Corrosion of Fe-Ni Alloys by Cl-Containing Akagan6ite (P

American Mineralogist, Volume 74, pages 656467, 1989

Corrosion of Fe-Ni alloys by Cl-containing akagan6ite(p-FeOOH): The Antarctic meteorite case YacN F. Bucnwar-o Department of Metallurgy, Building 204, The Technical University, 2800 Lyngby, Denmark Rov S. Cr-anrc, Jn. Division of Meteorites, National Museum of Natural History, Smithsonian Institution, Washington,D.C. 20560, U.S.A.

Ansrnacr A suite of 12 iron and 8 stony meteorites from various environments and locations in Antarctica was studied, representinga range of compositions, metallographic structures, and degreesof weathering. Polished sectionsof meteoritic metal with adhering corrosion products were examined microscopically, with the electron microprobe and seu, and were used as samplesfor X-ray diffraction examination. The major corrosion products are Cl- containing akagan6ite(up to 5 wto/oCl) and goethite, with minor amounts of lepidocrocite and maghemite. Cl is not native to the meteoritesbut, owing to the electrochemicalnature of the corrosion of Fe-Ni alloys, is attracted from the snow and ice, or rocky soil, environment that contains low amounts of Cl. Akagan6iteprecipitates near the reaction front, incorporating Cl ions into ion-exchangesites, where they may be retained, made available for further depassivating,corrosive action, or become flushed from the system.With time and distance from the reaction surface,akagan6ite ages and transforms to mainly goethite and maghemite. It is again argued that lawrencite (Feclr) is not a mineral in meteorites. In the stormy Antarctic, wind-blown terrestrial particles may become attached to the weathering products on the meteorite and in time themselvesdecompose, delivering terrestrial ions to the meteorite corrosion system.The ions may move a significant distance from the surface,and in particular Cl may be found along almost invisible cracks in the deep interior. Trace-elementwork and agedeterminations (36C1)should take this problem lnto account.

INrnonuctroN study of iron-meteorite corrosion in all terrestrial environments. Although a number of recent papershave con- Meteorites are our most accessiblesamples of extrater- sidered various aspectsof the weathering of stony mete- restrial bodies. They provide us with direct evidence of orites, little attention has been given to iron meteorites early planetary systemprocesses, along with information since the works of Buddhue (1957), White et al. (1967), on many subsequentinteractions throughout their com- Faust et al. (1973), and Buchwald (1977). plex histories prior to and after arrival on the Earth. They Early in our studies it was realized that Cl-containing fall randomly in terms of both time and geographicdis- akagan6iteis a mineralogical key to the understandingof tribution. Our life-supporting atmosphere laden with the corrosion of meteoritic metal and that its role is most oxygen and moisture, however, is hostile to theseintrud- clearly demonstrated by the comparatively simple asso- ers from the less reactive environment of space.Corro- ciation of corrosion products that developson meteorites sive processesbegin as a meteorite entersthe atmosphere retrieved after long exposuresto the cold and low-hu- and continue until nothing remains that is recognizable. midity environment of Antarctica (Buchwald and Clarke, The metallic phasesthat are present in all but a few me- 1988). The processthat emergesand overcomespassiv- teorites are among the first to show obvious effects of ation barriers includes anodic metal going into solution, terrestrial weathering. Two Fe-Ni alloys, kamacite (low- Cl- ions that originate from the terrestrial environment Ni Fe-Ni, bcc) and taenite (high-Ni Fe-Ni, fcc), are the moving to the reaction surface to maintain charge bal- main metallic minerals present, and they are gradually ance, and Cl-containing akagan6iteprecipitating at the converted to rust. Understanding this corrosion process reaction surface.Over time, the initial corrosion products has obvious implications for developing strategiesto ter- undergo an aging processthat converts them to mainly minate, or at least minimize deterioration that continues goethite. This same process is also responsible for the when these scientifically important materials are incor- corrosion of the metal particles in Antarctic chondrites, porated into researchand exhibit collections. For these stony meteoritescontaining from 6 to 15 wt0/ometal. Pre- and other reasons,we have undertaken a comprehensive liminary indications are that Cl-containing akagan6ite 0003-004x/89/0506-o656s02.00 656 BUCHWALD AND CLARKE: CORROSION OF Fe-Ni BY AKAGANEITE 657

TABLE1, Characterizationof selectedAntarctic meteorites

Bulk comoosition". MaSS State of Aget Name' (kS) Type wt% Ni wt% P corrosion (10'yr) ALH A77283 10.5 lA, coarseoctahedrite 7.33 0.22 110+ 70 ALH 477289 2.19 lA, coarse octahedrite 684 0.21 170+ 70 ALH A78252 279 lVA, fine octahedrite 9.33 0.17 1 360+ 70 'I ALHA81013 178 llA, hexahedrite 55z 0.27 ALH 84165 0.10 lllA, mediumoctahedrite LIO 0.14 0 DRP A78OO9 138.1 llB, coarsestoctahedrite 6.59 0.34 2 EET 83390 0.o2 (lA), octahedrite 0.2+ 2 GRO 8s201 1.40 lllA, mediumoctahedrite 6,CY 0.23 0 tLD 83500 2.52 lVB, ataxite 189 0.28 -3000 NEP642614 1.07 lA, coarse octahedrite 7.26 0.20 'I PGP 477006 1eo lA, coarse octahedrite 727 0.20 90+70 Y 75105 0.02 llA. hexahedrite 5.26$ 0.25+ 0 - AllanHills (ALH), Derrick Peak (DRP), Elephant Moraine (EET), Grosvenor Mountains (GRO), Inland Forts (lLD), Neptune Mountains (NEP), Purgatory Peak(PGP), Yamato Mountains (Y). '- E. Jarosewich,analyst. Remainder is Fe with -1% total Co, S, Cr, C, etc. t Nishiizumi(1984) and Nishiizumiet at (1987). f Our estimate. $ Kracheret at. (1980).

