elements m meteoritic minerals - smithsonian institution

SMITHSONIAN CONTRIBUTIONS TO THEEARTH SCIENCES

NUMBER 3

Brian Mason Minor and Traceand A. L. Graham p i t

Elements mMeteoriticMinerals

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

1970

ABSTRACT

Mason, Brian and A. L. Graham. Minor and Trace Elements in Meteoritic Minerals.Smithsonian Contributions to the Earth Sciences, 3:1—17. 1970.—Nickel-iron,

troilite, olivine, pyroxenes, plagioclase, chromite, and phosphate minerals (chlor-apatite and/or merrillite) have been separated from a number of meteorites (Modoc,St. Severin, Winona, Haraiya, Marjalahti, Springwater, Johnstown, Mt. Egerton,Soroti) and analyzed for minor and trace elements with the spark-source massspectrometer. The elements Ni, Go, Ge, As, Ru, Rh, Pd, Sn, Sb, W, Re, Os, Ir, Pt,and Au are concentrated in nickel-iron: Se and Ag in troilite; Th, U, and thelanthanides in the phosphate minerals and in diopside; Eu, Sr, Ba, Rb, and Gs inplagioclase. Molybdenum and tellurium are concentrated in nickel-iron and troilite.The elements Ti, Sc, V, Cu, Zn, Mn, and Ga are distributed over several coexistingminerals.

Official publication date is handstamped in a limited number of initial copies and is recordedin the Institution's annual report, Smithsonian Year.

UNITED STATES GOVERNMENT PRINTING OFFICEWASHINGTON : 1970

For sale by the Superintendent of Documents, U.S. Government Printing OfficeWashington, D.C. 20402 - Price 30 cents (paper cover)

Brian Masonand A. L. Graham

Minor and TraceElements inMeteoriticMinerals

Introduction

During the past decade a very large amount of datahas been accumulated on the abundances of minor andtrace elements in meteorites, and adequate informa-tion is now available on abundance levels of practicallyall elements for the different classes of meteorite. Thedistribution of these elements, however, among the in-dividual phases (minerals) of the meteorites is less wellknown. This can be ascribed in part to the unavail-ability of large enough samples of many meteorites(especially of the rarer classes) for mineral separation,and in part to the difficulty of making clean separationsof the fine-grained minerals in many meteorites, par-ticularly the chondrites. The chondrites are, of course,of special interest, since they represent the least frac-tionated group of meteorites, and contain many minorand trace elements in amounts comparable to solarabundances.

Some significant information has been obtained bythe analysis of magnetic (e.g., metallic) and nonmag-netic (e.g., sulfide plus silicate) fractions of chon-dritic meteorites (see, for example, Onishi andSandell (1956), Wardani (1957), Shima (1964),Fouche and Smales (1967). This procedure, however,is useful only for distinguishing the extremely sidero-phile elements, and provides no information on the dis-tribution of the other elements within the individualminerals. Refined techniques of selective solution ofthe different phases have been applied to chondrites by

Brian Mason, Department of Mineral Sciences, National Mu-seum of Natural History, Smithsonian Institution, Washing-ton, D.C. 20560. A. L. Graham, Department of Geophysicsand Geochemistry, The Australian National University, Can-berra, Australian Capital Territory, 2600.

Vilcsek and Wanke (1965) and Honda and Shima(1967) ; however, study of their results indicates thatthis selective solution is seldom completely quantitative.Moss et al. (1967) have developed a selective decom-position procedure, based on heating a meteoritesample in a stream of dry chlorine, which enablesmeasurement of a number of elements in metal, sulfide,and silicate phases.

The introduction of the electron-beam microprobehas made it possible to measure the concentration ofmany elements in the individual minerals in a polishedsection of a meteorite, without the necessity of sepa-rating the individual minerals by physical or chemicaltechniques. However, the lower detection limit of themicroprobe is about 100 ppm, whereas comparativelyfew elements are present in the common minerals ofmeteorites above that level.

The spark source mass spectrometer appears to bean excellent tool with which to attack this problem. Itis extremely versatile, being capable of detecting allelements from boron to uranium at concentrations ofthe order of 0.1 ppm, and considerably less for someelements. Sample requirements are comparativelysmall: 100 mg is a convenient amount, but good resultscan be obtained on samples of 10-20 mg. This is veryadvantageous for chondritic meteorites, in which manyelements are concentrated in phases such as phosphates(apatite and/or merrillite) and chromite, present inamounts of less than 1 percent of the bulk meteorite.

Experimental

MINERAL SEPARATION.—As originally planned, theprincipal objective of this research was to obtain com-prehensive data on the distribution of minor and trace

1

SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

elements among the minerals of the common chon-drites. Preliminary experiments showed that to obtainadequate samples of accessory minerals such as chro-mite and the phosphates it would be necessary to startwith about 100 g of the meteorite. This limited the se-lection to chondrites available in considerable amounts.Since terrestrial weathering would be a complicatingfactor, only fresh falls were considered. Ultimately twowere selected from the meteorite collection of theSmithsonian Institution, Modoc (NMNH 360), ahypersthene chondrite belonging to the L6 group ofVan Schmus and Wood (1967), and St. Severin(NMNH 2608), a hypersthene chondrite (amphoter-ite subclass) belonging to the LL6 group. General de-scriptions of these meteorites, with bulk analyses, havebeen published: Modoc (Mason and Wiik, 1967) ; St.Severin (Jarosewich and Mason, 1969).

A crust-free piece weighing about 100 g was cut fromeach of these meteorites. The pieces were broken intosmaller fragments which were carefully crushed in ahardened steel mortar until all the material passedthrough a 10-mesh sieve. Further crushing in a largeagate mortar reduced all the material to —100 mesh,except for coarse metal particles, which were removedwith a hand magnet. We found the optimum size formineral separation was the —200 +325 mesh fraction,except for the metal, most of which was coarser than200 mesh, and for which the —100 +200 fraction wasused.

