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0

Meteor Ablation Spheres From Deep-Sea Sediments

M.B. Blanchard, D.E. Brownlee, T.E. Bunch, P.W. Hodge, and F.T. Kyte

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NASA Technical Memownclun ► 78510

Meteor Ablation Spheres From Deep-Sea Sediments

M.B Blanch, d, Ames Rese,uch Center, Mofl. • tt Vivid, California U.E. Brownlee, Calih ►rnia Institute of Technology, Pasadena, Californie T.E. Bunch, Ames Reseatch Center, Moffett Field, .:a11fontid P.W. Hodge, University of Washint'lton, Seattle, Washirniton F.T. Kyte, San Join State Umveisfty, San ,lose, California

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ABSTRACT

This paper describes analyses of spheres which were magnetically

extracted from mid-Pacific abyssal clays ranging in age from 0 to 500,000

years. The concentration of spheres larger than 200 microns was found to

be a few time3 10 ppb. The spheres were readily divided into three groups

using their dominant m neralogy. These groups are named iron, glassy, and

silicate. Mo:: t of the spheres were formed from particles that completely

melted and subsegvently recrystallized as they separated from the parent

meteoroid bodies. However, some of the silicate spl.eres contain occasional

relict grains of the parent metoroids that did not experience any melting.

► Typically, these relict grains are olivine crystals whose cores are Mg-rich, i !1 ranging from Fo 89-o9 . Commonly the outer rim of these relict grains was

altered during heating. Other relict mineral grains include enstatite,

ferrous spin,-I., chromite, and pentlandite.

The three groups of spheres (iron, glassy, and silicate) may possibly

have some genetic significance. It seems reasonable to expect iron-rich

spheres to be produced during ablation of iron and metal-rich silicate

meteoroids. Metal spheres are probably not produced by ablation of

predominantly silicate meteoroids because studies of fusion crusts and

laboratory ablated silicate materials have never yielded separate metal

spheres, but rather have produced spheres with intergr.own iron oxide and

silicate phases. The iron spheres recovered possess identical mineralogy

1 with the fusion crusts of Boguslav^:a, Norfork, and N'Kandhla iron meteorites

as well as with the ablation debris created in the laborator y using

metallurgical samples of iron and nickel-iron. The combination of several

UIt1l^INAi, PAGE I5 2 r )F POOR QUALITY 7_1 ,` I t i 1

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iron ox i,it' i , Ii as y s ,Intl N I rtt`t; ,. og t i t` n in i tltt l v I dtt l i spIit'rt`t. I s ctlnv i tit , I iig

cvitlt'nt t` tit at'l.lt I ' m t mint tilt- , al l is Ft` - 1'it• I1 Int'tt'Orklids.

s ftI Iit s sv ,{I IIt, I-e a atr y c0Its dvr . at.l y unar y Fv - rich t h.ln t ilt` t it'.It v

^+.{thl`rl^r: l'hr y c ollsI-it tit nl. ► l;nt't iIV . Intl a Fe ,; i. ► S: : wIli,`fI IS r al.1t ivvIv law

ill tii. I'hia coulhi it. II Ikill Is n I.( I Ikcl y prodile `t1 b y .II`i.it it'll t`1 nit`t.II - rtcll

c,ttl` motcttt'a1tl:+.

TIle asi l icatc ,I`II%. I F % .11't' unti. , itI, tt'til y der ivt't1 fPant .lhIitt ian of stilly

mot voraitl-l. 1'llo al Ivillt`-magilct itt'-t',l.iria Aild cult ide milict.tl .1Ss4'1111,1v%-,v; f

avk, u ' I, illy; I it t lio!w sphcrt`:i .irt` IdVIIt I t'.1 I t 0 t Ill t tit` tit'Kt' l' l ti ed 1 11 t lit' 11.1t itr.11

I Its Ia11 t ' rll:tti al AIIc1ltlt'. l l rgut ' II. ,111.1 %Iu%'11 'it'll 1110tV, , I 1tv s .IIti.1t It`It dobrIN

treat ctl Ili t lit' I.11t tl r . attlrv. . tll,l Inc I t t' tI illt v {` I.illot .11" y &Ill1S( t'.' I Ion t t'tl f 1'01M

i tIlc Strato 1111t`rt', lilt l k t', t m{t aaitI t ll ti all.i reI ict I`r.11n:i .11'0 list , tit tat"

'let "I in.I it i iv, t lit` part'llt 1110t ti ara Itl t y {lt`H 1 ar tilt` tii i it'.tt t' Sl, ht`rt';t. Illl I k

.II1.1I v-,vs o I, vt r v s t .1 i I 1 . • t`tl s1, itv I- v-I II.IVi' tihaWII t 11.1t I1t`I1VO1.1t i I t' 10111011t .11 r^ t ' IhltlUi.11lt'cti . Irt` SIinII a r to t 'halidr Itc . tl`mid.itice s Alm IN- tit';: at FVI IC ,I.itIIlti I

^iolllltl tIt .1 1t'W I)0rt'" 11t a! t llt' a{'llt'I't 'ti) have itit'Iltlllt ' tl I1111'.lt` rOils 11 t1;11

tt`mporattlrt` Inill01'.11: 1 wh ich Oi tt'll t't • . " 111" .Iti 1.11. 11 I- ct' y tit.1h; ill .1 tlilt'-t;Yaillt`tl i s m.ltt"ix that is ch.Ir :lctt'rI.• cti t'v llll III cl'anti : it'cu1.11 raitlti. 1'hctit' vat.la

Were c:llltictl by t'tit• .11t i11 ►; y atat ilt`: It'. !; WAtt`r. Slllitlr) pratltit'atl '. ' y do,'0111-

i10:iit it'll Oi IlV,Il'.It t`t1 . Illtl .'t ht'r law t t'1111't 1 .ti tlrt' millo r .11:1 dill illy; .It`1.1t it`ll.

lirt'.lutic t.lrl;t`r citstalt. of httJwl .ltitiaci:ltrtt 1,lth

f ill y -gi.iiiiod. low t t'i71por.It tire. y al.lt i la-rich m.lt 1't\. t he ah y iallri Calldi.l.lt t`s

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1. Introduction

Over a centu:y ago, Murray and Renard (l] discovered microscopic

magnetic spheres in deep-sea sediments. Finding both "stony" and "iron"

types, they suggested that the spheres were produced by the melting of

meteoroids as they entered the atmosphere. Since their discovery, deep-

sea spheres have been subjected to a variety of investigations, but their

importance to the science of meteoritics has not been fully recognized.