plays an important role in the weathering of essentially provided the specimensis given by Marvin and Mason all meteoritic metal, and we suspectthat in the corrosion (1980,1982, 1984) and Marvin and MacPherson(1989). of other ferrous metals under similar circumstances,this Table I provides total specimenweights, chemical and mineral plays a role that has not been previously recog- structural classification,and bulk Ni and P values. The nized. severity ofcorrosion is also evaluated on a scalefrom 0 (no corrosion) to 4 (destructivecorrosion), a scalesimilar MrrnonrrB SpECIMENS to but different in detail from the scaleused for Antarctic After preliminary examination of corrosion products stony meteorites(Lipschutz, 1982). The final column re- on 40 iron meteorites from a variety of environments, ports terrestrialages (Nishiizumi, 1984;Nishiizumi et al., we focusedour attention on a suite of l2 Antarctic irons. I 987). Collectedbetween 1964 and 1986, they representa variety of compositions and metallographic structures,dif- ExpsnrN{nNTAL METHoDS ferent environments within Antarctica, and separations Regions with interfacesbetween metals and oxides or by large distanceson the continent (Table l). The Allan oxide fragments were selectedfor examination that in- Hills, Elephant Moraine, Grosvenor Mountains, and ya- cluded microscopic identification on polished sections, mato Mountains meteoriteswere found on either bare ice electron microprobe and scanning electron microscope or in an ice and rock moraine, generally at altitudes of (srv-eo,lx) analysis on these same sections, and X-ray 1600-2000m (Yoshida et at., t97t yanai, 1976; Cas- powder-diffraction studiesof oxide isolated from selected sidy, 1980;Clarke et al., l98l;Clarke, 1982a).The Der- sections. Polished sections were made in the standard rick Peak meteoriteswere found on a ridge and on a side way: cutting with tap-water-cooled carborundum blades, of Derrick Peak, a mountain protruding above Heather- followed by wet-grinding with garnet grit, and wet pol- ton Glacier in the Britannia Range (Kamp and Lowe, ishing with diamond and finally AlrO, paste.In order to 1982;Clarke, 1982b, 1984).The Inland Forts specimen establish that Cl was not introduced by the use of tap was found partially within soil at Inland Forts on the water, control sectionswere preparedwithout its use from south slope of the Asgard Range above Taylor Glacier corrosion products that had not been previously exposed (Clarke, 1989). The Neptune Mountains meteorite was to tap water. Dry cutting and coarse grinding were fol- found on glacial debris about 30 m above the rce on a lowed by petroleumJubricated fine grinding and polish- nunatak in the central Neptune Range (Buchwald, 1975). ing with diamond paste.Akagan6ite in thesesections con- The Purgatory Peak meteorite was recovered from the tained comparable levels of Cl and convinced us that Cl baseof the mountain in the Victoria Dry Valley (King et was not introduced or moved during our sample prepa- al., 1980;Clarke, 1982a).Common to thesespecimens is ration. However, it would be reasonableto expectthat in that they were found completely or largely exposed on proceduressuch as abrasive-wire sawing,where long cut- the ice, on rock surfaces,or on soil. Great care was taken ting times and large amounts of tap water are involved, to prevent contamination or deterioration of specimens a slight modification of the mobile Cl concentration in during collection and transport to curatorial facilities, and akagan6iteis possible. they have received special attention within these facili- Chemical data were obtained with an anr- seuq elec- ties. Backgroundon the field and curatorial programsthat tron microprobe with six fixed spectrometersfor Si, Al, 658 BUCHWALD AND CLARKE: CORROSION OF Fe-Ni BY AKAGANEITE

TABLE2. Oxide weathering products of Antarctic iron meteorites

Observedrange (wt%) Formula Name Structure Generalformula wt% Fe

Akagan6ite hollandite B-FeOOH 62.9 39-60 0.5-19 0.3-5.4 Goethite diaspore a-FeOOH 62.9 41-61 1.0-8.0 <0.2 <0.2 Lepidocrocite boehmite 7-FeOOH 62.9 45-60 0.5-11 Maghemite cubicspinel 7-FerO" 69.9 58-63 0.4-7.0 <0.1

Fe, Mg, Ca, and K, and three adjustable spectrometers elements that were observed in the oxides and foreign set for Ni, P, and Cl, or for Co, Na, and S, operated at mineral grains that were Present. 15 kV and 0.025-mA samplecurrent on brass.Magnetite Akagan6iteis rust colored, and its powder is orangeto and Kakanui hornblende were used for Fe standards(Ja- brownish. It is grayish blue in polished section, is softer rosewichet al., 1980),and syntheticNi-Fe alloys were than maghemite and magnetite, and is often rich in used for the Ni standards. Values for Ni in the oxides shrinkage cracks, like dried mud. It may contain a sig- were correctedby using the uecrc-rv program. nificant content ofadsorbed water, and this is particularly Photographsand additional chemical data by energy- evident when the electron-microprobebeam is kept on a dispersive X-ray analysis were obtained using a Philips spot.Within 2-10 min, 5-10 wto/oHrO may be lost, as is sEM-EDAxoperated at 20-kV acceleratingvoltage. indicated by an increasewith time in Fe counts. In po- Samplesfor X-ray diffraction analyseswere dispersed Iarized light, akagan6iteis microcrystalline, with orange with acetone onto a low-background quartz slide, and to reddish internal reflections that are intermediate be- data were collected with a Scintagautomated diffractom- tween those ofgoethite and lepidocrocite, appearingsub- eter system,operated under the following conditions:0.03" dued like a coke fire in a fireplace. step size,2- ard 4-mm divergentslits, 0.3- and 0.5-mm Akagan6iteis observedin various relationshipsin Ant- receivingslits, Ge detector,CuKa radiation,\ : 1.54091 arctic iron meteorites. It fills corrosion pits 0.5-2 mm A, +S tv, 40 mA, and a 1.0"/min scanrate. across on the surface, and in the interior it loosely ce- ments cracks as a disordered and microcracked oxide' ConnosroN ASSEMBT.AGES Akagan6ite is usually in contact with as yet uncorroded Corrosion assemblageson iron meteoritesthat have so metal, whereasgoethite, maghemite, and lepidocrociteare far been retrieved from Antarctica are much less exten- often found as oxide intergrowths or as coatings on or sive than those that have been observed on many speci- between other oxides. Our data show (Tables 2 and 3) mens found in temperate and tropical environments. that natural akagan6iteis rich in Cl. In a given meteorite Corrosion on the exterior surfacesof those selectedfor oxide, the Cl content may vary from the limit of detection study is typical and normally consistsof a relatively thin (0.1 wto/o)to several weight percent, as analyzed by the layer of oxides, less than I mm thick. More severecor- electron microprobe. There is both a large-scalevariation rosion develops on under-surfaces,in cleavages,or in among different parts of the meteorite and a small-scale fissureswithin the meteorite. variation, for example,within the akagan6ite-goethitefill- Akagan6ite,goethite, lepidocrocite, and maghemite are ing of an extended crack, due to varying proportions of the four minerals that constitute the bulk of the corrosion these two minerals. Most of the Cl is located in the aka- products observed.They are listed in Table 2 by name, gan6ite,whereas a few tenths ofa percent may be present structure type, and generalformula. Also given is the for- in goethite and lepidocrocite. Cl is apparently absent in mula weight percent of Fe and the observed ranges in maghemite (Table 2). weight percent for Fe, Ni, and Cl as determined by elec- The Cl content of akagan6iteis highest near its inter- tron microprobe. Low Fe totals were observedon all four face with metal or in the deep interior when it is a crack of the oxides and are due mainly to the presenceof water filling. In a typical crack filled with akagan6ite,100 pm of hydration and to irregularities of surfacescaused by wide at the surfaceand narrowing to 5 pm at a depth of the presenceofvoids in the oxide. For this reason,ana- l5 mm, Cl rangesfrom 0. I wto/oat the surfaceto 4.9 wto/o lytical data are presentedto no more than two significant near the bottom ofthe crack. The Cl concentrateswhere figures. The oxides also contain Ni in varying amounts corrosion is currently active, and levels of 4-5 wto/oare as a consequenceof derivation from an Fe-Ni alloy. Aka- typical at theselocations. gan6ite contains significant amounts of Cl, and small Lepidocrocite is sometimes observed coating exterior amounts of Cl were occasionallyobserved in goethite and surfacesand in internal cracks. It has clearly been trans- lepidocrocite. ported in solution and deposited as botryoidal layers, or Observationson specificmeteorites are summarized in it forms laminated bands 5-50 pm thick, sometimesen- Table 3. The major and accessoryweathering products veloping foreign particles such as quartz and feldspar are given for each meteorite, along with the range in Ni, grams. Cl, and S for the major product. Also noted are other Although our efforts focus on iron meteorites,we have BUCHWALD AND CLARKE: CORROSION OF Fe-Ni BY AKAGANEITE 6s9