The —200 +325 fraction was sedimented in alarge beaker with distilled water to remove dust. Metal-lic particles were removed with a magnet from thedried fraction, after which this fraction was separatedinto two portions by centrifuging in pure CH2I2

(D = 3.32). The denser portion consisted largely ofolivine and pyroxene, with minor amounts of troiliteand chromite; the less dense portion contained theplagioclase and phosphate minerals; both portions stillcontained a considerable quantity of composite grains.

Pure plagioclase was obtained by extracting a frac-tion with D<2.70 (centrifugation in CH2I2-acetonemixture), purification of this fraction with the FrantzIsodynamic Separator, and boiling the final separatein HC1 to remove any adhering acid-soluble minerals.

The phosphate minerals were concentrated in thefraction with D = 3.08-3.20, followed by passagethrough the isodynamic separator at full power, thephosphate being entirely nonmagnetic. Only smallsamples of about 20 mg each were recovered.

The portion with D>3.32 was further fractionatedusing Clerici solution of controlled density. Hyper-sthene concentrated in the 3.32-3.45 fraction, olivinein the 3.50-3.60 fraction; chromite and troilite formedthe fraction with D>4.0. These fractions were fur-ther processed with the isodynamic separator, yieldingreasonably pure separates of hypersthene, olivine,troilite, and chromite. The hypersthene and chromitefractions were further treated with hot HC1 to removeany adhering olivine and troilite.

The 100-200 mesh magnetic fraction, consisting ofmetal particles with adhering silicates, was placed ina beaker of acetone and agitated repeatedly in anultrasonic cleaner. The silicates were separated fromthe metal by magnetic separation (Modoc), and bycentrifugation in Clerici solution (St. Severin).

The purity of these mineral separates was evaluatedby microscopic examination. The Modoc fractions wereuniformly purer than those from St. Severin, this beingconditioned by the somewhat coarser crystallinity ofModoc. Notes on the individual minerals follow.

Modoc olivine: about 99 percent pure; impuritymainly pyroxene; some grains contain minute opaqueinclusions, probably chromite; slight limonite stainingon many grains.

Modoc hypersthene: about 98 percent pure; im-purities are tiny inclusions of plagioclase and admixedgrains of diopside.

Modoc feldspar: about 99 percent pure; principalimpurity is pyroxene, as tiny inclusions; a few grainsshow a small amount of opaque dust, probablychromite.

Modoc troilite: about 98 percent pure, impuritiesare olivine and pyroxene.

Modoc chromite: about 99 percent pure; impurityis mainly pyroxene.

Modoc metal: about 95 percent pure; principalimpurities are olivine and pyroxene.

Modoc phosphate: about 99 percent pure; impuri-ties are tiny inclusions of olivine, pyroxene, andplagioclase.

The impurities in the St. Severin separates wereessentially the same as the corresponding Modoc sepa-rates, but the estimated purity was lower, viz, olivine,97 percent; hypersthene, 95 percent; feldspar, 96 per-cent; troilite, 94 percent; chromite, 98 percent; metal,90 percent; phosphate, 98 percent.

In order to provide comparative material from otherclasses of meteorites, the following mineral concen-

NUMBER 3

trates were prepared from the meteorites listed, usingtechniques similar to those described above:

Olivine: Marjalahti (Fa12), Springwater (Fa18).Orthopyroxene: Winona (Fs(!), Johnstown (Fs27),

Mt. Egerton (Fs0).Diopside: Winona.Pigeonite: Haraiya.Plagioclase: Winona (An™), Haraiya (An90).Troilite: Soroti.Marjalahti and Springwater are pallasites, Johns-

town a hypersthene achondrite, Mt. Egerton an en-statite achondrite, Haraiya a eucrite, Soroti a troilite-rich iron. Winona is a peculiar meteorite, havingchondritic composition but lacking chondritic struc-ture (Mason and Jarosewich, 1967).

To provide a comparison with terrestrial minerals,olivine, orthopyroxene, and diopside were separatedfrom a peridotite xenolith in a basalt at Camperdown,Victoria, Australia.

ANALYSIS WITH THE SPARK-SOURCE MASS SPEC-

TROMETER. The mass spectrograph used was the M.S.7,manufactured by Associated Electrical Industries Ltd.(now GEC-Elliott Automation). It utilizes doublefocusing geometry for the ion path and photographicrecording of the mass spectrum. The ion source is apulsed R.F. spark passed between two electrodes, whichhave been pressed from a 50:50 mixture of samplepowder and a graphite/Lu2O3 mix. The ion path ismaintained at a vacuum of the order of 10~8 torr, ashigher pressures cause excessive background on thephotoplates.

Each mineral separate was ground in an agatemortar until further grinding had no appreciableeffect upon the degree of subdivision of the material.Sample homogeneity is one of the major problemswhen using this analytical technique. The sensitivityof the method is such that a weight of sample of about0.1 mg is burnt during each analysis and it must betruly homogeneous. Nicholls et al. (1967) fused thesample with a flux to achieve a satisfactory degree ofhomogeneity. In this study we were dealing with sili-cate, sulfide, and metal phases and fusion of themeteorite fractions was not feasible owing to theimmiscibility of the sulfide and the metal phases withsilicate fluxes.

Following Taylor (1965), the finely ground sampleswere mixed with an equal weight of graphite/Lu2O3

mix. The lutetium oxide was present in the graphiteat 50 ppm by weight Lu2O3 and was the internal

standard in the analysis. The geochemical standardsGl and Wl were each equally mixed with the samegraphite/Lu2O3 mix and sparked under identical con-ditions. The mass spectrum for each sample wasrecorded on an Ilford 02 photoplate which wassubsequently processed in accordance with the manu-facturers' instructions. Fifteen exposures were takenon each plate and exposure was measured in units ofcharge, as, owing to the fluctuations of the intensityof the ion beam, a fixed time may not give a consistentexposure. The normal procedure when sparking asample for an exposure range of 1:1000 was for thespark parameters, the repetition rate and length, to bevaried such that the recording devices were operatedunder their optimum conditions. Unfortunately,changing the sparking conditions produces a changein the relative sensitivities of the elements. To avoidthis the conditions of the R.F. discharge of the sparkwere kept constant, the ion beam being attenuatedwhen necessary by the use of an electrical "chopping"device.