Reviews of much of the early work on the spheres were Liven b y Schmidt

[2] and Parkin and Till ,­ 13]. Most of Lite previous work has concentrated

on the "iron" spheres which are reasonably well characterized and under-

stood; their credibility as extraterrestrial particles is now well.

established. Evidence is strong that the "iron" spheres were produced

'ay atmospheric melting of iron meteoroids [4,5). The "stony" spheres

i have only been studied by a few investigators [6,7,8], and they are only E

now being extensively examined with modern analytical techniques [9,10].

The "stony" particles have not generated much interest because their

properties were not understood, and there was no real evidence that Che

particles were, indeed, extraterrestrial. The "stony" spheres have been

interpreted as droplets produced by ablation of stony meteoroids 16,71 and

mistakenl y identified as "rounded bodies in space" not altered by

atmospheric entry [8]. In this paper we direct most of our efforts to

the "stony" spheres because 0 ey are the least understood and potentially

the most interesting. It is the purpose of this paper to show that the

"stony" spheres are extraterrestrial and are generated by ablation of

parent meteoroids similar to chondritic meteorites.

^11tIGIN AL "0'' 15 '' I OFp(I^R l?l1Al,ICY 4

f

The m. ► I or t echnitlut' we hav • used for ident if teat ion anti in c rI,ret at Wit

of ah l . ► t it'll splivres is a detailed cttnlpar i son with natural .utd l ihtlratory

ablated materials. i'revious work has established a sr`t tit cr i teria for

idt'ntifying debris prodticod b y atmospheric ablal tote of meteoroid btldics.

These criteri. ► were derived from .in- ON, st`, tlt nu'1eorite fusion crusts ( I1-111.

ablat h i ll debris tit tilt' stratosphere , 141. and matcrial prtldllt'ed b y laboratory

ablation of oli\'int • 1111, nit't.11Iic Ft' .ind Ni-Fe 1121. Fe-oxides 1151. anti

a t• .1rbtm It' etll ► s ch l IItiritr (:ttlrt'lll son ) (1 I .• I- iteria usettll for identifyin;;

ablated eAt l".il el'1'l`Nt ri.il m:ltl'ri:il .11"t' .1N 1,11 IOWS:

(1) Ovetirrence elf diseyui I flit-him mint'ral phases (e.g. , w7 .t ite, glass

All '(111t'd o iviIIt') dIIt , tt , lilt- it ing .1114 r.lpld "ooI ilip.

(at.) i)1-it.I tic t ive textures (v. g., . - oiled o1 ivino .,tirl"01111.it'd h\' m.it'11t't IIt•

crystals in a ):rt'untinl.iss of produced b y int rrgrown dissitni l.lr phasys.

l 0 Ileplet it'll Anti migration of volat i It , t`lt•motit s (e.g. S. 1'. C. CI j Na. 11,0) t111t' to licat int:.

(!) Frat'tioiiation and conevIlt t'.It 111 11 tit less Vol.lt i le clt'Itlt'Ilt4 ill

SOMV 1101101 - al hil.lse`: .ICcording to I heir :it i illit y for oxygen (e.g.. Ni-rich I

metal coves surrounded by Ni-pour oxides).

For iroii netcoroid p.lront htidics. the' mot.il is tlxidiZetl. and wllst itc.

m.i);llt't It t`. Ill,! ilt`111,11 it are torllt'ti. sinct` iiit'kei is not ati easil y oxide.-cd

!ls iI- 011, II t'OIlt't'1111.I10s iit a lilt , I.II i is cort'. Fit I. t- holltirit it' ill.ltt•rials

(t' • !t.. A 1 1 oilkl y . tillrch i skin . and Orgiie i l ) , two melt i'll.tses are t orined . Hit,

d1 1 111i11.1111 1 1 iLINe i:; .1 sitiCitt` nit , it %diicIt crystaiii.- vs t form gr.lins, lit 1 i. 701141 d t'tllledraI oIivitit , ,inn imignt`t itt , ill a Ca, Fe.AI, 1, l- ?.Ia ss. matI- ix. The

5 ref - 1 T- T l 1 I ! ^..: l i j . r i7

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other phase, containing Fe, Ni, and S, crystallizes to form iron sulfides

(pyrrhotite and/or pentlandite) and iron oxides (magnetite and/or wustite).

Both phases produce spheres when sprayed off an ablating meteoroid, and

it is common for silicate spheres to contain inclusions of sulfide minerals.

2. Experimental Procedure

Because studies of fusion crusts and samples ablated in the laboratory

produce magnetite from iron-•bearing materials, we expect most meteor I ablation debris to be ferromagnetic. For a meteoroid to ablate without

producing magnetite, it must have a very low iron content. Therefore, the

spheres in this study were serarated by magnetic extraction from 3 kg of

globigerina ooze and 100 kg of Pacific red clay. The samples came from j

box cores taken from the top 50 cm of mid-Pacific abyssal clays in water

depths of 5,000 m. Assuming an average sedimentation rate of 100 cm per

106 years 1161, the spheres in these sediments range in age from 0 to

i 500,000 years. The separation process used a magnetic extractor suspended

in an agitated slurry of sediment and water. The magnetic fraction was 1 i sieved to remove particles larger than 100 hm and ultrasonically agitated

to break down fecal pellets. Spheres were hand picked from the larger

size fraction. This process was efficient for separating weakly magnetic

(i.e., silicates) spheres larger than 100 PM.

Over 700 spheres in the size range 0.1 to I mm were selected, mounted, 1 and analyzed with the scanning electron microscope (SDI) to study surface 1

morphology and elemental composition. One hundred and fifty spheres were

sectioned and polished for quantitative electron microprobe analysis and

A(^ F Vr X1 6 OF POOR l t^ 'H 71 i

S124 studies of internal textures and individual crystals. Over thirty spheres were subjected to -ray diffraction, usin ►; a Debve-Scherrer powder camera, for major mineral identification.

3. Results

The concentration of spheres larger than 200 frill was found a few time:; to be 10 ppb in the red clay and about 1 pph in the globigerina ooze.

It appears, however, tha t ,ether clay samples and different extraction techniques (work in progress) may produce yields of spheres of as much as

400 ppb of dry sediment weight for this same size range. The spheres were readily divided into three groups using; their dominant mineralogy.