Taele 3. Corrosionproducts and nonmeteoriticminerals on Antarcticiron meteorites

Major oxidecomposition Weatheringproducts Rangein wt% Elementsintroduced Maior Accessory into oxides Foreignminerals ALH A77283 akagan6ite goethite 0.5-5.5 0 7-2.5 nd Ca, K ALH A77289 akagan6ite goethite 1.8-6 0 0.3-3.4 nd Mg, Ca,Al ALH 478252 akagan6ite goethite 1 5-8.5 0.3-5.0 nd Mg, Si quartz,olivine, zeolite ALH A81013 akagan6ite goethite 0.9-4.5 0.7-1.6 0.2-0.7 Al, Mg, Ca, (S) ALH 84165 akagan6ite lepidocrocite 1.8-12 0.4-1.5 0.1-1.9 Ar,K, (S) DRP A78OO9 akagan6ite goethite, lepidocrocite 1.0-5.6 0.8-4.5 0.2-0.5 Si, Ca, Mg, (S) calcite,-quartz EET 83390 akagan6ite goethite, maghemite, 1.0-13 0.3-2.5 0-2.0 Mg, Al, K, (S) lepidocrocite GRO 85201 akaganeite goethite, maghemite, 0.4-12 0.6-2.4 nd Ar,K, Si feldspar lepidocrocite rLD 83500 akagan6ite 1.2-16 0.4-3.0 0-0 4 Mg, Ca, Al, Na, (S) calcite,*quartz NEP642614 akaganeite goethite,maghemite 22-19 0.4-3.6 nd Ca, Mg, Al PGP A77006 goethite akagan6ite,maghemite 1.0-5.0 <0.2

also examined the corrosion of metal particles in potished Conversion in place of chondritic kamacite to akaga- thin sections of a suite of 8 chondritic meteorites from n6ite is illustrated by seu back-scatteredelectron photo- Antarctica. Both H- and L-group meteorites of petro- graphs (Fig. l) and semiquantitative chemical data. In graphic grades4-6 (Van Schmus and Wood, 1967), and specimenEET 82602, a kamacite particle containing ap- ofweathering classesB and C (Lipschutz,1982), are in- proximately 6 wto/oNi is partly converted to akagan6ite cluded. Specimensselected are from the Allan Hills, the (Fig. la). The enclosingsilicates appear not to have been Elephant Moraine, and the Taylor Glacier, and they were disturbed, indicating that akagan6itehas directly replaced collected during the 1976 through 1982 field seasons. kamacite without significant volume change.Assuming Their names, total weights, classifications,their range in that akagan6iteconsists only of Fe, Ni, and Cl, the ana- akagan6itewto/o Cl, Ni, and Na, and their terrestrial ages lyzedarea (Fig. la) contains 5.5 wto/oNi and 3.1 wto/oCl. are given in Table 4. In general the same relationships A more advanced state of weathering, also without dis- betweenoxides and metals developedfor iron meteorites tortion in the silicate relationships, has converted a net- are observed in association with the metal particles in work of kamacite to essentiallyakagan6ite in EET 82604 these stony meteorites. Metal particles are in the milli- (Fig. lb). 420 x 25 pm areaof akagan6itein this asso- meter and smaller size range and constitute varying ciation contained 5.0 wo/o Ni, 4.4 wto/oCl, 0.5 wto/oS, amounts of the specimen.Average metal content for ob- assumingthat it consistedonly of theseelements and Fe. served-fallH-group chondritesis 18 wt0/0,and for L-group These associationssuggest that HrO, Cl , and O, moved chondrites7.4 wto/o(Mason, 1965).A by-productof these through earlier-formed corrosion oxides to react with chondrite studieswas black and white photographsillus- kamacite and that Fe and some of the Ni were removed trating important relationships;photographic equivalents so that the less denseakagan6ite could replace kamacite of iron meteoritesare difrcult to obtain without resortins on an equalvolume basis. to color photography. An akagan6ite-goethitevein penetratinga chondrule in

TABLE4. Akagan6itein associationwith metalgrains in Antarcticchondrites

Akagan6itecompositions Rangein wt% Mass Age.' (kS) Type Weathering cl (103yr)

ALH A76009 407 LO B 0.3-23 2.1-7.4 <0.1 ALH A77OO4 2.2 H4 <02 1.7-4.6 <0.1 170 + 70 ALH 477285 0.3 H6 0.2-1.8 2.7-6.7 <0.1 220 + 70 ALH A79OO2 0.2 HO c 0.3-3.9 194.7 <0.1 EET 82602 1.8 H4 B 0.2-3.3 2.0-5.3 no EET 82604 t.o H5 Btc 0.5-3.2 1.7-5.9 nd EET 82606 1.0 LO B o.4-3.4 1.8-19 nd TYR 82700 0.9 L4 B o642 2.5-5.5 no . Allan Hills(ALH), Elephant Moraine (EET), Taytor Gtacier (TyR). "" Nishiizumi(1984). 660 BUCHWALD AND CLARKE: CORROSION OF Fe-Ni BY AKAGANEITE

Fig. 1. Backscattered-electronimages of akagan6itereplacing metal in polished thin sectionsof Antarctic chondrites. (a) EET 82602 (H4), akagan6ite(gray) replaceskamacite (white). Various silicatessurround the akagan6ite,and a thin akagan6ite-goethite- filled horizontal crack is at the upper right. The lighter gray rectangleat the upper right of the akagan6itefield is an area analyzed by selr-roex. The network of cracksin the akagan6iteis typical. Scalebar: 0.05 mm. (b) EET 82604 (H5), a network of kamacite (white) largely replacedby akagan6ite(gray). Darker minerals are silicates.Scale bar : 0.1 mm.

EET 82602 demonstratesdeposition of these weathering indication of the still distinct boundary of the chlorapa- products by solutions moving into a crack (Fig. 2). A tite having been affected. Clearly demonstrated in this semiquantitative analysis of a l0 x l0 pm area, again associationis the dependenceofakagan6ite composition ignoringHrO and Or, found mainly Fe, 5.5 wto/oNi, 0.9 on the composition of the metal from which it formed. wto/oCl, 0.4 wto/oS, 1.1 wto/oAl, 3.1 wto/oMg, 2.6 wto/oSi, The somewhat thicker akagan6itein the bottom half of and 0.6 wto/oCa, suggestingthat parts of the adjacent Figure 3b formed by replacementof part of the adjacent troilite and silicates were dissolved and incorporated in kamacite field and retains the approximately l8:l Fe:Ni the akagan6ite-goethitefilling. ratio of the kamacite. Analyses in this akagan6itearea Troilite and silicate associationsmay also be invaded were all close to 5 wto/oNi, 90 wto/oFe, and 4 wto/oCl, by akagan6iteveins (Fig. 3a). Analysis indicates that Ni, ignoring HrO and Or. The akagan6itein the top of the Cl, HrO, and possibly Fe were moved along cracks to picture formed from taenite with an entirely different Fe: react with the troilite and silicatesto produce akagan6ite. Ni ratio of about 4:1. Consequently,this akagan6iteis A semiquantitative analysis of a small area, neglecting very rich in Ni, averaging 19 wto/oNi, 76 wto/oFe, and 4 again the light elements,indicated major Fe, 2.9 wto/oNi, wto/oCl, by the same analytical procedure. 4.1 wto/oCl, and 3.0 wto/oS. Growth contours that are readily recognizedunder the microscope in these veins DrscussroN are suggestiveofgrowth by solution transport. An interface between metal and chlorapatite in EET Cl and Ni in akagan6ite 82606 (Fig. 3b) reveals that a thin strip of the metal has Akagan6ite is geologically a rather rare mineral that been replaced by akagan6ite,but there appearsto be no was first describedas a weatheringproduct from the Jap- BUCHWALD AND CLARKE: CORROSION OF Fe-Ni BY AKAGANEITE 66r