The intensity of the lines used for analysis wasread on a Jarrall-Ash microphotometer. These inten-sities were plotted against exposure, and the exposurerequired to produce a line of a given, fixed intensitywas read from this curve. The lutetium 175 line wasused as the internal standard and the exposure re-quired to produce the same given intensity was readfrom a similarly plotted curve. From the standardplates of Gl and Wl, graphs were drawn of ppm

against where Ex is the exposure required toE175

produce a line of given intensity for the isotope X.El75 is the exposure required to produce a line of thesame given intensity for 175Lu.

For each sample Ex and El75 were found by read-ing the photoplate and plotting the intensities againstexposure. The concentration of the element of whichX is an isotope was then determined from the graphsrelating to ppm X produced from the Gl and Wl

Hi A / *j

standard plates. Table 1 gives the mass lines used forthe estimation of each element reported here.

The detection limit is fixed by the length of exposureof the plate to the ion beam produced from thesample, and also by the proportion of the element inquestion that is present as the isotope whose lineintensity is measured in the analysis. If 20 percent of


TABLE

Element

BFClScTiVCrMnCoNiCuZnGaGeAsBrRbSrYZrNbMo

1.—Mass lines used for element

Mass lines

11193545475153555962

63,6566,6769,71

74757985

86,8889

90,9193

95,98

Element

SnSbCsBaLaCePrNdSmEnGdTbDyHoErT mYbHfPbThU

estimation

Mass lines

117, 118123133

135, 137, 138139140141

143, 146147, 149151, 153

155, 157, 158159

161, 163165

166, 167169

172, 173, 174177, 178, 179

208232238

TABLE 2.—Element abundances used as standards

[ppm by weight]

an element X is present as one isotope, and thisisotope is used in the determination of the concentra-tion of X, for a given exposure the detection limit ofX is five times that of a second element Y which hasonly one isotope. In this work, the detection limit wasset at approximately 0.1 ppm atomic for mono-isotopicelements, i.e., the exposure range selected was be-tween 0.1.10"9 and 100.10"9 coulombs.

The accuracy of the figures are dependent upon thevalues accepted for the geochemical standards usedfor calibration, and upon the purity of the mineralseparates. The latter has been discussed already andthe values used for standardization are given in Table2. One plate was run for each sample and the fifteengraded exposures on each plate gave four or five pointson the intensity/exposure graph. The resulting pre-cision is of the order of ± 20 percent.

Elemental Abundances in Separated Minerals

Boron: This element is present in measurableamounts in the feldspar (f) and olivine (o) separates,as follows (in ppm) : Modoc, 2(f) 3(o) ; St. Sever-in,3(f) 2(o) ; Winona, 5(f); Haraiya, 2(f); Marjalahti,

Element

BFClScTiVCrMnCoNiCuZnGaGeAsRbSrYZrNb

Gl

1.5700100

2.81,560

1520

2302.31.2

1345191. 10.7

220260

13210

21

Wl

12200200

346,400

250115

1,3004575

11583161.72.4

22180269510

Element

MoCsBaLaCePrNdSmEuGdTbDyHoErT mYbHfPbThU

Gl

7.51.5

1,0501001701755

9.01.46.90.705.30.501.40.201.06.0

4950

3.2

Wl

0.80.90

16011.920

3.512.53.41. 13.00.604.00.802.080.282. 12.082.20.5

0.5 (o); Springwater, 3(o). Thus, in meteorites mostof this element evidently resides in the feldspar andolivine, as might be predicted from the occurrence ofthe the boron analogs of these minerals reedmergnerite(NaBSI3O8) andsinhalite (MgAlBO4).

Fluorine: This element cannot be measured at thelow concentrations present in most meteoritic minerals,due to interference from iron (1/3 Fe57). In the phos-phate concentrates Modoc contained 880 ppm, St.Severin 36 ppm; this remarkable contrast is evidentlydue to the presence of apatite in the Modoc phosphateand its practical absence in St. Severin.

Chlorine: Chlorine is a major constituent of theModoc phosphate, the amount being too great to meas-ure with the mass spectrometer. Assuming the compo-sition of chondritic apatite given by Van Schmus andRibbe (1969), then from the 880 ppm F the amountof chlorine in the Modoc phosphate would be 1.2 per-cent, and this would contribute 60 ppm to the bulkmeteorite. St. Severin phosphate contains only 130ppm, reflecting the practical absence of apatite.Chlorine was measured in the metal phases (Modoc,74 ppm, St. Severin, 52 ppm), suggesting the presenceof occluded lawrencite (Fe, Ni) Cl2. It was also foundin the troilite (Modoc, 13 ppm; St. Severin, 29 ppm;

NUMBER 3

Soroti, 39 ppm). It was not detected in olivine; in theremaining separates the use of HC1 during separationintroduced possible contamination.

Scandium: This element was detected in all thephases (Table 3), but the small amount in the metalcan probably be ascribed to silicate contamination.Scandium is essentially lithophile, but shows some chal-cophile affinity. In stony meteorites most of this ele-ment is contained in the pyroxenes, but the plagioclaseand olivine also carry a moderate proportion of thetotal scandium. Although the abundances in the indi-vidual phases of the two chondrites are generally com-parable, the variation between specific minerals in thetwo chondrites is greater than expected, and the sum ofthe amounts in the individual minerals from St. Severinexceeds the amount measured in a bulk sample of this

meteorite. The figures for the Camperdown mineralsare similar to those for the meteoritic minerals.