R.ised 011 their dirt ilh'tiVe mineral and chenlic.il compositions, these groups are name irotl, jjAsliv, and silicate. On the surface, the iron

spheres were black and shiny, the silicate spheres were rough and ,lull,

and the glassy spheres could not be distinguished opt ic,ill y from either

the iron or silicate spheres. Any smooth surface the silicate and glassy

spheres may have once possessed had been etched away by seawater action

(Figs. 1. 2, and 3). Sphere shapes ranged from true spheres to spheroidal

and b0tton-shaped objects with protuberances (Fig. 4); some irregular

fragments, presumably from partially decomposed spheres, were also

recovered. (All particles are collectively referred to in this paper as

:spheres.) Several spheres contain relict grains from the parent meteoroid

body. Since some relict grains have not been altered, they provide a

basis for deducing the nature of the meteoroid holies from which the

deep-sea spheres were derived.

7 1

r ,` 1

1

I

3.1 Iron spheres

The general abundance of the Iron spheres ranged from 25 to 50%

of the number recovered, depending upon the core sampled and the magnetic

extraction, procedures employed. The elemental content of these spheres

is mostly iron with varying amounts of nickel and occasionally small

amounts of other elements (e.g., Al, Si). The mineralogy of these spheres i

11 includes various iron oxides with or without metal. Spheres always

contain magnetite (Fe 30 4 ), usually contain magnetite and wtistite,(Fe(i),

and occasionally contain magnetite and hematite (Fe 20 3 , may be either,

primary or secondary). When present, the metal phase associated with

these iron oxides is taenite (YNi-Fe). The magnetite and wiistite commonly

form oriented, multi-crystalline, interlocking aggregates as in Fig. 5.

Cell dimensions of the magnetite crystals are usually small, indicating t it is often a ferrous trevorite. Wtlstite cell dimensions are variable

t but :n one case it is nearly stoichiometric FeO.

Several iron spheres contain eccentric Ni-rich cores which are

usually metal (taenite) but may be partially or completely oxidized.

The sphere in Fig. 6 contains three phases: an outer shell of magnetite

^i (Ni-rich, containing about 25% trevorite molecule); an inner metallic core

(crescent shaped) of Ni-Fe, containing 89% Ni; and an inner oxidized

core (circular) containing 5U7 NiO and 7.5% SiO ') . This oxidized core t' has been identified as a siliceous, nickleiferous trevorite with a

I1 i composition of Ni(Ni .28 Si. 15Fe.57)204. The oxidized portions of other

cores commonly contained some Si. In some spheres there is no Ni-rich

1 r

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8 LT j 1

()ltl(;INA1, OR PAGN, IS Pl.Kll{ (111A 1.1'f Y

-ore, the significance of which will be discusred later. Iron spheres

of this type have been previously described 11,3,8,17-231.

3.2 Glassy spheres

Less than 10% of the deep-sea spheres is characterized by a dendritic

network of oriented skeletal magnetite crystals with an interstitial

glass composed principally of Fe, a minor amount of Si, together with

smaller amouts of Mg, Al, and Ca. one of these spheres, shown in Fig. 7, I^

possesses an eccentric Ni-Fe core containing; 38% Ni. These spheres show

a strong resemblance to spheres recovered from manganese nodules by 0 Finkelman [17,73). I

3.3 Silicate spheres

The silicate spheres are the most dominant group; when viewed with

the SEM, their surfaces show euhedral olivine and magnetite standing

out in bold relief (Fig. 8). olivine and magnetite crystals are often

aligned in a brickwork fashion over large portions of the sphere surfaces.

The interior of the silicate spheres is composed mainly of olivine

and magnetite crystals surrounded by interstitial glass or voids. Grain

size is variable for the olivine and magnetite. livine crystals

range from about 1 ltm to 40 lim in diameter while magnetite crystals J

range from submicron to only a few microns in diameter. The two most 1 common textures for there spheres are larger equant (unoriented) olivine

crystals with smaller magnetite crystals surrounded by interstitial

glass, or voids, n ►- parallel bars of euhedral olivine crystals with magnetite

9 11

Tz- Y' ^. ^ ^ ' ^ i 1 1 _ 1 1

and glass occupying the interstitial region (Fig. 10). This latter type

resembles "barred" chondrules in chondritic meteorites except for the

presence of magnetite. The composition of the olivine in the spheres

ranges from Fo S5 -Fo 80 . This olivine is always zoned and Fe-rich along

the boundaries. The magnetite may be pure Fe 304 or contain several percent

Ti, Cr, or Al, substituting for the Fe. Conposition of the glass varies

among the spheres. The glass is an Fe-rich silica with minor amounts

of Al and Ca and 'rtually no Mg. Usually most of the Ca in the spheres

occur in the glass, whereas the Al occurs in both gloss and magnetite.

This glass contrasts with that in the glassy spheres (described earlier)

because it is enriched in Si, Ca, and Al and contains considerably less Fe.

Other mineral phases usually occurring in the silicate spheres a.e

pentlandite, Ni-rich troilite, and chromite (relict?). Figure 11

illustrates a sulfide-bearing silicate sphere. i Occasionally spheres are encountered having a matrix of very fine-

grained material, including olivine, magnetite, pentlandite, and glass with

numerous vesici,^s that were apparently produced by volatile gases leaving l

the matrix. one of these spheres is illustrated in Fig. 12.

Nearly all of the silicate spheres have experienced etching by

seawater. For some spheres, not only has the surface been severely etched,

but the interstitial glass has also been completely dissolved away. In

extreme cases, as illustrated in Fig. 9, even the Mg-rich cores of

1 k olivine crystals have been dissolved leaving only an Fe-rich olivine crystal

boundary held together by a skeletal framework of magnetite.

0it1GlN P-L Y ' 'is l)tJpl.l'f• OFD P00 11

10 a

F.lement.aI compositions for the silicate spheres show an iffinLty

toward chondritic meteorites. Although the surface compositions of these

wpheres often strongly deviate from chondritic abundan c es. the interior

portions of the spheres agree more favorably. Nineteen spheres possessing

glass, .► low void space, minimal alteration by seawater. and containing

no relict grains were selected for bulk .inalyses with the electron micro-

probe. The results of broad beam analyses of polished sections are

shown in Table 1.