Fig.2. Backscattered-electronimages of a chondrule in EET 82602 (H4). (a) A section through a silicate chondrule (dark) partially surroundedby kamacite (white), with slightly weatheredkamacite also in the silicate matrix. A vein of akagan6ite-goethite penetratesthe chondrule from its lower right to the upper left. Thin veins of akagan6ite-goethitealso border the chondrule. Scale bar : 200 pm. (b) Enlargementoflower right area of akagan6ite-goethitevein (white to light gray) penetratingthe chondrule silicates (dark). Scalebar : 10 pm. aneselimonite mine Akagan6(Mackay, 1962). It wasnot- not all of the tunnel sites, making it rather easyfor Cl to ed as a corrosion product on a few iron meteorites by enter or leave the structure. Marvin (1963),who identified it in X-ray powder pho- Akagan6itemay also accommodateNi in its structure. tographs.Akagan6ite (Table 2) has the idealized formula In the present study, up to 19 wt0/oNi was observed, p-FeOOH and has long been known from synthetic work although 3-5 wto/oNi was the normal amount because (Mackay, 1960). most of the akagan6itehas formed from kamacite. Its An important point for corrosion of ferrous metal is X-ray diffraction pattern typically gives broad peaks,un- akagan6ite'sability to host Cl in its structure, synthetic doubtedly as a result of very small crystal size. This is material having been reported to contain from 1.3 to 6.4 consistentwith earlier observations(Mackay, 1962;KeI- wto/oCl (Keller, 1970). Many authors have noted that it ler, 1970) on synthetic akagan6iteby reu (transmission easily adsorbs water, 2-20 wto/o,particularly when crys- electron microscopy) of crystalsaveraging 2500 x 250 A tals are fine or the crystallinity is poor. Synthetic akaga- with a maximum length of 5000 A. It has, therefore, not n6ite has an exchangecapacity, Cl- and OH being rather been possible to identify changesin lattice parameters easilyexchanged. By repeatwashing with water, synthetic due to Fe:Ni ratio variations. The roles of both Cl and akagan6itewith 5.4-6.3 wto/oCl was shownto lose 2l-36 Ni in the akagan6itestructure will be discussedin detail wt0/oof its Cl (Keller, 1970). The unusual properties of elsewhere(J. E. Post and V. F. Buchwald, manuscript in this iron oxide are best accounted for by the formula preparation). proposed by Keller, Fer(O,OH)l,u(Cl,OH)=r,where 8 FeOOH formula units are arrangedin a monoclinic cell Corrosion mechanism as in hollandite (J. E. Post and V. F. Buchwald, manu- The corrosion mechanism of meteoritic metal in the script in preparation) and where Cl occupies some but Antarctic environment is in large part an electrochemical 662 BUCHWALD AND CLARKI: CORROSION OF Fe-Ni BY AKAGANEITE reaction that produces akagan6iteas the initial product. the electrochemicalnature ofthe corrosion reaction, the Sourcesofthe required potential differenceto drive cor- high ionic mobility of Cl-, and the size of the Cl- ion that rosion cellsare the normal componentsof meteoritic metal allows it to fit into the tunnel sites of akagan6iteand and structural cracks.The major phaseis generallykam- stabilize its structure. acite (bcc Fe containing 4-7 wto/o Ni), with minor The electrochemicalrequirement is that anions move amounts of the accessoryminerals taenite (fcc Fe with to the anode, the surfacewhere Feogoes into solution, to 2540 wto/oNi), schreibersite[(Fe,Ni)3P], and troilite (FeS) maintain chargebalance and that electronsflow through providing interfacesof differing chemical potential. These metal to the cathode where anions are produced. Chlo- interfaces,as well as cracks, are sites where O, and elec- ride ions are apparently attracted to the vicinity of the trolytes invade the metal. The result is that anodic kam- corrosion front preferentially, their high ionic mobility acite goesinto solution, electrons pass through metal to undoubtedly being an important contributing factor. At the cathode where O, (and sometimes H*) is reduced, the corrosion front, Cl- decomposesany passivatingiron and akagan6iteprecipitates. It appears that in the Ant- oxide film on the metal surface and often gives rise to arctic deep freeze,such reactionsmay take place without pitting attack. Under these conditions, a Cl-containing liquid water, evidently requiring a much extended time akagan6ite forms and encloses any taenite, troilite, or owing to low coefficientsof diffusion in ice and in oxides. schreibersite located in the corrosion zone as passive In simplest form and using conventional half-reactions, minerals. Only much later in corosion development, a the processmay be expressedas follows. Metal (Feo)is stage rarely observed in Antarctic meteoritic metal, do oxidized at the anode these minerals disintegrate, usually in the order given, schreibersite,being able to survive in the corrosion prod- Feo-Fe2+i2e ucts for a surprisingly long time. and O, is reduced at the cathode Slowly in the Antarctic environment, but more rapidly in temperate climates, Cl in akagan6iteis exchangedwith 02 + 2H2O -t 4e - 4OH-, OH-, and Cl is releasedinto solution to move again to or, alternatively, H is reduced at the cathode the corrosion front or to be flushed from the system.The akagan6ite left behind will approach the composition 2H* + 2e.---."..-.-Hz. [Fe,,Nd[O,r(OH)r0](OH)3and, having lost its Cl, be- Combining the first two equations comesunstable. Under conditions of modest heating and/ or seasonalchanges in temperature and humidity, it de- 2Feo* 02 + 2H'O 2Fe(OH). + 2OH-. ;;;; composesaccording to a reaction such as This is followed under oxidizing conditions by the for- 2[Fe,,Ni][O',(OH),.](OH)3 mation of akagan6ite 77-FerO3+ NiO 2Fe(OH)* + 2OH- ineversible 1- VzO,;;;;2B-Fej.OOH + H,O. maghemite' + l6a-FeooH + Nio + 15H,O,