Titanium: This element was detected in all thephases (Table 4). However, the high concentration inchromite and the possible presence of ilmenite meansthat even slight contamination by these minerals inthe separates will greatly enhance the titanium figures.Contamination is probably responsible for the highand variable figures for plagioclase. Corlett and Ribbe(1967) did not detect Ti at the 100 ppm level inmicroprobe analyses of terrestrial plagioclases in theAno_3o and AnGO-ioo composition ranges. However, itcan be concluded from Table 4 that the major fractionof titanium in meteorites is contained in pyroxenes;meteoritic pyroxenes contain more titanium thanpyroxenes in the terrestrial peridotite from Camper-

TABLE 3.—Scandium {ppm)

Meteorite Metal Troilite Olivine Ortho- Clino- Plagioclase Chromite Phosphatepyroxene pyroxene i

Bulk

CamperdownModocSt. Severin. .WinonaHaraiyaMarjalahti...Springwater.Johnstown...Mt. Egerton.Soroti

10.5 19

839

33

13103617

64

5040

6171612

22

4430

2 8. 19

23

10

JIn this and succeeding tables clinopyroxene is diopside inCamperdown and Winona, pigeonite in Haraiya.

2Schmittetal. (1964).

TABLE 4.—Titanium (ppm)

Meteorite Metal Troilite Olivine Ortho- Clino- Plagioclase Chromite Phosphatepyroxene pyroxene

Bulk


1 <501 <50

5050

140100220

4640

3502 1, 0002 1, 0002 1, 200

1,200

120

1,

2 3,2 2,

000

800100

360650200340

» 17,0003 19, 000

2, 100

1,200

700650

4 840

22

1 Jarosewich (unpublished).2 Microprobe analysis.

3 Bunch et al. (1967).* Mason and Jarosewich (1967).


down. The titanium figures for the Modoc and St.Severin troilites are about half those determined by-Moss et al. (1967) in troilite from three hypersthenechondrites.

Vanadium: Bunch et al. (1967) showed that muchof the vanadium in chondrites is contained in thechromite, and this has been confirmed in our study(Table 5). Contamination by chromite may be re-sponsible for the vanadium recorded in the metal andtroilite separates. Clearly the principal carriers ofvanadium, apart from chromite, are the pyroxenes,clinopyroxene being richer in this element than ortho-pyroxene. The contents in the minerals of the ter-restrial peridotite from Camperdown are comparablewith those for the meteoritic minerals. The low contentin the Mt. Egerton pyroxene reflects the chalcophile

character of vanadium under the extremely reducingconditions of the enstatite achondrites.

Chromium: Possible contamination with chromiteis a serious problem, since 0.1 percent of this mineralwill add about 370 ppm Cr to any mineral separate.Many of the data in Table 6 may be too high on thisaccount. The figures for troilite, however, are con-sistent with those published for iron meteorites andtroilite nodules. Smith (1966) reported microprobeanalyses for olivine from the Huckitta pallasite (330ppm), and for olivine from Marjalahti (700 ppm) ; thelatter figure is much higher than our figure. The con-trast between the pyroxenes from Modoc and St.Severin may be of real significance and not due to in-clusions; Modoc is notably rich in chromite, and there-fore its pyroxene may be impoverished in this element.

TABLE 5.—Vanadium (ppm)


Bulk

CamperdownModocSt. Severin...WinonaHaraiya. . . .Marjalahti...Springwater.Johnstown...Mt. Egerton.Soroti

45

9914

1023

554012033

1201

310

10074

123059

i 4, 000i 4, 000

512 54

Bunch et al. (1967).

TABLE 6.—Chromium (ppm)

Meteorite Metal Troilite Olivine Ortho- Clino- Plagioclase Chromite Phosphatepyroxene pyroxene {percent)

Bulk


2 < 1 02 <10

140270

370350330

180270

i 2, 800!800^00

1 1, 000

< 5, 60080

i 9, 0001 4, 1001 4, 3001 4, 8001 1, 900

3701,000140100

3738

340210

3 3, 800* 3, 900s 2, 000

730

1 Microprobe analysis.2 Jarosewich (unpublished).3 Mason and Wiik (1967).

4 Jarosewich and Mason (1969).5 Mason and Jarosewich (1967).e Mason (1963a).

NUMBER 3

The factors controlling the distribution of chromiumbetween chromite and pyroxene remain to be eluci-dated. The low content in the Mt. Egerton enstatitereflects the highly reduced state of this meteorite, andis in agreement with the microprobe data of Reid andCohen (1967).

Manganese: The data in Table 7 were obtainedpartly by the microprobe, for concentrations above1000 ppm, and by the mass spectrometer for lowerconcentrations. The results show that in the ordinarychondrites this element is present in approximatelyequal amounts in olivine and pyroxene, at the 3000ppm level. The low figure for the Mt. Egerton

enstatite is characteristic of this mineral from enstatiteachondrites and enstatite chondrites. Terrestrial min-erals from the Gamperdown peridotite have lowermanganese contents than those from chondrites.

Cobalt: Over 99 percent of this element in stonymeteorites is contained in the nickel-iron, so even aslight contamination of the other phases with metalwill add considerably to their cobalt content. This isprobably responsible for some of the erratic figures inTable 8, especially the high content in Modoc phos-phate, and the somewhat higher content in St. Severinsilicates compared to those from Modoc. Cobalt wasdetected in all phases except the Mt. Egerton enstatite.

TABLE 7.—Manganese {ppm)


Bulk

CamperdownModocSt. Severin...WinonaHaraiyaMarjalahti...Springwater.Johnstown...Mt. Egerton.Soroti

2<102<10

150290

1 3, 600i 3, 200

2,2002,600

* 3, 6001 2, 9001 2, 000

3, 900» 150

1 600i 2, 000i 1, 900i 1, 4001 7,400

230220300320

3 6, 0002 5, 000

580520

* 2, 600« 2, 500« 1. 940

860

1 Microprobe analysis.2 Jarosewich (unpublished).3 Bunch et al. (1967).* Mason and Wiik (1967).5 Jarosewich and Mason (1969).