Most of ' he silicate spheres were formed from grain y, that comlIletely

mt- l t ed a; suoseyuent l y re: rvsta l l i zed as t hev separated from t he parent

reteoroid body. However less than 10t of these spheres contain occasional

relict grains of the parent meteoroid that did not experience any melting.

l'vpically, these relict grains are olivine crystals whose :ores .ire Mg-rich, rI

ranging from Fogg to Fo 99 . Commonl y . the outer rim of these relict olivine

grains was .altered during heating. 'Those altered rims have Compositions

rs low as Fo S11 . anther relict mineral grains include enst.atite. ferrous

i spinel, chromite, an.i pent land ite. ou.ant it ative microprobe ana1vses of i sumo of the relict olivine grains are given in fable 2. One of these

sh' res. shown in Fig. 13, cont.sins .a large (''1110 lim) olivine grain (Fo991 i a^ whirls has a Ni-Ft- inclusion with 7.3'.; Ni. surroun,ling this relict grain

are the typical reervstallized phases of olivine and magnetite. Another

sphere, shown in Fig. 14, contains an assemhlage of relict grains which

include olivine (Fo 97 ), enstatite (En 99 ), a vein of Al-rich material

1 ^• I.

(307.. Al 2 0 3 , 15% FeO, and 52% M "O), and numerous micron-sized grains of

pentlandite (relict?) in a fine-giained vesicular matrix.

The outer rim of this sphere consists of recrystallized olivine

and magnetite grains (thc glass has been dissolved away).

4. Discussion

4.1 Comparison with chondritic abundances

The compositions of the relict olivine grains and the recrystallized

silicate spheres are similar to chondritic meteorites. The results of

electron microprobe analyses of relatively unaltered silicate spheres

are shown in Table 3, which lists the principle elements in atomic percent

ratioed to Si. This table compares the composition of these silicate

srb e y es with that of C1, C2, H, and L chondrite meteorites. All of the

elements are within the chondritic range, except Ni which shows a strong

depletion (up to 100). The trace element analyses by neutron activation,

performed by Ganapathy [241, of single silicate spheres from this collection

have also shown a chondritic pattern for the following nonvolatile

siderophile elements: Ir, Os, Sb, Ku, Sr, Ni, Co, Cr, and Sc.

'i There arc several possible causes for the differences in elemental

content between the spheres and the chondritic norm. These include the

following:

(a) Inherent elemental and mineralogical differences among the parent

meteoroids producing the spheres (e.g., comets versus asteroids). ^1

(b) Fractionation and volatilization caused by different melting '. I

temperatures of various minerals during the ablation process. Volatile

12

--.-r°—'_ - -^.^....'_. - --,rte, ^--- __ ;,, - --_ --_^•,►.••^'- J' PIT`' s I I^

i ►KICINAL PA(; E, IS OF !'WR QUALITY

elements, such as S, are vaporized when iron sulfide minerals (i.e.,

pentlandite, troilite) melt. There is a marked absence of iron sulfide

minerals in most of the recrystallized silicate spheres. Laboratory

ablation of a carbonaceous chondrite (Murchison) produced small quantities

of a sulfide phase as well as the ubiquitous recrystallized silicate

phase 1131. Studies of the fusion crust and ablation debris revealed

that nearl y all of the NI :end Some of the Fe of this meteorite was

entering; the sulfide phase and producing Fe,Ni,S-rich spheres. Similar

spheres, usuall y 10 pm in size, have also been collected from the

1 stratosphere 1141. It .appears that during ablation Fe, Ni, and S combine f l

to form small spheres; this may possibly account for some of the Ni r t deficiency in the deep-sea silicate spheres.

Fractionation produced by differences in density may possibly separate

metal droplets from silicate droplets. While much of the metal Fe is r being oxidized, other siderophile elements (especially Ni) could become

concentrated in the coic sad subsequently be thrown out of the silicate melt

(,due to rapid rotational forces) or fall through the silicate molt as the

sphere decelerates in the atmosphere. Even for silicate minerals containing;

small :amounts of Ni, the Ni could migrate into the coexisting metal phase

and ultimately become separated. Because silicate minerals in chondrites

are usually Ni-free, the spheres would be depleted in Ni. The Ni depletions

shown in Table I and Fig. 15 perhaps are best explainvd in the above manner.

(c) Grain size of the parent meteoroid could also produce mineralogical I

fractionation in spheres. Parent bodies having very small grain size

(relative to sphere diameter) and few volatile constituents would have a

11

TL - r- 7^Iw^1 . .-. ^ 7 i^

ti l IIt1 • Ilt'y to 111*ad llce %-IIt -in ica1IV ho1110g t`Il,nlh 1411 11t`res. Part',It bodies having

very large grain :,liar (relative to sphere diamctor) and tt , t, volatilt`

"011st i t it' IIt :I won 1,1 t ell,I to pI-„,Itwe a var Iety of -.it , h, , res w it It d If I' ert-tit

mineralogy. both mo tal l it • ,Intl ::i 1 it'At' x1111101-VS Could ht' 111-0dureu by 1

Iragim , ittA ion and abl.It ililt from only one coat'rtr-grained mt't.II -rich :;i 1 icaty

parent meteoroid.

(d) t'hemic.II dissolution and t`tchin l; art` ►'t`r:porlSit'll' for rt'movinl:

the gtasa phase .Ind the Mg-rich :ore of olivint` crv::tak in the rv- I ,'rV .-;t a l l i .'t'd spliores. Untlttllht t'd I V . tilt` .It'.Iw.lt 1`t' . ► f't toll will challge lilt'

rel.lt ive amot111t H t'1 Mg, Si t Al, .md ('.1. tiillt-t' tilt' Al and (al are t'ollcl ` Iltl'.lt t'd

in the g I.I:; : : (t ht' 1 ha.,.f' most re.Id i l v ai foct rd b y t't ,'h i t1Y.1 . htl l I: .In.l 1 vrlt`;1

showing dr11 I ct i onti of t ht'St, two r i t`Illent s probably tit, 11t't re I i t`,' t t ht` t ori,tin.11 sI, It' 1'0 t'onll'osiI ton g . Tit I:. 1`t tcct i:. t I lur:t rat t • d in Fi !',. I1, Where

( ' ,1 ' Ind At ('alit t'llt ti t i t ... I {t',It c ::Ithtl l-v : .Ir y t'01111 1 art'tl Willi ,'houtil' l t 1,' 111t'I l'oT-III` 'r value~. All but t ive of the sphcros 1.111 tin tIto 1'. ► /Al l Int` and have a tlun- ' 1 d,lllces coil~ i :;t cut w i t h chomlr i ( 4 , ... I ht`:,t` cs ::Iltiw ,It'l l 1 ct if'll:: 1 1\'t` Split`1- P1

M Al .Intl/o1 (%1 tl', i lll Ch"11,11 it it' vault`:: prob.lbl y twi-all:w t i t tic.l \:.Il cl' t'tchil1):.