In order to representthe degradation of meteoritic metal g@thite more realistically, we have adopted a variant of Keller's formula (Keller, 1970) for akagan6ite,[Fe,rNi][O,r- a reaction that may be termed the aging of akagan6ite. (OH)rolClr(OH). It satisfies structural constraints, is in The products, typically maghemite and goethite, may for chargebalance (Fe is assumedto be Fe3+,and Ni is Nir*), as yet unknown reasonsoccur in widely varying propor- and contains 55.9 wto/oFe. 3.9 wto/oNi. and 4.7 wto/oCl- tions. They are intimately intergrown on the micrometer amounts that have beencommonly observedin this study. scale,but may be distinguishedin polished section (mag- The reaction may then be expressedas hemite is brownish and harder and therefore stands out in relief). They contain most or all of the Ni and Fe that 30Feo+ 2Nio + 47O + l9H,O + 4H* + 4Cl- were previously in the akagan6ite. Very little loss by leaching is observed in these early corrosion stages.The kamacite greatterrestrial ageof some of the meteoritesstudied (Ta- -.------: bles I and 4) combined with the limited development of .- 2[Fe''Ni][O,,(OH),0]CI,(OH). ineversible aka€n6i1e aging products when compared with temperateand trop-

This reaction results in the formation of akagan6iteas tIn this work we have observed a cubic spinel that may be a replacement for kamacite. Little Ni or Fe is leached either maghemite (7-FerO3)or magnetite (FerOo).It contains Ni from the corrosion product, and Cl is derived and accu- and has an X-ray difraction pattern that may be interpreted as Ni-substituted maghemite or Ni-substituted mag- mulated, even from present that of either environments where it is in netite. Data are insufrcient to distinguish betweenthe two pos- very low concentrations.Three factors appear to be im- sibilities, so we have labeled all of the observedspinel material portant in explaining this dramatic accumulation of Cl: as maghemite. BUCHWALD AND CLARKE: CORROSION OF Fe-Ni BY AKAGANEITE 663

Fig. 3. Backscattered-elecrronimages of akagan6iteassociations in EET 82606 (L6). (a) Akagan6ite-goethiteveins (dark gray) : through troilite (light gray) and silicates (dar$. Growth contours in akagan6iteare typical of transport reactions. Scalebar 25 pm. (b) Taenite (T) and kamacite (K) in contact with a thin band of akagan6ite(A) invading metal at a previous interface between metal and chlorapatite (C). Scaleas in (a). Seetext for further discussron.

ical occurrences,suggests that aging is much slower in the shown that the metal of iron meteoritescontains little Cl. Antarctic environment. Their neutron-activation analysesshow very low levels of Cl in unweatheredmetal and suggestan upper limit of Sourceof Cl 10 ppm Cl (probably very high). As akagan6itereplaces What is the source of the Cl that plays this important kamacite in approximately equal volumes, Cl must be role in the formation of the corrosion product akagan6ite introduced from some other source to provide the high in Antarctic meteorites? Chlorapatite is the only well- levels that are observed characterizedCl-containing mineral that occurs in iron The mineral lawrencite (FeCl') has a long and contro- meteorites(Buchwald, 1975, 1984).Although chlorapatite versial history that will be treatedin detail elsewhere.The may contain as much as 5 wto/oCl, it is sporadically dis- name has been used commonly in the meteoritic litera- persed in comparatively rare silicate-containing inclu- ture, particularly in referenceto Cl-containing, semiliquid sionsthat could not possibly supply the amount of Cl that effiorescencesassociated with the corrosion of meteoritic is observed. Three other possibilities remain: the metal metal. Jackson(1838) first reported Cl in meteoritesin itself, the mineralogical chimera lawrencite, or introduc- the severelycorroded Lime Creekiron meteorite find. His tion from the terrestrial environment by the mechanism claim that the Cl was indigenous to the meteorite was outlined above. countered promptly in an insightful paper by Shepard Although it is not the interpretation given by Berkey (1842). Jacksonand Hayes (1844) answeredwith what and Fisher (1967), they neverthelesshave persuasively appearsto have beenan overpowering,even ifby modern 664 BUCHWALD AND CLARK-E: CORROSION OF Fe-Ni BY AKAGANEITE eyes largely unresponsive, rebuttal. Later J. Lawrence much current interest. Irregularities in halogen abun- Smith (1855, 1874, 1877)reported observingthe "pro- danceshave been noted in both Antarctic meteoritesand tochloride of iron" in the solid state in the Tazewell and rocks (Dreibus and Wiinke, 1983; Dreibus et al., 1985; Smith's Mountain iron meteorites. Insufficient chemical Heumannet al., 1987).Although our findingsdo not speak and physical data were given to characterizethe material directly to these anomalies, the weathering mechanism with any certainty, but the idea of an iron chloride mineral proposed is an obvious source of Cl contamination for becameaccepted. Daubr6e (1877) introduced the name metal-containing meteorites. Weathering-product akaga- lawrenciteto honor the discoverer,and later Smith (1883) n6ite accumulatesCl, perhaps in part from decomposing used the term himself. The name has been acceptedby chlorapatite in some meteorites,but certainly in the main modern authorities, sometimes with equivocation, and from the local environment. The processapparently has continues to be used despite the lack of even a minimal a high Cl- ion specificity. A highly mobile anion is re- descriptionofnatural material in the literature (Buchwald, quired to provide charge balance at the metal interface, 1977). In the course of this work we have examined a bringing large numbers of Cl- ions to the region of aka- number of dried residues from typical "lawrencite" oc- gan6iteformation. The ionic radius of the Cl- ion fits the currences,and in every casean akagan6iteX-ray diffrac- requirementsfor tunnel-site occupancyin the akagan6ite tion pattem has been obtained (Buchwald and Clarke, structure and is incorporated in it and becomeslocalized. I 988). This ionic selectivity provides a rationale for unexpected The presenceof Cl in iron meteorite finds is real, of halogen-abundancerelationships. Under these circum- course,the older literature having been reviewed by Co- stances,one would not expect to see a relationship be- hen (1903).Recently it hasbeen shown (Buchwald,,1975, tween the seaspray-derived component of the Cl present 1977, 1986\for iron meteoritesfound embeddedin tem- in akagan6iteand Na and K. Interpretations of isotopic perate-zone soils that the Cl is introduced from the data, such as 36Clage determinations, could also be af- groundwater to which these meteorites have been long fected. exposed.During exposure,Cl-along with O, and HrO- decomposesthe Fe alloy. The corrosion mechanism out- Antarctic environmentalfactors lined above expandson this earlier work and explains the The areaswhere Antarctic meteoriteshave been found accumulation of Cl in terms of akagan6ite.Cl accumu- are notoriously stormy. Wind velocities are frequently lation apparently begins as the meteorite lands, and ak- more than 20 m/s, and under thesecircumstances, blow- agan6itecontinues to play a role in corrosion as long as ing mineral grains and ice crystals become mild abra- metal remains. sives.This is probably why we have not yet seenan Ant- Antarctic meteoritesadd a new dimension to this pic- arctic iron meteorite with a heavy corrosion scale. ture, as many of them have never been buried in soil. For Meteorites from temperate latitudes often display coat- example, the Allan Hills meteorites, found on the wind- ings several millimeters to centimeters thick, whereas swept bare ice fields at an altitude of about 2000 m, con- Antarctic iron meteorite coatingsrarely exceedI mm and tain akagan6itewith up to 5.0 wto/oCl. This Cl was ap- are usually only 0.1 mm thick. The severewinds com- parently introduced from the snow and ice ofthe Antarctic bined with corrosive processesin Antarctica produce dis- environment. Unfortunately, Cl analysesof the ice in con- tinctive specimen-surfacemorphologies. Corrosion pref- tact with the meteorites are unavailable, but concentra- erentially attacks kamacite, and since abrasive particles tions may well be in the low ppm range as was found by in due time remove most of the akagan6ite,iron meteor- Heumann et al. (1987) and Mulvaney et al. (1988) for ites often show a pronounced surface relief. On the sur- sea-shelflocations.The annual averagetemperature at the face of Allan Hills 477283, for example, the more resis- oC), Allan Hills is low (-30 and precipitation is low and tant taenite lamellae stand in relief, displaying a delicate difficult to measure.The meteoriteshave presumablyspent Widmanstiitten pattern and revealing the internal octa- most of their residencetime on Earth within the ice, being hedralstructure of the meteorite(Clarke et al., l98l). On eventually exposedby the strong katabatic winds out of Derrick Peak 478009 and other specimensof that fall, the South that remove surface snow and evaporate the the effect is even more dramatic: the large, hard schrei- upper part of the snow and ice fields. The ultimate source bersitecrystals protrude as irregular,bronze-colored knobs of the low levels of Cl in the snow and ice is probably 0.5-5 mm above the rust-colored surface,an effect that largely sea spray from the oceans,with an increment of is unknown from any other iron meteorite(Clarke, 1982b). hydrogen chloride exhalationsfrom volcanic action. The The reason is, no doubt, that the rate ofabrasion due to Cl is carried as either an aerosol or a gas over the snow wind-carried particles is significantly greaterthan the rate and ice f,elds, where a portion is incorporated in newly of corrosion-product accumulation. formed snow and ice deposits(Duce et al., 1973; Heu- The absenceof liquid water becauseof the low Ant- mann et al., 1987;Shaw, 1988).Cl may also be concen- arctic temperaturesis an obvious limitation to corrosion trated in the residual ice surface,being preferentially left development.The meteorites,however, are dark colored, behind as ice sublimes. and they do absorb heat during limited periods of expo- Concernover the ozonelayer, among other reasons,has sure to the Sun's radiation. Specimensfound on the ice made the halogen geochemistry of Antarctica a topic of on sunny days have, on occasion,been observedto be in BUCHWALD AND CLARKE: CORROSION OF Fe-Ni By AKAGANEITE 665