6 Mason and Jarosewich (1967).7 Mason (1963b).8 Mason (1963a).» Reid and Bohen (1967).

Meteorite

CamperdownModocSt. SeverinWinona. . . . •HaraiyaMarjalahtiSpringwaterJohnstownMt. EgertonSorot

Metal

i 10, 0002 12,000

Troilite

5840

42

TABLE {

Olivine

2102545

724

3.—Cobalt

Ortho-pyroxene

507

193

11n.d.

(Ppm)

Clino-pyroxene

28

109

Plagioclase

161

1

Chromite

CO

C

OC

M

CO

Phosphate

62034

Bulk

18002 4003 400

1 Mason and Wiik (1967).2 Jarosewich and Mason (1969).

380-526 O—70 2

3 Mason and Jarosewich (1967).

8 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

It is more concentrated in olivine than pyroxene,which agrees with data from terrestrial minerals.Terrestrial minerals, however, normally contain a con-siderably higher cobalt concentration than meteoriticminerals, and this is illustrated by the figures for theminerals from the Camperdown peridotite.

Nickel: The distribution of this element (Table 9)closely resembles that of cobalt, and the same re-marks concerning contamination problems apply. Bothtroilite and olivine contain appreciable amounts ofnickel. The figures for troilite agree with unpublishedanalyses of the same samples by E. Jarosewich: Modoc,860 ppm; St. Severin, 760 ppm; Soroti, 510 ppm.Pyroxene contains much less nickel than olivine. Theconsistently higher figures for nickel in the pyroxene,plagioclase, and chromite separates from St. Severinsuggest that these separates are slightly contaminated

with the metal phase. Nickel could not be measuredin the phosphate separates because of a concurrentphosphorus line (2 x P31). Terrestrial olivine, ortho-pyroxene, and clinopyroxene from the Camperdownperidotite show about ten times the nickel concentra-tion of the corresponding meteoritic minerals.

Copper: Hey and Easton (1968) have recentlystudied the distribution of this element in chondritesby selective decomposition of the different phases.They found 22-65 ppm in kamacite, 1610-2610 ppmin taenite, 1-114 ppm in troilite, 17.8-41.5 ppm inolivine, 6.0-22.3 ppm in pyroxene (plus plagioclase).Our results (Table 10) are in good agreement withthese values, although the somewhat erratic figures fortroilite and chromite suggest the presence of sporadicgrains of native copper. The high figure for St. Severinmetal reflects the fact that the nickel-iron in this

TABLE 9.—Nickel {ppm)

Meteorite Metal. Troilite(percent)

Olivine Ortho- Clino- Plagioclase Chromite Phosphatepyroxene pyroxene

Bulk

CamperdownModocSt. Severin. .WinonaHaraiyaMarjalahti. .Springwater.Johnstown...Mt. Egerton.Soroti

14.926.8

820910

2,000230290

34110

63046

19034

* 10n.d.

310

1320

<207427

<20

20 conflict J 13,000410 conflict 2 10,500

3 12, 000

570

1 Mason and Wiik (1967).2 Jarosewich and Mason (1969).

3 Mason and Jarosewich (1967).* Mason (1963a).

Meteorite

CamperdownModocSt. SeverinWinonaHaraiyaMarjalahtiSpringwaterJohnstownMt. EgertonSoroti

Metal Troilite

620 2201,900 64

130

TABLE

Olivine

71414

34

10.—Copper (ppm)

Ortho-pyroxene

37

1013

91

Clino-pyroxene

4

835

Plagioclase

5107

16

Chromite

46021

Phosphate

5220

Bulk

17071

NUMBER 3

meteorite is entirely taenite, whereas that in Modoc isa mixture of kamacite and taenite. Our figures for thesilicates are comparable with theirs, although we findsomewhat less in olivine than they did. Pallasite olivineand achondrite orthopyroxene contain less copper thanthese minerals in chondrites. Terrestrial olivine, ortho-pyroxene, and clinopyroxene from Camperdown con-tain less copper than these minerals from chondrites.

Zinc: The data are presented in Table 11. Zinc wasnot detected in the metal phases. In the analyses of thetroilite the Zn6G line could not be utilized, because ofconflict with 2 x S33, and the Zn67 line was absent (anisotope of low abundance); Nishimura and Sandell(1964) report 10±5 ppm Zn in troilite from chon-drites, which would be consistent with our data. Zincis distributed in all the oxidic phases. Chromite maycontain a high concentration, as in St. Severin; Bunchet al. (1967) report about 1.1 percent ZnO in onechondritic chromite, that from Pultusk. In the silicates

zinc is about equally concentrated in olivine and pyrox-ene, with comparatively little in plagioclase. Zinc isvery low in pallasite olivine, and in achondrite ortho-pyroxene.

Gallium: This element was measurable in all theseparates except the Mt. Egerton enstatite and theSoroti troilite (Table 12). It is notable for being de-tectable in all phases, but is concentrated in the metal,plagioclase, and chromite. However, the plagioclase inWinona and especially Haraiya is notably depleted incomparison to the chondrite plagioclases. The lowercontent in metal from St. Severin may be related tothe somewhat higher degree of oxidation of this mete-orite compared to Modoc. The figures obtained areconsistent with those reported by Moss et al. (1967)and Fouche and Smales (1967) for other chondrites.The concentrations in terrestrial minerals from theGamperdown peridotite are similar to those in themeteoritic minerals.

TABLE 11.—^inc (ppm)


Bulk

GamperdownModocSt. Severin. .WinonaHaraiyaMarjalahti. ..Springwater..Johnstown. . .Mt. Egerton.Soroti

n.d.n.d.

n.d.n.d.

192019

35

6171448

5n.d.

6

2019

n.d.

3355

1,86800

1922

TABLE 12.—Gallium (ppm)

Meteorite Metal Troilite Olivine Ortho- Clino- Plagioclase Chromite Phosphate Bulkpyroxene pyroxene

CamperdownModocSt. Severin ..WinonaHaraiyaMarjalahti ..Springwater .Johnstown . .Mt. Egerton.Soroti

2210

65

0.822

0.61

1221

1n.d.

