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Chladniite, Narcamgr(Poo)U: a New Mineral from the Carlton (IIICD) Iron Meteorite

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Chladniite, Narcamgr(Poo)U: a New Mineral from the Carlton (IIICD) Iron Meteorite 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 FederalCenter, 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.
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