contactwith tiny poolsofwater. Schultz0986) measured for meteorites either buried or exposedare unknown. It the internal temperatureof a stony meteorite lying on the is reasonableto assume,however, that ratesat the surface blue ice surface of the Allan Hills and found that on 2 are higher and that this is where most of the corrosion austral summer days of the 2l the experiment ran, tem- takesplace. peratureswere just above the freezingpoint of water. Our We observed no correlation between the location and observation, mentioned above, of botryoidal lepidocro- the severity of corrosion except for the exposed moun- cite in some corrosion assemblagesstrongly suggeststhat tain-side location for the Derrick Peak specimensmen- liquid water is sometimespresent. Marvin (1980) iden- tioned above. We did note, however, that foreign sub- tified hydrated magnesium carbonates and sulfates in stances were more pronounced on meteorites found white surficial depositson Antarctic stony meteorites.The among rock debris in the mountain rangesthan on those depositswere explainedas formed from saltsleached from from the blue ice fields of the Allan Hills. Some speci- the meteorites by liquid water produced from snow on mens were visibly affectedon the surface,having yellow- sun-warmed meteorite surfaces. ish or whitish incrustations. On such specimens,such as Derrick Peak, Inland Forts, and Purgatory Peak, calcite Introduced elementsand minerals was identified in veinlets and vugs, deposited together As may be seenfrom the last two columns of Table 3, with lepidocrocite or introduced into cracks of akaga- foreign elements and minerals have been incorporated n6ite. The presenceof calcite as crystalline veinlets is fur- into the akagan6itecorrosion assemblages.Even in the ther documentation of the sporadic presenceof liquid interior of the Antarctic ice cap, wind-transported min- water. eral grains from eroded nunataks are apparently ubiqui- tous and may adhere to the corroding meteorite, ulti- CoNcr,usroNs mately to be cementedto it by growing iron oxides. Most Akagan6ite,previously regardedas a rare mineral, is in particles are qvartz, in the l0 to 100-pm range, but oliv- reality a significant corrosion product of the Fe-alloy ine, feldspar, amphibole, and zeolite grains have also phasesin Antarctic meteorites.Work in progresssuggests beenobserved. that it is equally important in the corrosion processof On decomposing, the mineral grains release small metal-bearing meteorites in all environments. Akaga- amounts of A1, Si, Ca, and K, which may become incor- n6ite's particular importance derives from its crystal porated into the growing akagan6iteor into later-forming structure that readily incorporates Cl ions attracted to lepidocrocite. The amounts of these elements are gener- the corrosion front and from its small crystal size that ally low, on the order of a few tenths of 1 wt0/0,but oc- greatly enhancesits water adsorption capacity. Cl- ions casionally, as in Purgatory Peak A77006, the concentra- positioned in the tunnel sites of akagan6iteare readily tions in akagan6itereach l.l wto/oMg and0.2 wto/oAl. S, released under moist conditions to move again to the probably as sulfide, is also presentin akagan6ite,usually akagan6ite-Feointerfaceregion, where they serve to de- in the rangeof 0. l-1.0 wto/0.S hasbeen put in parentheses passivatethe Feoand reinitiate corrosion. Invading aka- in Table 3 becauseit probably is not a foreign ion but gan6ite may again incorporate the Cl ions, providing a may originate from decomposition of troilite in the me- reservoirofcorrosive agentfollowingjust behind the re- teorite. P is sometimes present in akagan6ite,usually in action front. the rangeof 0.1-1.0 wt0/0,but occasionallyreaching the 5 Purer forms of akagan6itetypically contain 4-5 wto/o wto/olevel. This is to be expected,however, as most iron Cl, but, as it is often intergrown with Cl-free goethite on meteoritescontain appreciableamounts of schreibersite. a microscopic scale, microprobe analyses often yietd On penetrating the atmosphere,sulfides and phosphides somewhatlower Cl values (0.34 wto/o).Akagan6ite forms located at the surfacemelt preferentially and solidify to in situ by replacement of metal and contains Ni when very fine grained multicomponent eutecticsin the fusion formed from meteorites. The Ni level reflects the com- crust. These components are the first to be attacked by position of the phase from which it formed, having Fe/ corrosion and are responsible for the occasionalhigh p Ni ratios of about 16 when formed from kamacite and and S concentrationsofakagan6ite in the initial stagesof about 4 when formed from taenite. On aging, akagan6ite corrosion. Later, most of the P and S are leached out if losesCl and decomposesin situ to intimate intergrowths liquid water is available. of goethite and maghemite that retain the Ni of the aka- gan6ite. On a given meteorite, therefore, akagan6itewill Terrestrial age and location be located at the actively corroding interface, while goe- In a generalway, one would expect that the degreeof thite and maghemite will be found nearer the surfaceas weathering reflects the terrestrial age of the meteorite. "dead" oxides. Lepidocrocite is occasionally found "That as this is not the caseis demonstratedby the age de- crusts and fillings, deposited on or in the other oxides terminationsof Nishiizumi (1984)and Nishiizumi er al. after deposition from solution. (1987),given in Tables I and 4. We agreewith Nishi- Cl apparently starts accumulation on meteoritic metal izumi's conclusionthat the terrestrial agein the Antarctic surfacesupon landing. Over time, very small amounts of is a composite of two unknowns, the time buried in the Cl are sufficient to destroy large iron bodies, becauseof ice and the time exposedon the surface.Corrosion rates its quasi-catalyticrole in the corrosion reaction. Our ob- 666 BUCHWALD AND CLARKE: CORROSION OF FC-Ni BY AKAGANEITE