12

172383

6569

n.d.


Germanium: This element was found only in themetal phase of the meteorites. Fouche and Smales(1967) found 128 ppm in Modoc metal, and using thisfigure as a standard we find 280 ppm in St. Severinmetal. Since the metal in St. Severin is about half asabundant as in Modoc, the total germanium contentof each meteorite is approximately the same, about9 ppm. Moss et al. (1967) found 122 ppm and 127 ppmin the nickel-iron of the Barwell and Ohuma mete-orites, which are hypersthene chondrites similar incomposition to Modoc. In the Camperdown mineralsgermanium was not detected in the olivine, and waspresent at about 2 ppm in the orthopyroxene and thediopside.

Arsenic: Like germanium, this element has been de-tected only in the meteoritic nickel-iron; we found25 ppm in Modoc metal, 43 ppm in St. Severin metal.Both meteorites evidently contain about the sameamount of this element, but this is more highly con-centrated in the smaller amount of metal in St. Severin.Fouche and Smales (1967), by neutron activation, de-termined 20.4 ppm in Modoc metal, in good agreementwith our figure.

Selenium: This element is concentrated in the troi-lite, and has not been detected in other phases. Theconcentration has not been measured because of thelack of suitable standards, but using the average of8 ppm for chondritic meteorites determined byDuFresne (1960), the amount in the troilites is about130 ppm.

Bromine: This element was detected in metal,troilite, and phosphate separates, at about the 1 ppmlevel (except for Modoc phosphate, which containedon the order of 5-10 ppm).

Rubidium: As expected from crystallochemical con-siderations, essentially all the rubidium is contained inthe feldspar; the only separates in which this elementwas detected were sodic plagioclase from Modoc(28 ppm), St. Severin (5 ppm), and Winona (12ppm). It was not detected in the calcic plagioclasefrom Haraiya. It is remarkable that the level of Rb inSt. Severin feldspar is only about one-fifth that ofModoc; however, the Rb content of the bulk meteorite(0.8 ppm) is also much below the chondrite average.Smales et al. (1964) have found that the rubidium con-tent of different chondrites is notably erratic.

Strontium: The results reported in Table 13 showthat the plagioclase contains most of the strontium inthese meteorites, although this element is also enrichedin the phosphate separates. Pyroxene contains morestrontium than olivine. This element was not detectedin the metal or troilite separates.

Yttrium: Table 14 shows that yttrium, like thelanthanides, is largely contained in the phosphate min-erals. Diopside from Winona and pigeonite fromHaraiya show a concentration of this element. Other-wise, detectable amounts were found in orthopyroxene,plagioclase, and in the troilite. The amounts in ter-restrial orthopyroxene and diopside are somewhatlower than in the meteoritic minerals.

Zirconium: From crystal chemistry considerations,this element is unlikely to substitute readily for any ofthe major cations. The mineral zircon (ZrSiO4) hasbeen observed in a few mesosiderites and one chondrite,and sporadic grains of this mineral would readily ac-count for the amount of zirconium (of the order of10 ppm) in stony meteorites. The general consistencyof the data for individual minerals in Table 15, how-

TABLE 13.—Strontium {ppm)


GamperdownModocSt. Severin. .WinonaHaraiyaMarjalahti. ..Springwater .Johnstown . .Mt. Egerton .Soroti

n.d.n.d.

n.d.n.d.

10 .40.9

0.50.4

4455

22

280

146

757373

130

86

8762

1110

n.d.

NUMBER 3 11

TABLE \4.—Tttrium (ppm)

Meteorite Metal Troilite Olivine Ortho- Clino- Plagioclase Ckromite Phosphatepyroxene pyroxene

Bulk


n.d.n.d.

11

n.d.n.d.n.d.

n.d.n.d.

0.50.821

1n.d.

9

2315

n.d.n.d.

160 i 2. 07210 2

0.5

Schmitt et al. (1964).

TABLE 15.—Zirconium (ppm)


GamperdownModocSt. Severin. .WinonaHaraiyaMarjalahti...Springwater.Johnstown...Mt. Egerton.Soroti

n.d.n.d.

33

1n.d.n.d.

n.d.n.d.

36

226

2n.d.

60

9029

65018

ever, suggests that sporadic zircon is not responsiblefor the distribution pattern (except probably for thevery high figure in Modoc phosphate, and possibly forthe Winona diopside and St. Severin orthopyroxene).Most of the zirconium appears to be present in thecalcium-rich clinopyroxene, a trend followed also bythe terrestrial minerals in the Camperdown peridotite.The presence of 3 ppm in troilite indicates minor chal-cophile affinity for zirconium, as has been suggestedby Setser and Ehmann (1964); they recorded 6.3 ppmin troilite from the Canyon Diablo iron.

Niobium: The concentration of niobium in ordinarychondrites is not well known, but is probably of theorder of 1 ppm. We have measured 1-2 ppm in mete-oritrc chromite, phosphate, and clinopyroxene, anddetected this element ( < 1 ppm) in troilite, olivine,orthopyroxene, and plagioclase. The Camperdown

minerals contain niobium at approximately the sameconcentration as the corresponding meteoritic minerals.

Molybdenum: This element was observed in metaland troilite separates, with somewhat greater con-centration in the metal; it was not observed in otherphases. Results obtained (in ppm) are: Modoc metal,7; Modoc troilite, 3; St. Severin metal, 10; St. Severintroilite, 3; Soroti troilite, 3. These figures are con-sistent with the data of Kuroda and Sandell (1954),although their results are generally somewhat larger.

Ruthenium, rhodium, palladium: These three geo-chemically coherent elements were prominentlypresent in spectra of the metal phases only. Previoussuggestions that ruthenium and possibly palladiumshow some chalcophile affinity in meteorites were notborne out; neither element was detected in troilite.The amounts of these elements in the metal phases


could not be evaluated because of the lack of suitablestandards. Nichiporuk and Brown (1965) reported thefollowing average amounts in chondrite metal: Ru,6 ppm; Rh, 1 ppm; Pd, 4 ppm. Fouche and Smales(1967) report 6.87 ppm in Modoc metal.

