'CaMg'(POo)u

johnsomervilleiteand fillowite TleLe 3, Values for d and approximate intensitiesof chladniitecompared with Johnsomervilleite Fillowite 18-51 6 Chladniite JCPDF 33-1224 JCPDF d(A) d.""" (A) l"o 4". (A) hkt d(A) lo 14.5 5 11.2 50 11.4 35 8.19 5 8.49 20 7.20 1 7.35 J 6.75 5 6.22 2 6.37 5 5.60 2 5.69 10 5.16 2 5.29 10 4.91 5 5.16 5 4.48 10 4.57 10 4.30 10 4.37 4.12 10 4.25 5 40 3.694 s 3.710 0,1,11 3.70 70 3.789 3.691 306 3.716 c 60 3.558 m 3.560 0,2,10 3.55 70 3.640 3.550 0,0,12 3.48 D 3.492 10 3.326 5 3.397 10 3.209 5 3.293 5 3234 10 5 3.085 w 3.095 137 3.109 5 3.172 3.029 10 70 2.960 s 2.962 0,1,14 2.965 70 3.017 2.935 10 2.896 10 2.873 5 2.843 10 100 2.753 s 2.747 1,3,10 2.764 100 2.814 2.637 2 2.692 10 2.595 2 2.647 10 60 2.500 m 2.495 330 2.501 40 2.552 241 2.443 10 2.500 5 2.459 w 2.446 5 2.354 w 2.353 336 2.355 10 2.442 2.408 10 2.310 2.390 c 2.269 2 2.367 10 5 2.226 w 2.214 0,5,10 2.221 2 2.25 2.212 1,4,12 2.'t6 20 2.126 m 2.123 2,4,10 2.129 10 2.127 2,3,14 2.119 0,2,19 2.085 2 2.10 5 2.045 2 2.04 5 2.008 2 2.O1 5 1.973 w 1.965 609 1.971 2 1.962 2,4,13 1.94 5 1.920 w 1.916 2,3,17 1.918 2 1.888 40 1.851 m 1.850 701 1.852 20 1.849 1,5,14 1.845 6,0,12 1.824 10 1.853 5 1.831 10 1.796 10 1.81 5 1.7404 10 1.715 w 1.713 1.675 5 1.69 J 1.656 5 1.66 5 1.645 1.64 J 1.616 c 1.61 5 1.59 5 1.588 w 1.586 c 1 568 1.57 c 1.549 J 1.496 5 1.51 10 1.492 w 1.490 1.460 2 1.46 10 1.442 I 1.418 2 1.41 5 1.16,15;1.12,10 1.351 no 1.39,5; : : Nofe.',.", values tor chladniite:-: not observed,s: strong,m medium,w weak; nd: no datum' McCOY ET AL.: CHLADNIITE, Na,CaMg,(POo)u 379