servationsdemonstrate that the Antarctic environment is tionships that might be expected under other circum- sufrciently rich in Cl, be it ultimately from air-borne sea stancesmay not hold where corroded metal is involved. spray or from volcanic action (Antarctica has one active A final conclusion is that the corrosion mechanism volcano, Mount Erebus,on Ross Island), to corrode me- proposed here and developed from studies of Antarctic teoritic metal. Although the Antarctic ice may well con- meteoritic metal has much broader implications for fer- tain Na as well as Cl, it is the anion that is both selectively rous metal corrosion. Work in progressconvinces us that attracted to the metal surface and incorporated into the this mechanism is fundamental to meteoritic metal cor- precipitating akagan6ite.There is no site for the large Na rosion in all environments. Preliminary studies suggest cation in the corrosion products. Precipitating akagan6ite its importance for archeological ferrous metals and for and lepidocrocite may entrap windblown mineral parti- structural metal under some circumstances. cles from eroding mountain ranges.These particles slowly decomposeand provide foreign ions that become in- Acxllowr,nncMENTS corporated in the various corrosion products. We are indebted to the Meteorite Working Group and to Dr. K. Yanai Consideringonly bulk composition, all iron meteorites for providing specimens.J. E. Post, U B. Marvin, B. Mason, J. L Good- would be expectedto be equally susceptibleto corrosion. ing, and E Maahn provided stimulating discussion,and E Olsen a most Variations in structure and their associatedmineralogical helpful review. E. Jarosewich,J. Nelen, and Inger Sondergeardprovided relationshipsare, however, responsiblefor important dif- electron-microprobesupport; J. E. Post, D. Ross and S. Karup-Moller' data; and J Collins, R Johnson, T. Rose, T. Thomas, The electrochemicalpotentials establishedbe- X-ray diflraction ferences. F. Walkup, E Johannsen,and M Ketler, technical support. The work tween kamacite, taenite, schreibersite, and troilite ac- was initiated while V. F. Buchwald was a visiting scientistin the Depart- count for differing levels of corrosive activity. A meteorite ment of Mineral Sciences,National Museum of Natural History, Smith- rich in large-anglegrain boundaries (IIB, IIIA) or in in- sonian Institution, Washington, September 1987 through January 1988' LiebersErickson Fund, Smithsonian clusions (IA) is more exposed to corrosion attack than We are both indebtedto the Suzanne Institution, for partial financial support. homogeneous,coarse-grained meteorites (IIA) or heter- meteorites(IVB). The ogeneous,but inclusion-poorduplex RnrnnrNcns crrno fusion crust on iron meteorites, being largely magnetite, will be noble relative to the bulk meteorite and will en- Berkey, E., and Fisher, D.E. (1967) The abundanceand distribution of et Cosmochimica Acta, 31, hance the attack on metal immediately below the fusion chlorine in iron meteorites. Geochimica I 543-l 558. crust. Although time must be a factor in the amount of Buchwald,V F (1975)Handbook ofiron meteorites,1418 p. UniYersity corrosive activity to which a given specimenis exposed, of Califomia Press,Berkeley, California the complexities of individual residencehistories do not -(1977) The mineralogy of iron meteorites Philosophical Trans- lead to a recognizable correlation between degree of actionsofthe Royal SocietyLondon, 286A,456491- -(1984) Phosphateminerals in meteoritesand lunar rocks. In J.O. weatheringand tenestrial age. Nriaguand P.B.Moore, Eds., Phospbate minerals, p 199-214.Spring- The reason for the alarming breakdown of some me- er-Verlag,New York. teorites in museum collections is that akagan6iteresides - (1986)Jerslev, the first iron meteoritefrom Denmark. Meteoritics, in the interfacesbetween uncorroded metal and inactive 21,47-58. (1988)Akagan6ite, not lawrencite, iron oxides. Moisture provided by ambient humidity Buchwald.V.F. and Clarke,R.S., Jr corrodesAntarctic iron meteorites(abs.). Meteoritics, 23, 261. slowly penetratesthe oxides and reinitiates active corro- Buddhue,J.D (1957)The oxidation and weatheringof meteorites,161 sion under what may appear to be a benign crust. Sud- p University of New Mexico Publicationsin Meteorites,no. 3, Albu- denly, what appearedto be a substantialmeteoritic mass querquerNew Mexico crumbles. Protective measuresinclude flushing Cl from Cassidy,W.A. (1980)Field occurrencesand collectionprocedures. In U.B' B Mason, Eds., Catalog of Antarctic meteorites, 1977- reducing oxygenand humidity levels. There Marvin and the crust and 1978. Smithsonian Contributions to the Earth Sciences,23, 3-7' is no need to resort to the doubtful mineral lawrencite to Clarke, R.S., Jr. (1982a)Description of iron meteorites.In U.B. Marvin explain the corrosion of meteoritic metal. Phenomena and B. Mason, Eds., Catalog of meteorites from Victoria Land, Ant- previously attributed to lawrencite by some authors are arctica, 1978-1980 Smithsonian Contributions to the Earth Sciences, readily explained by the well-characterizedmineral aka- 24,49-56. -(1982b) The Derrick Peak, Antarctica, iron meteorites.Meteorit- gan6ite. ics.17.129-134. The Antarctic meteorites preserve the initial steps in -(1984) Descriptionsof iron meteoritesand mesosiderites.In U B. the degradation of meteorites. Becausethe temperature Marvin and B. Mason, Eds., Field and laboratory investigations of most of the time is far below the freezing point and be- meteoritesfrom Victoria Land, Antarctrca.Smithsonian Contributions to the Earth Sciences,26,49-53. causethe air is very dry, the decomposition of akagan6ite -(1989) Descriptionof iron meteorites.In U.B. Marvin and G.J. to other minerals such as goethite, maghemite, and mag- MacPherson, Eds., Field and laboratory investigationsof meteorites netite is inhibited. The full decomposition of akagan6ite from Victoria Land and the Thiel Mountains region,Antarctica Smith- may, however, be studied on meteorites recovered from sonian Contributions to the Earth Sciences,27,61-64 DE., and Ross,D.R. (1981)An Antarctic more temperate climates. Clarke,R.S., Jr., Appleman, iron meteorite contains preterrestrial impact-produced diamond and The specificity of the Cl accumulation processin metal lonsdaleite.Nature, 29 l, 396-398. corrosion must be consideredin studies that involve Cl Cohen. E (1903) Meteoritenkunde,Heft II 302 p. E. Schweizerbart'sche elemental and isotopic abundances.Geochemical rela- Verlagshandlung,Stuttgart, West Germany' BUCHWALD AND CLARKE: CORROSION OF Fe-Ni BY AKAGANEITE 667