Silver: This element was just visible in spectra ofthe troilites, but absent from those of other phases.

Cadmium: This element was not detected.Indium: This element was not detected.Tin: Tin was detected only in the metal phase;

2 ppm in Modoc metal, 8 ppm in St. Severin metal.This is in agreement with earlier work by Onishi andSandell (1957) and Shima (1964), who found thatthis element is essentially confined to the magnetic(i.e., metallic) fraction of chondritic meteorites.

Antimony: This element was found at about 1 ppmin the metal phase only. Fouche and Smales (1967)record 0.72 ppm in metal from Modoc.

Tellurium: Lines of tellurium are visible in spectraof the metal and troilite, and are absent in spectraof the other phases. The concentration is approxi-mately the same in the metal and in the troilite. Thisis contrary to the results of Goles and Anders (1962)on iron meteorites; they record 5 ppm in CanyonDiablo troilite, 0.09 ppm in the metal; and 1.7 ppmin Toluca troilite, 0.05 ppm in the metal. The equi-librium conditions in iron meteorites, however, maybe considerably different for this element from thosein the chondrites.

Iodine: Since methylene iodide was used in themineral separations (except for the Soroti troilite)the iodine line observed in these separates can beascribed to contamination. Iodine was not detected in

the Soroti troilite. Goles and Anders (1962) recordthat this element is chalcophile in iron meteorites;they found 0.06 ppm in Canyon Diablo troilite, 0.03ppm in the metal, and 1 ppm in Toluca troilite, 0.25ppm in the metal.

Cesium: This element was detected in plagioclasefrom Modoc (0.4 ppm), St. Severin (0.3 ppm), andWinona (0.4 ppm).

Barium: The results (Table 16) show, as might bepredicted, that most of the barium in a stony meteoriteis contained in the feldspar. The phosphate containsa moderate amount, as does the Winona diopside.The other minerals contain about 1-3 ppm barium,except the metal, in which this element was notdetected.

Lanthanides: The data for the lanthanides (hereconsidered to comprise the elements La-Lu) are givenin Table 17 and illustrated in Figure 1. In thechondrites (Modoc and St. Severin) these elementsare highly enriched in the phosphate minerals, andare at concentrations of less than about 0.2 ppm inthe other phases (except europium, which is presentin the feldspar at about 1 ppm). Comparison of thedata for the phosphate minerals with those for achondrite composite (Haskin et al., 1968) shows thatthe phosphates account for almost 100 percent of thelighter lanthanides (La-Sm), and 50 percent or moreof the heavier lanthanides (Gd-Yb). The amountsunaccounted for in the phosphates are probably con-tained in the pyroxenes, which consistently showan enrichment in the heavy relative to the lightlanthanides.

The Haraiya separates, calcic plagioclase and

TABLE 16.—Barium {ppm)


Bulk

CamperdownModocSt. Severin. .WinonaHaraiyaMarjalahti...Springwater .Johnstown...Mt. Egerton.Soroti

n.d.n.d.

<0. 50.8

0.93

0.61

42405172

20.8

1116

13.86

1 Reed et al. (1960).

NUMBER 3 13

TABLE 17.—Lanthanide elements (ppm)

Element

LaCePrNdSmEu. .GdTb . .DyHoErTmYb. . .

ModocPhosphate

51120

1765272.5

304.4

348.6

192.4

18

St. SeverinPhosphate

6413025

100342.5

506.8

4912263.2

25

Feldspar

0.940.840.0930.30

<0. 150.51

<0. 13<0. 03<0. 14<0. 04<0. 10<0. 02<0. 10

Winona

Enstatite

0. 130.330.0800.41

<0. 2<0. 04

0. 340.0400.330.0900.240.040.33

Diopside

3.0112. 1

115. 10.0857.20.836.51.63. 10.322.4

Haraiya

Feldspar

1.42. 10.220.820.300.660.600.060.430.0750.20

<0. 040.22

Pyroxene

0.250.860. 190.950.51

<0. 020.800. 121. 10. 310.850. 131.0

Angrados

Reis

8. 3193. 7

175.51.67.61. 18.72.04 .60.564.2

pigeonite, show the preference of the lighter lantha-nides and europium for the plagioclase and that ofthe heavier lanthanides for the clinopyroxene, aphenomenon already estabilshed for the Juvinaseucrite (Philpotts et al., 1967) and for terrestrialplagioclase/pyroxene pairs. The Winona separates(plagioclase, enstatite, and diopside) show the sametrend but with a larger separation of their lanthanidepatterns. The considerable enrichment of all the lan-thanides in diopside relative to enstatite (and relativeto Haraiya pigeonite) is evidently related to thecrystal structure of diopside, with a lattice positionwhich readily accommodates calcium and ions ofsimilar size, such as the lanthanides. Although thelanthanides are highly concentrated in diopside rela-tive to enstatite, these two minerals account for com-parable amounts of each element in the meteorite asa whole, since the enstatite is much more abundant(40 percent) than the diopside (2.5 percent).

The Angra dos Reis meteorite, which consists al-most entirely of augite, has a lanthanide pattern thatis highly enriched and very little fractionated whencompared with that of chondritic meteorites. Schnetz-ler and Philpotts (1969) report comparable results forsome of these elements. Angra dos Reis show only slightimproverishment in europium, unlike the other pyrox-ene separates. This suggests either that the conditionsof crystallization were such that no Eu2 could form andthat the element behaved as any other triply chargedlanthanide, or that there was no competing phase, such

as plagioclase, that would capture any Eu2 were itpresent.

Hafnium: As might be predicted, hafnium followsthe pattern of zirconium, being detected only in thosesamples relatively rich in this element—St. Severinorthopyroxene and phosphate, Modoc phosphate, andclinopyroxene from Winona, Haraiya, and Camper-down peridotite. The concentration in Modoc phos-phate is 18 ppm, in Winona diopside 4 ppm; in theother samples the concentration was too low for accu-rate measurement.