ki and Moore, l98l) and is the Mn analogueof chladniite. with spacegroup R3, as for fillowite (Araki and Moore, Johnsomervilleite is the Fe-dominated analogue,whose 198l). Precessionphotographs confirm the symmetry, and formula is given as Na,oCa.Mg,,(Fe,Mn)rr(pOo)ru (Living- no additional diffractions were noted on theseprecession stone, 1980).All three minerals sharethe general,sim- photographs, indicating that the fragment is not poly- plified formula NarCaXr(POo)u,where X is Mg2*, Fe2*, crystalline. Based on these data, we suggestthat chlad- or Mn2*. However, whereaschtadniite is closeto the Mg niite is isostructural with fillowite, but. becauseof the end-member, fillowite has appreciableamounts of Fe and small crystal size,a data set suitable for crystal structure johnsomervilleite appreciable amounts of Mg and Mn refinement has not as yet been obtained. However, the (Fig. 2). The empirical formulae of both chladniite and structure determination of NaoCarMgr,(POo),r,a com- johnsomervilleite show excessesof divalent Mg, Fe, and position close to chladniite, is isostructural with fillowite Mn and depletions in Na* relative to the ideal formulae. (Domanskii et al., 1982).The small differencein com- It appearsthat in both minerals the divalent cations sub- positionbetween chladniite, NauCarMgr, (POo),r, and this stitute for the monovalent Na. compound is consideredto be within the recognizedcom- positional uncertainty, as discussedby Araki and Moore X-ru.y sruDrEs (1981)for the caseof fillowite. Obtaining a sample for X-ray study from the unique occurrenceof chladniite in a polished section presented MrNrn-lL NAME a challenge. After optically selecting an area free from Chladniite is named for Ernst Florens Friedrich weathering veins 50 pm in diameter, a Medenbach dia- Chlad- m (1756-1827). Chladni (1794) published pioneering mond drill affixedto a Zeissmicroscope was usedto scribe a book that, for the first time, presented a shallow trench, leaving a tapered spindle about 50 pm strong evidence for an extraterrestrialorigin of meteoritic in diameter at the baseand 30 ptmin diameter at the top. stonesand iron meteorites.Prior to that work, it Drilling left -800/oof the mineral intact for future studies, was widely acceptedthat meteorites formed by condensation including many areas 10-40 pm in size free from terres- of solid matter in clouds. Chladni's work set trial weathering veins. This spindle was removed from the stagefor the development of the scienceof meteoritics, from which the sample using a surgical scalpel. The resulting frag- we have learned much about the origin and ment measuresabout 20 x 30 x 30 pm and was attached evolution of the solar system. to a glassfiber for X-ray study. Chladni is widely regardedas the father of meteoritics. It is particularly appropriate that a meteoritic Using a Gandolfi camera57.28 mm in diameter,Mn- mineral be named in his honor, as we mark filtered FeKa radiation, and a 6-d exposure,a diffraction the bicentennialof the publication of his book. The mineral pattern was obtained consisting of 17 measurablelines. and mineral name have been approved by the Commission Thesedata, converted to d values,and their approximate on New Min- erals and Mineral Names of the International intensitiesare given in Table 3. For comparison,calcu- Mineral- ogical Association. lated d values obtained from the cell constants from a single-crystalcell refinement and the diffraction panerns for johnsomervilleite and fillowite (JCPDF 33-1224 and, AcxNowr,nncMENTS l8-516, respectively) are included in Table 3. Although This work would not have been possiblewithout the unwavering sup- most matchesbetween the observedand calculatedspac- port of R.S. Clarke, Jr., of the U.S. National Museum, Smithsonian In- ings for chladniite are good, those for the weakest dif- stitution, Washinglon,DC. We also acknowledgehelpful discussionswith fractions are poorer, probably becauseofthe difficulty of E.J. Olsen and P.B. Moore of the University of Chicago. Constructive reviews by E.J. Olsen and G.E. Harlow significantlyimproved accurate measurement.The apparent absence the manu- of strong script. This work was supportedin part by NASA grantsNAG 9-454 and diffractions with d valuesgreater than about 4 A in chlad- NAGW-328 I (K.K., Principal Investigator)and N AG 9-47 (LM.S., prin- niite is due to the broad darkening ofthe film causedby cipal Investigator).This is PlanetaryGeosciences publication no. 742 and scattering from the fiber and glue. Indications of many SchoolofOcean and Earth Scienceand Technologypublication no. 3063. weak peaksin the rangeof 1.9-1.3 A are presenton the film but could not be accurately measured. The close RrrnnrNcns crrED match among the three diffraction patternsgiven in Table Araki, T., and Moore, P.B. (1981) Fillowite, Na,Ca(Mn,Fe)l+(POo)u:Its 3 strongly suggeststhat the structuresare similar. crystal structure.American Mineralogist, 66, 827-842. A four-circle single-crystalstudy provided both refined Chladni, E.F.F. (1794) Uber den Ursprung der von Pallas gefundenen cell parameters and a set of diffraction intensities. The und andererihr iihnlicher Eisenmassen,63 p. Hartknoch, Riga, ktvia. cell parameterswere obtained by least-squaresrefinement Domanskii, A.I., Smolin, Yu.I., Shepelev,Yu.F., and Majling, J. (1982) Determination of crystal structure using 20 centered of triple magnesiumcalcium sodium diffractions, each the averageofauto- orthophosphateMg,CaoNao(POo),r. Soviet Physics-Crystallography, matic centering of eight equivalent diffractions. The re- 27, 535-537. sultingcell parameterc are a: 14.967+ 0.002,c : 42.595 Fuchs, L.H., Olsen, E., and Henderson,E.P. (1967) On the occurrenceof + 0.004 A, B : 120", cell volume : g263.6 Ar. The brianite and panethite, two new phosphateminerals from the Da14on meteorite. Geochimica et CosmochimicaActa. 31. l71l-1719. calculateddensity is 3.01 g,/cm3,with Z: 18,as for fil- Galopin, R., and Henry, N.FM (1972) Microscopic study of opaque lowite. Systematicabsences of difractions are consistent minerals, 322 p. Hetrer, Cambridge,England. 380 McCOY ET AL.: CHLADNIITE' NarCaMg'(PQo)e

Kracher, A' (1980)Origin of iron Livingstone, A. (19S0) Johnsomeryilleite, a new transition-metal phos- Wasson,J.T., Willis, J., Wai, C.M., and groups Zeitschrift fiiLr Ndturforschung, 35a' phate mineral ftom the Loch Quoich area, Scotland. Mineralogical meteorite IAB and IIICD. Magazine,43,833-836. 781-795' McCoy, T.J., Kdil, K., Scott, E.R.D., and Haack, H, (1993) Genesisof the IIICD iron meteorites: Evidence from silicate-bearing inclusions. Mxruscnrrr RECETVEDJuNe 28' 1993 Meteoritics. 28,552-560. Mer'ruscp'rrr ActEPTEDNoveusER 24' 1993