.1.-” Ori li ► t .tj' flit • i Tk1 ► : , .

The ! hrt't` 1;rrult,; of ::1iht • l-cs ( I rtin, ll I.1::s\' , and s i I i c.It r) In. IV lift::. i 1` 1 v

II.Ir. Sonic !,t'nt't it' :; il;ll i 1 it-.11lt't', i t >:t`vals t'c.laillablt` t t1 t`xltt t' S i l'on-1' I,'h

Fph-ros to I l l' 1 1 1, 0dll,'t`,1 dill'{111; ,11 , 1.1( it'll t i t {mill- .Illd IlIct.11-1- tch ::ilic.ltc nictt`oroids. Mot a1 spht • I't• a .Ire 11 roballIV not liroduct`.i t'v .Ihlal it'll of predomi- 1

11,111t I ::I llcItc Iltt'tcttl't' Ili ti Itt`,',111.:' -,t till ll'ti of I its ikill t'rtL•:(:: ,IIld i.Il t t t I It,'r all 1.11od :;ilicatr nl.ltt-rial'; 11.1ve nt'vt`I' \it'i,It'll :;Opal'att' nit'tal ::1'htr4 • hilt

14 have pto•.e:ced spheres with intergrown iron oxide and silicate phases.

Even though there is a relatively low abundance of iron.- and metal-rich

silicate meteorires, it is not too surprising that such it large quantity

(25 to 50%) of iron spheres was found, laboratory ablation experiments have shown that metal samples produce an overwhelming amount of spheres

(>00%) whereas silicate samples produce a much Smaller quantity (-257).

The iron spheres recovered possess ider► •.ical mineralogy with the fusion c r usts of iron meteorites (i.P., Boguslavka, Norfork, and N'Kandhla)

ill as well as with the ablation debris created laboratory using metallurgical samples of iron and nickel-iron 112]. The combination, of several iron oxide phases and Nt segregation ill individual spheres is convincing evidence of ablation from metallic Fe-rich meteoroids. The most common mineralogy is an assoication of the various Fe-rich minerals

(i.e., taenite (Ni-Fe), wustite (FeO), magnetite (Fe 30 4 ), and hematite

(Fe 2 0 3 )) several of which are often in a single sphere. In the absence of industrial contaminants, the presence of the metastable mineral vrUstite is accepted as sufficient proof of an .:L)lation product j12, 251. Another equally important recognition feature is the formation of a metallic core enriched by Ni.

4.3 Orrin of the glass;e spheres

The glassy spheres are considerably more Fe-rich than the silicate spli-res. Glass ill these spheres is relatively low in Si, and the spheres f A do not contain anv :silicate minerals. This combination is most likely produced by ablation of metal-rich silicate meteoroids.

15

.- OVA

^. ,')•: .riot If the Ni ; 1, 1.111/ elf l ht l t•t It

I' llt` tit Iic•it 4' 4ilt it , 1t'.I .Ire %litd k i t It , t vd IV deri ve11 11, 1 111 .11/l .It 1 , 1 11 of .: t ,111\'

111Cte 0 101ids. T he ,llivilll ' - 111.11;1111Itv - g I.1:: :: .111,{ :;uII I ' ll , IldIter.11 . INli4 '111111.1);1.:

tl ecurI' 111 1; in t 111 :1 l herra .trr itie11t l,'.l l t t l t IlOSO , t-Wt' it1 1,i 111 1 he 11.11 ill it I • ,

I%Isitlu %, rt1-4t: • AI I, 11,11, t1r l;uei I. .III.I M I .:ln I I, I I.. , (II. .,1 , 1.If i,1II

,it-bii ti cIc-It 1,1 ill flit' labo1.1tt1 t• \• I1', 1111 .1 ,'.Ir14 1 11;I1etltlti \'il,`lldri(1 I I i I. .Ill,l

111111 k ,'•';. 1.111,'I .11 . v ,{II::t i s . 11't i,' I% , S ,, 1 1 I,','t C,I 1 1 4)111 I lls' .it r. t 4, 1:: I 1 h 4` r t'

I I .1 ^ III t lic ::.'Vt•V.II W.IV- ; (, l di'd uct` (1111 1 1"Ill.11 ioll .k boll t 1lttss1111v 11.11111(

I till' 1 t', 1 r1 1 {1{:. ItI Od111'i11); .: i Ii,'.I t t' ::111 It , rt`.:. Wt • w I I 1{i.;i Its , woiIt1, 1 1 1 1 1 11 v4.1 1,t

gva Ills .111,1 hilli. spilort, Ch11111:;t IN Amt Ivr:1 11I re ict );1'.1111:: havo

04 , 111 it lied the I o I I owiur; Ili i lit- l,11::: Mg-rich 111 iviIIv. vIIs(.It it1, Iorruus

spIlicI. lit , ntI.Ilnii(v, (I- oiIitr. AI - rilh :Ili tic l(:'). cItr,anitl. And Ni-F1

Inc I.II. M11::t , 1 1 the.it' 1111111.11: 0,•0111 .r.: l.It^,4 r crvrct.11 . . in .I I tilt.-

.1'.1in1,1 Ill. Itri\ III.It i:; 111.11'.11teri:Olt 11\ 1111111t`rtlu:; iv . It I v11i'Is The:;1

VO % I1 , Wk , rt' 1.111.;141 1 1 v t' .;c.111i11 ); v,11.1I i It':. I,1 1, . \:.Il eI . .•111 1111 ) 11l'.hiil,'4',l

t 1 \ .11.'1 1 11111 , 1 :: i I h i ll ,11 IIv%l r.lt 1',1 .111,1 , 1 t lit`v I Ow t 11111 1 1'1'.11 urt' 11111:11 .1 I:: ,lilt' 1111;

11 1 (.1( it 1 1I. 1i1,•.IIL:1 I.I11;t`t' i I* V .; t . I s , 1 1 111%;11 t1'Illl`11'.Illlll' Ill ilicl'.1I .1 re