Tantalum: In view of its low abundance, it is un-likely that this element could be detected in any of themeteorite mineral separates. In addition, the tantalummountings of the spark source are a possible contami-nant.

Tungsten, rhenium: These elements were detectablein the metal phases, but were not observed in any ofthe other separates. Fouche and Smales (1967) report0.52 ppm Re in Modoc metal.

Osmium, indium, platinum, gold: The lines of theseelements are prominent in the spectra of the nickel-iron, but are absent from those of the other separates.Suitable standards for evaluating the amounts were notavailable, but the results are consistent with the figuresgiven for chondrite metal by other investigators: Ir,2.8 ppm (Nichiporuk and Brown, 1965) ; Pt, 8.5 ppm(Nichiporuk and Brown, 1965); Au, 1.2 ppm (Bae-decker and Ehmann, 1965). Fouche and Smales(1967) report 2.11 ppm Au in Modoc metal.


La Ce Pr Tm Yb

FIGURE 1.—Chondrite-normalized lanthanide concentrations in meteorite minerals (brokenlines indicate maximum values) : 1, St. Severin phosphate; 2, Modoc phosphate; 3, Angra dosReis; 4, Winona diopside; 5, Haraiya plagioclase; 6, Winona plagioclase; 7, Haraiya pigeonite;8, Winona enstatite. (Note added in proof: The points for Gd are systematically low, the valuesused being one-half those given for this element in Table 17.)

NUMBER 3 15

Mercury: This element was not detected.Thallium: This element was not detected, except in

those separates for which Glerici solution had beenused as a separating medium, thereby introducingthallium as a contaminant.

Lead: This element was detected in both metal andtroilite separates from Modoc, with the troilite havingthe greater concentration. The metal and troilite sepa-rates from St. Severin also showed lead, but since thesehad been treated with Clerici solution, this elementmay have been thereby introduced. Lead is present inSoroti troilite at a concentration of 4 ppm. Lead wasalso detected in Haraiya and Winona feldspar.

Bismuth: This element was not detected in anyseparates.

Thorium: Only the phosphate separates contain de-tectable amounts of this element, Modoc phosphatehaving 7 ppm, St. Severin phosphate 6 ppm.

Uranium: This element was barely detectable in St.Severin phosphate, and was measured at 4 ppm in theModoc phosphate. The latter figure seems somewhathigh, in view of the known Th: U ratio.

Summary

Although the number of meteorites examined in thisresearch is small, they are representative of the majorclasses of stony meteorites, except the enstatite andcarbonaceous chondrites. The following generalizationsregarding the distribution of minor and trace elementsin specific minerals, therefore, may be tentativelyoffered.

Nickel-iron: The metal phase in an ordinary chon-drite contains over 99 percent of the nickel and cobaltin the meteorite, and probably at least 90 percent of thefollowing elements: Ge, As, Ru, Rh, Pd, Sn, Sb, W,Re, Os, Ir, Pt, Au. Copper and gallium show bothsiderophile and lithophile affinity, and molybdenumand tellurium show both siderophile and chalcophileaffinity.

Troilite: It is noteworthy that the only measuredelement which is entirely chalcophile, appearing introilite but in no other phase, is selenium. Silver, cad-mium, indium, thallium, and lead are probably con-centrated in troilite, although their abundance levelwas too low for measurement. Elements present introilite at the 100-1000 ppm level are Ni, Cr, Mn, andCu; at the 10-100 ppm level Cl, Sc, Ti, and Co; at the1-10 ppm level V, Zn, Ga, Y, Zr, Mo, and Ba.

Olivine: This mineral does not readily accept minor

and trace elements into its structure. Of the elementsstudied only Mn is present in meteoritic olivine in no-table amounts (2000-3000 ppm). Meteoritic olivinecontains more Ni and Co than other meteoritic sili-cates, but the concentration of these elements is aboutan order of magnitude lower than in terrestrial olivinesuch as that in the Camperdown peridotite. Chondriticolivine contains about 100-200 ppm Ti and about 300ppm Cr; it contains about 20 ppm Zn, which mayrepresent about half the zinc in the meteorite.

Pyroxenes: Apart from Ni and Co, which are pref-erentially accepted in olivine, many of the minor andtrace elements with lithophile affinity tend to concen-trate in the pyroxenes. This is particularly true of thetransition elements scandium through manganese. Ingeneral, the concentration in clinopyroxene is greaterthan in orthopyroxene. In chondrites the major partof the lanthanides (and yttrium) are contained in thephosphate phases, but detectable amounts are presentin the pyroxenes.

Plagioclase: As might be predicted, the sodic plagio-clase of chondrites contains most of the Rb, Cs, Sr, andBa in these meteorites. It also contains appreciableamounts of the Sc and Ga.

Chromite: Apart from chromium, this mineral alsoconcentrates vanadium, and to a lesser extent titanium,manganese, and gallium.

Phosphate: The phosphate minerals in chondriticmeteorites account for most of the lanthanides, yttrium,uranium, and thorium in these meteorites. If apatite ispresent, it will contain essential amounts of fluorine andchlorine. Other elements enriched in the phosphateminerals include Sc, Sr, Zr, Ba, and Hf.

Acknowledgments

I am greatly indebted to the Australian National Uni-versity for an appointment as Visiting Research Fellowand for the use of the equipment and facilities of theDepartment of Geophysics and Geochemistry. I wouldalso like to express my thanks to the John Simon Gug-genheim Memorial Foundation for the award of afellowship to work in Australia, and to the SmithsonianResearch Foundation for a grant toward laboratoryexpenses. Mr. J. Nelen provided some microprobeanalyses, and Mr. E. Jarosewich some wet-chemicalanalyses, which are gratefully acknowledged. Dr. R. Fu-dali and Dr. L. Walter reviewed the manuscript, andtheir critical comments contributed greatly to the finalversion. [Brian Mason]


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