Daubr6e, M. (1877) Observations sur la structure int6rieure d'une des tigations of meteoritesfrom Victoria Land and the Thiel Mountains massesde fer natif d'Ovifak. Comptes Rendus des s6ancesde L'Aca- region, Antarctica. Smithsonian Contributions to the Earth Sciences, d6mie des Sciences.84. 66-70 27, 146p. Dreibus,G, and Wiinke, H. (1983) Halogensin Antarctic meteorites. Marvin U.B., and Mason, B. (1980)Catalog of Antarctic meteorites,1977- Meteoritics,18, 29 l-292. 1978.Smithsonian Contributions to the Earth Sciences,23, 50 p Dreibus,G., Wiinke,H, and Schultz,L. (1985)Mysterious iodine-over- -(1982) Catalogof meteoritesfrom Victoria land, Antarctica, 1978- abundancein Antarctic meteorites.In J.O. Annexstad, L. Schultz,and 1980.Smithsonian Contributions to the Earth Sciences,24,97 p. H. Wiinke, Eds., International workshop on Antarctic meteorites.Lu- -(1984) Field and laboratory investigationsof meteoritesfrom Vic- nar and PlanetaryInstitute Technical Report 86-01, 34-36. toria Land, Antarctica. Smithsonian Contributions to the Earth Sci Duce,R.A , Zoller,W.H., and Moyers,J.L. (1973)Particulate and gaseous ences,26, 134p. halogens in the Antarctic atmosphere Journal of Geophysical Re- Mason,B. (1965)The chemicalcomposition ofolivine-bronzite and oliv- search,78, 7802-78I 1. ine-hypersthenechondrites. American Museum Novitates, no. 2223, Faust,GT, Fahey,J.J, Mason, B.H., and Dwornik, E.J (1973) The p38 disintegration of the Wolf Creek meteorite and the formation of pe- Mulvaney,R., Wolff, E. W., and Oates,K. (1988)Sulphuric acid at grain coraite, the nickel analog of clinochrysotile. U S. Geological Survey boundariesin Antarcticice. Nature. 331.247-249. ProfessionalPaper 384-C. Nishiizumi, K (1984) Cosmic-ray-produced nuclides in Victoria Land Heumann,K.G., Gall, M., and Weiss,H. (1987)Geochemical investi- meteorites In U.B. Marvin and B. Mason, Eds., Field and laboratory gationsto explain iodine-overabundancesin Antarctic meteorites Geo- investigationsof meteoritesfrom Victoria Land, Antarctica Smithson- chimrcaet CosmochimicaActa, 51, 2541-2547 ian Contributionsto the Earth Sciences,26, 105-109. Jackson, C.T. (1838) Chemical analysis of meteoritic iron, from Clai- Nishiizumi, K, Amold, J.R , Elmore, D., Kubik, P.W, Klein, J , and borne, Clarke Co., Alabama. American Joumal of Science,34, 332- Middleton, R. (1987) Terrestrial agesof Antarctic and Greenland me- JJ I. teorites (abs.).Meteoitics, 22, 473. Jackson,C T., and Hayes,A.A. (1844)Remarks on the Alabamameteor- Schultz, L. (1986) Allende in Antarctica: Temperaturesin Antarctic me- itic iron, with a chemical analysisof the drops of green liquid which teontes(abs ). Meteoritics,21, 505. exudefrom it. AmericanJoumal ofScience,48, 145-156. Shaw,G E. (1988)Antarctic aerosols: A review.Reviews ofGeophysics, Jarosewich,E., Nelen,J.A., and Norberg,J A (1980)Reference samples 26.89-r12. for electron microprobe analyses.Geostandards Newsletter, 4,4347. Shepard,C.U. (1842) Analysis of a meteoric iron from Cocke County, Kamp, P.JJ., and Lowe, D.J. (1982)Geology and terrestrialage of the Tennessee,with some remarks on chlorine in meteoric iron masses. Derrick Peak meteorite occurrence,Antarctica. Meteoritics, 17, 119- American Journal of Science,43, 354-363. tz'7 Smith, JL. (1855)A descriptionof five new meteoricirons, with some Keller, Paul. ( I 970) Eigenschaftenvon (Cl,F,OH) .rFer(O,OH),uund Aka- theoretical considerationson the origin of meteorites based on their gan6it NeuesJahrbuch fiir Mineralogie Abhandlungen, ll3,2949 chemical and physical characters.American Journal of Science, 19, King, TVV., Score,R., Gabel, E.M., and Mason, B. (1980)Meteorite I 53-163 descnptions.In U.B. Marvin and B. Mason, Eds , Catalogof Antarctic - (1874) Meteoric iron of Howard County, Indiana. American Jour- meteorites. 1977-1978 Smithsonian Contributrons to the Earth Sci- nal of Science,7,391-395 ences,23.l2-44. - (l 877) Examination ofthe Waconda meteoric stone,Bates County Kracher,A., Willis, J., and Wasson,J.T (1980)Chemical classification meteoric iron, and Rockingham County meteoric iron American Jour- of iron meteorites-Ix. A new group (IIF), revision of IAB and IIICD, nal of Science.13.211-214 and data on 57 additional irons Geochimica et Cosmochimica Acta, -(1883) On the peculiar concretions occurring in meteoric irons. 44,773-787 AmericanJoumal of Science,25, 417-423. Lipschutz,M.E. (1982)Weathering effects in Antarctic meteorites.In U.B. Van Schmus,W R., and Wood, J A. (1967)A chemical-petrologicclas- Marvin and B. Mason, Eds, Catalogof meteoritesfrom Victoria Land, sification of the chondritic meteorites Geochimica et Cosmochimica Antarctica. 1978-1980 Smithsonian Contributions to the Earth Sci- Acra.3l.747-765. ences.24. 6'7-69. White, J S., Jr., Henderson,E.P., and Mason, B. (1967)Secondary min- Mackay, A L (1960) B-Ferric oxyhydroxide. Mineralogical Magazine,32, erals produced by weatheringof the Wolf Creek meteorite. American 545-557. Mineralogist,52, | 190-1197. - (1962) B-Ferric oxyhydroxide-akagan6ite.Mineralogrcal Maga- Yanai, K. (1976) Searchand collection ofYamato meteorites,Antarctica, zine,33, 270-280. in October and November 1974. Antarctic Record, 56, 70-81. Marvin, U B. (1963)Mineralogy ofthe oxidationproducts ofthe Sputnik Yoshida,M., Ando, H., and Omoto, K. (1971)Discovery of meteorites 4 fragment and of iron meteorites Journal of Geophysical Research, near Yamato Mountains, East Antarctica. Antarctic Record, 39, 62- 68, 5059-5068. 65. -(1980) Magnesium carbonateand magnesiumsulfate deposits on antarctic meleorites.Antarctic Joumal, 15, 54-55 MlNuscnrpr RECETvEDMencs 23, 1988 Marvin, U.B., and MacPherson,G J. (1989)Field and laboratoryinves- Menuscnrpr AccEprEDJntuenv 19. 1989