.11 1,1 w'it It :1 t 1111 ) • 1.Ii111,1. Iow (1111 1 11.111111. v, 1 1.1t 1 1e-ril I ill. ItriX.

l 111 , 1 1 1 \' i,11'•; ,.111111,1.it t`;: 11 1 1' ; 1 .11 ('ItI 1114'( 11 1 1'1 1 1%i: . .It 1 ,',Ir1h 1 11.11t`4 1 11.: 11l0ll.ir i t t'.:.

till Ik .111.11\'.:1:: , 1 t ::j1IIcI.,!; :; I IOW ilig I II I IC ,1r 11, 1 .;i 1t •'114 . 1111 .'l

wo.lt lit , ri11,: 1 1 \' .:4'.IwA14 , t' and not 11 1 11taiit1;1); 1'1111t 1;r.1iIIs I'll. 1v .I I:; 1 1 ' tlaetllI

t, 1 1 ,l1,I11,' illl; 141::.:ibIv 1 1 .1I"i'll1 1114't 001"01kl::. t111t' .:11111 .1 ( 4 , 1111 1 1 i:. .;I10 it ill

1'.11 1 11 •, . Ill tIIi.; till thod t I11 .I::::nn11 1 t i11n i.; 11.1,11 1, 1 1' :;1 1 111rt'.: Wit i"It .1 re

MIA l I CI (',I t•':1.1\:.1111 Ct ch111); w"LlI,I ,'11.111,'..' 1111 C.I/AI I .il 1, 1 hot%IUti1 ::, 1 1:It' .11

t 111 A l i s i it t 111 nl.l ) •.111 t I t 1 .1:: w• e I l as ( 111 i ' . I - ht`;t 1 i u ); x',1 ass silk{ L010%. 1111

t. tii);I1 , 1 1 1;.1:: \'CN1,'Ic!;. IIi.lt ii th1 1'.IIAI 1.II 11 1 .: t.11 I \:itIIiit the ,'1i, ndI Ill

I I1 Fl y-

A^ i ?

range of i.0 to 1.25 (27,28], then other elt,ments have not butt depleted and will correlate with the hulk chemistry of the parent chondricte meteorite type. In Table 4, spheres 1125 and 33 I ► .lve the proper Ca/A1 ratio. Hie Fe, Mg. Ca, Al, and Si contents for these spheres match the meall composition of the type 11 anti enstatite ehondrite meteorite g roups.

A more rigorous study will be necessary before it can be determined if this method is it meaningful wary to correlate hulk sphere chemistry with possible parent meteoroid types.

5. Conclusions

The mineralogy and chemistry of the deep-sea spheres are identical in many respects to the meteorite fu,ion crusts, laboratory created ablation debris, and the ablated interplanetary dint particles in the stratospheric collection. The principal differences are the unusual textures (e.g,, harred olivine "chondrult,s") rid the relict crystals. All of the spheres anal y zed in this report appear to have heen produced during ablation oI larger meteoroids by mel: ing, fragmentation, and vaporization.

Althou!•,h these spheres are not ahund.lnt in beep-sea sad iment s. thev were abundant (1 to 10" by weight) in the magnetic fraction larger than

200 lim in size in uur sample~. Because the natural sedimentation rate -4 for .abyssal clays is .about 10 tam per year, tilt, spheres are more concentrated .n the clays than in any other terrestrial environment.

There are very few magnetic terrestrial particles in the sediments in the same size r.ulge as the spheres, and extraction and identification is a relatively simple proces,.

17

^ Mew .r• - L I I

1

1

1'114' h i t;h atmildallk . t' l "1 to SO%) 111 tilt, i roll S1 1 114'ra':i w.l:. :.Ill pt t s i tig.

.Ilf htlligh Zia• if 11.1VV .l I'OSSiI , Iv t'xpIallat It ilt b.Itit'tl till I.II, oI.itt t l t' .11,111 toll

t'X1tt'r IIllt'llt :+. Ihlwevt'r. i I t ht' llt'at 1 \• 0,111.11 .ltt.lut I t it • :: .11 t t-on .11rtl :i i 1 i.-.It t'

s plit 'rt'al th1 t'VI I VC t Pre-allI at ittn .II'mul.1Ilk' . t ht'ra' 111.1\• 11.Ivt' 11. 1 . 11 .t lilt' 1.11-

rI:11 k , 01111 1 0114 .`1 lilt' :.11t'1'4 t :: 14t11.; 111t'It't1rt 1 1i!i lltIriIw. tilt' I.Itit 11111,11111)

F . V0.11 t It the th' : lll'1'l'1t:N t' 1 rt'1 i:t F,...11Its . 111.1 1 111' 1111111 ti1 1 ht'I't' :0111I1 1 1 :iI-

t tons till};+'t tit I1 .11't'llt slit, t1'.' 1 altla t t t :hlllltlr l t I.' t'011111 1 :iIt It'11 t.'1 t lit' i I t.'aty

:;l t llt'It':i. 1'llts f :tlllsIs14'11t alllt Ilit- .111.11 y '.1'14 1 1 1 11111.11' it1i 1N 111.11

i lid It . at y that tht' Ill,tall is itC CIt't luy, :hotidt it i s tit, itvvI .II I'ht' Ni

tit', 1 t'll.' y Ill t hr :I i I i:.11 1' spilt' 1 +':: i tI rt'.1:i ► nai l I y wt' 1 1 IIIl.lt'I ::t 1 1 1111 .111.1

1 1 1'1 1 1 1 .11 + i \• 1114':, 11. 1 1 1't`I I t`.' I .l N i ttt't i t' I1'11.'\' lit t Ii-t , } t .irvilt Illy 11',`1'11 i it:..

, M. tvor .itll.11 1. 1 11 :i1 1it'i t' . 11'.'1 1 \'1'I t'.l I I0II1 .lot , } 1 :.:.1 !wtt11114 , 111 Ira' \'.II^^.^^`1+' 1

t'Xt I -it 01'rl':it I {.l 1 111.11 t'I {.l1 1`t't'.Ill:a' t ht' y PI.Iv \ {Il at1►Ilt' t'.V. VS 1 I . I , r 1':.1.11!

: 1 :i.11ill' 14'•. .1I 1111'1 1','1"111.1 1 1',':. 111.11 .II t' t . 1 , 1 I I t 1 t m . v { \'t' at lit' t ti1 11t'1 1.'

11.1:.'..t1',t' .11111 1't':1lllll' tilt'l 1'. 1 t i tvs A t111ltlilt- \• .I I tit- 1 1 1 I lls' ::}1ht'11'.'i I (h.lf 1

tIl1'\' 11 1 1 1 \'Ide .I 111 1 !..•1 I' 1t' 1:.1\' t. 1 t11.1\' tIli' ,11'11'.`.1t {1 4 11 t 1 l 1111' t'.Itt h 1

11`11 ; as 11 1 yt'.11::. 1, ..:111 ; tllt'tt't'I.`I.l: c .1:: .1 l lltl,'I ion 1 1 1 t {tilt'. pvI II, tit:: .1 : X 1

^.' {^ i 1.' 1: 1 a',{ }, 1'111' 11 t

:^t 1 11k' , 1 1 I lit' ;1. w1'1'k .Ill.t Ill l.' I 01 1 11 - 1 1 14' 11.11 .1 1 1 I 1".t'11t t'.t ill t Ili:: }'.1}11`14

W, 1:; 1tt'1t01'111:1t Ill Ills' I ' IIt'.`I't'tlt'.11 .1111{ 1 1 I.Ilw I \ ; fIIdit, ;i ltrall:lt I oho r.Itoriv.;

.it \llic . ; 1%t':.t'.1r1'11 1 ' t I I t t'I t`\' I1. 1 lilt '1 I . 4 14 1 .111,1 . 1 ,`,' 1 1 I'. I lilt. III, 11'1: -F11v i I , t tlnit'Ut .I 1

,^ILll y :iiri I.abor.lt .`t lc .. RL' . 11111, 1 11.1. 1 ,II{(111111.1, llll,tt'i cont l.l:t NAS '1 t 1

I^.11 I , 1 t I h t: rt'.11'.11 k , it WA .ltl}`}','t ( 1'.1 I'\' .1 l;r.1111 . Ntil: No. t , .111 . I ,` •t' 1,

St.11t' till Ivor:iit\'.

1 I I 't

. J .. 1 l i ^ ^ ^ ^ 1 t i l l ^1_ _4 - -- 3.

i

References

l .I. Murray and A.F. Renard, Reports "Challrnher" Fxped. 4 (1891) 327.

2 K. Schmidt, NASA TN D-2719 (1965)

3 D.W. Parkin and U. Tilles, Science L54 (1968) 936.

4 H. Millard and R. Ftnkelman, .1. Geophys, Res. 75 (1970) 2125.

5 R. Schmidt and K. Keil, Geochim Cosmochim. Acta 30 (1966) 471.

6 W. 11unter and U. I'arkin, R. Soc. London Proc. 255 (1960) 382.

7 A. Bruun, E. Lanier and H. Pauly. Deep Sea Research 2 (1955) 230.

8 I). Parkin, R. Sullivan and .1. Andrews, Nature 266 (1977) 515.

9 D. Brownlee, The Sea. 7 (1978) (W press).

10 l). Browcalee, I'. Hodge, M. Blanchard, 'r. Bunch and F.T. Kyte, 9th Lunar

and Planetary Science Proe., Ilan. Sci. [-is( . (1978) 126.

11 M. B. Blanchard and G.C. Cunning1kam, J. c-eophvs. Res. 79 (1974) 3973.

12 M. B. Blanchard and A.S. Davis, J. Geohhvs. Res. 83 (1978) 1791.

13 F.'1'. Kvte, ?1.5. Thesis., ,.in .lose State Univ. (1 0 77); also NASA CK 152,075. i^ 14 l). F. Brownlee, D. Tom.ind l , M. B. Blanchard, C.1' . Ferry and F.T. Kvte.

NASA TM \-73,152 (197o ) .

15 M. B. M anchard. J. Geophys. Res. 77 (1972) 2442. f

16 I^. lleezen, 1. MacGregor, H. Foreman, G. Forristall, it. 11okel. K. Hesse.

K. Hoskins, F. Jane,, A. K. ► ncps. A. Krashcnnikov, V. Okada and 11. Ruef,

initial Rvp. p eep Sea Drillin t;I'roj. 20 (1973) 725.

17 R.B. FinktAman, Marine Tech. .1. 6 (1 1)72) 34.

18 R. Castaing and K. Fredrickson, Geochim. CnsmoLhim. Acta. 14 (1958) 114. t 19 It. Fechtig and K. Uteck, Annals New York Acad. Sci. 119 (1064) 243. 1 20 J. Jedwah, Geochim. Cosmochim. Acta, 34 (1970) 447.

1 L) i .' 17

11. Marvin . ► nil M. F Iimu l i . i;vochtin. Cotimoch tin. Av t a 11 ( 14117) 1871 .

.. N. I'. • t 1 , rss% 1 n .nt.i K. Frt • ,tr il.::rwtt, Pa i t it• St. i . 1: l 1 t► ti8) 71 .

' t lt. Fln{.i•In► .n,. St• it • r,t• t • 101 (1')1O) ► ti:

'4 l%. ► :. ► n. ► ll. ► tlty, l ► . Itcowult • r .u ► .1 V. Il,►ttgo. ti, • ionct• (1 11 1ti) tin I+1"r90.

.5 !t.tt. Itl.utrh. ►► ,i. Mctvol iI i,• :► `, (1` ► 10) lt't.

HrowllIvo M. It. t^l,u ► k h.trtl., l:.l:. l'unnln^;h:un, K. ttraut l ► . ► rn{^ .► n.l

K. F1-111 m ' l, .I Kt-!I. 80 (1'1 1 , ) t`► ; i.

1 VoliMi • lt.tvIi:: . ► n,l I \I ► rot► s. t?artII l'l:ll. ors ', (l` ► t+`► 1K1.

t,`)) .'K I.. Ahrt, u:: .u ► ,1 11. von ►I'lirh. ► , • lir:, I.i ► tl, P1.n1. tint. l,ttrrs 'i (1` ►

: y E. AmIt• r:I. K. l:.u ► , ► l,.ttlty, h. hr. ► hrnhultl and ti. Morg.m. The Moon 8 0470 1.

f s P

1

I ^

't l J A J n A A J N J J O D J O O O O .-^ ^ `' `+ Y V V V V M M v O M 00 co n n v'^ n O M ^D N M .D O O .r O J 00 -4 O O .+ 00 M J ,^ A

41

fV O U •r1 ++ u n •-+ O ^n J N 1 C 1 U) O s ro Yl N •.4 I N N O M N ^C+ a w LIS N b a ••r n M p n' M M O O a N O 44^ .-+ t V V O b u a y N 3 I ?, tp a V u * A N u1 O ^p 1 N .p U 1 ti T •.a

in "^ N •-•f G In w O N ^+ A J M J n •H ro N N u a n J N s N O O J+ .r a ro N •C N O rh Y •-•^ O N O ^ .-^ M N o a '', V ^. Ir L Q r-^ o ro u y ^I Li w T fX, O r` J dp ^C N N .--. P_ u N a O r+ O r` N O O 1 a c x N .-r .-r DO /0+ S .1 y U O N N J ^p J^ ON 1-1 N C O s N •-1 C a v M O N 9 M O O O .+ N .1 N N V O .-r C. O am a u a 't7 u t,, M J J ^1 r^ n OD `n fd •rl 0 LA J O O A .--+ O O N 1 N C13 .L1 •L7 y ro N I .^ a ^ r+ N n .--^ M rr M ,4 O Vf - r^ ^D O J O 0 IN •.^ s of %0 O co 3 N a N O O U1 00 ^ .•+ N O .-r .-. ^n N Ln C Q .-^ V a U x .-1 cm •,4 a G H T .0 O V) cti •,^ u u .. m r_ ro a a cr, a N W fr fa. O M M - a ..^ a a 14 r4 a as .-c .c .^ O N N 0 a O O O O 41 w C.) LM z w ^ L) s fn Ho uV •Y. 1 1

^l

T I r

M M ^ N r^ ^ tT N .n M M N ,,,,^ ^ H I M^ O v O O ^ ,O O O O ^T N H of a a S^ y L H a O LO) u

u y ^ ^^ 1 a O N O o0 u ^ ,^ O `O "^ O O O O .Y F, J "^ v p a .r ••+ rtf i/f C 7 ^n •^ w co ^ s M d -S N O .•^ V OC 4J v O O M G .0 M •+ u O O O O O p^ r^ 4. v 8 O+ V ►• y .r u7 wO ...G u O U ^ ac N ^'^^ y ^D J 00 .•^ ^1 O ^ •.Gd .~i Q! y O co N O O •.Gi M N O O ^+ 4 v O ^D DO ..r H US •.y ^ M O as

00 v N ^O C^ u v ^ .-, ^ ^., O y os o o o o u v x u "' O a u y

1+ .-r O ^ ^7 W G1 ^n ^D O r•'+ 00 ai u y ^ oo .o o N o .o ^+ N 1° 1 O in O O O O a ^n v a u U .-ro u 1+ "4 O .-+ w w ^ O 00 .^ M Ln v •o y N O O M O N N N N Q .-1 ^p O N O O O O O^ w u in v O s

C ^ ^ y ►4 1 -o ro v t W ,y N Vf N

CIS G• ^ ^ ro a N «1 ^O O N M I^r ai > u in to y 00 o ^-+ ^o c o c o: o ld Lh /. U G J v •.1 y M^ w ro x x c O u 1 U 4. • 4 C O 0

i to ►+ u "i Ny 4 y W 3 O .a "'^ co 4 N p ^ O O^ O O O u J Lu fjw U :r. E••

2 Ii I

TAN1 F. 3

Averag., ,ibundances of 19 Kilicat, viphores k omhared with urdinar y and cartl.maceous chondr i t os .

Kph.r.w • 1 0 I C2 11 L i

t

Mg/Si 0.8ti2 U. 160 1.U(1 1.0:,6 0.97 0.94

Fc/S1 0.832 ! 0.53: 0.901 0. 84 1 0.812 0.577

Ca/Si 0.0544 0.0267 0.0721 0.0719 0.0448 0.0484

Al/Si 0.07b2 0.0340 0.085 0.084 0.061 0.0(11

Ni/Si 0.0137* 0.051 0.046 0.049 0.030

Cr/Si 0.00825 ! 0.00479 0.0127 0.0124 0.010(1 0.0109

Mn/Si o. 00t)34 0.00332 0.000-1 0.0062 o.Oob8 0.0068

Ti /51 0.00214 s 0.000(14 0.0024 0.0024 0.0021 0. 002 1

*Throe spheres dtd not contain drtoc tod Ni 0-0.02 %.) and this tahlt.

t rv.tt s t h k ui pol limit .tK a m..t::ur. d VA luV.

1

3 -ter-• - - .^*^^^-P-^S ,^ ^w^ ^^^ ' ^ ^ ^^ -?- rr--'^ +-^ ^ jF T ^. ^ ^ ! ^ 1 1 , . M

TABLE 4

Silicate spheres having Ca/A1 ratios between 1.0 and 1.25

compared with mean elemental analyses for H-group and

enstatite chondrites [27.281.

Fe Mg Ca Al Si

Sphere #25 26.0 14.6 1.4 1.2 16.9 I

H-Group Chondrite 27.0 13.9 1.2 1.1 16.7 1 (mean)

Sphere #33 34.7 10.9 0.9 0.9 14.4

Lnstatite Chondrite 29.5 11.5 0.9 0.8 16.8

(mean)

i

j^ 24

l "-1 -,0,7 P"

I •

ORIGINAL PAGE LS OF Po OR QUALITY

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Fig. 2. An SEM image of a silicate sphere with surface etched away by seawater. Aligned olivine and magnetite crystals form brickwork-like patterns produced during ablation. Scale - 25 Jim. 6 1

ORIGINAL PAGE 15 OF POOR OIJALITY

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Pig. Vii. Enlarged area of sphere shown in Fig. 1. large ervstals (gray) are olivine, small (hrig;ht) crystals often connected In chair- Like fashion are magnetite, and groundmass areas are interstitial glass. Slightly above and to the right of the photo center is a hollow olivine crystal which has had its Mg;-rich core dissolved away. Scale = 10 ;im.

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Fig. 15. Data compiled from 19 silicate spheres, comparing the elemental abundances of the spheres (normalized to Si) to the Cl average. The vaiues were obtained on the centers of spheres that did not show apprecia- ble alteration of the glass phase.

A1, Y NG F lb I OK1u1N ^2U ALiTY OF POOR 40 r r

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Fig. 16. Data compiled from hulk analyses of 19 silicate spheres showing the Ca/A1 ratio of the silicate spheres to the Cl (*), li and L (o), and enstatite (n) chondrites. The line is where the ratio of Al/Si to Ca/Si equals one.

41