PARTICLE SI-L<\PES OF THREE LUNAR

SOIL SAMPLES

By

Arshud MatmoodWoodward-McNeill & Associates

Los Angeles, California

James K. MitchellDepartment of Civil Engineering

University of CaliforniaBerkeley, California

and

w. David Carrier, IIIBechtel Corporation

San Francisco, California

I

PARTICLE SHAPES OF THREE LUNAR SOIL SAMPLESby

Arshud Mahmood, James K. Mitchell & W. David Carrier, III

Shape of mineral particles and rock fragments has beenstudied extensively (Wadell, 1935; Krumbien, 1941). The

.particle shape studies being carried out on lunar soil haveexplored some new ways to express shape (Heywood, 1971;Gorz et al., 1971, 1972). In the present study, threesubmillimeter samples of lunar soil were separated intofractions and theij shapes were studied by conventionaltechniques.STUDY TECHNIQUES

Each sample was first wet-sieved with freon to sep-arate it into fractions. Some particles from each fractionwere then spread on a transparent plastic plate and photo:graphed (on slide film) twice--once under direct light,Fig. 1, and then with the light coming from below theplate to form a silhoutte, Fig. 2. The slides of silhouttedsahpes were projected on large paper sheets and the boun-daries were drawn. The length to width ratio was thencomputed by making measurements on these sheets of paper.The silhouttes were also compared with particle shapecharts of Russel-Taylor-Pettijohn (Muller, 1967) , Fig. 3.

'These charts are based onWadell's shape criteria (Wadell, 1935).The photography done under direct light was also on

color slides, and these were projected on a screen for com-

parison with th~ three dimensional shape charts (Powers, 1953),

Page '2

Fig. 4. A brief summary of samples that were studiedis given in Table 1.

RESULTSA) Length to Width Ratio

Particles from several fractions of each sample were

studied. These results are summarized in Table 2. There is no

significant difference between the L/W ratio of various size frac-

tions within each sample. Except two size fractions in sample

14259 (20-40 and 40-100), all other fractions have L/W ratios of

1.3 or over. The number 1.3 is usually considered to be the

boundary between. equant and elongate particles, and most grains in

the lunar soil are, therefore, elongate. A weighted average of the

various fractions is given in Table 3, and it clearl: shows that,

overall, the lunar soil grains are somewhat elongated. The orienta-

tion of long axes would therefore be a significant measure of

fabric. Considerable proportion of grains in each sample was more

elongated than the mean L/tv ratio, Figs.

B) Shape of Silhouttes

The silhouttes of particles were compared with charts to

determine their roundness (as originally defined by Wadell, 1935),

5, 6 and 7.

Table 4. lbese determinations were made on the same drawings

from which Lengths and Widths of grains were measured, and hence

the Per Cent by Weight and Number of Particles values are the same

as in Table 2, and have not been repeated in Table 4.

All fractions of the three samples have very low roundness.

It appears that the roundness values increase somewhat as the

grains become finer. The weighted averages place all three samples.

in the "Subangu Lar" class, Table 5.

I

C) Shape under Direct Light

Grains from each fraction were photographed on color 'slides

and then projected on a screen for viewing and for comparison with

'Powers' charts. Simple averages of the roundness values of grains

in each fraction are given in Table 6. There is no consistent

change in the roundness values with changing grain size.

The weighted averages are given in Table 7, and show that accord-

ing to Powers' classification, all three samples fall under

"Angular".

CONCLUSIONSThe lunar soil grains are somewhat elongated and have a low

roundness. Orientation of long axes of grains is one significant

measure of soil fabric.

I

REFERENCES

Heywood, H. (1971) "Particle size and shape distribution for lunarfines sample 12057, 72", Sec. Lun. Sc. Conf., Geochim.Cosmochim. Acta, Supple 2, MIT Press, Vol. 3, pp. 1989-2002.

Garz, H., White, E. W., Johnson, G. G., Jr., and Pearson, M. W.(1972) "CESEMI studies of Apollo 14 and 15 fines", Proc.Third Lun. Sci. Conf., Geochim. Cosmochim. Acta, Supple 3,Vol. 3, MIT Press, pp. 3195-3200.

G6rz, H., White, E. W., Roy, R. and Johnson, G. G., Jr. (1971)"Particle size and shape distribution of lunar fines byCESEMI", Pro c, Sec. Lun , Scd , Conf ., Geochim. Cosmochim.Acta, Supple 2, Vol. 3, MIT Press, pp. 2021-2025.

Krumbien, W. c. (1941) "Measurement and geological Significance ofshape and roundness of sedimentary particles", J. Sed. Pet.,Vol. 11, pp. 64-72.

MUller, G. (1967) "Methods in sedimentary petrology", Section on:Degree of roundness according to Russel-Taylor-Pettijohn(after Schneiderhohn), pp. 100-101, Hafner, N.Y.

Powers, M. c. (1953) itA new roundness scale for sedimentary particles",J. Sed. Pet., Vol. 23, No.2, June 1953, pp , 117-11.9.

Wadell, H. (1935) "Volume, shape and roundness of quartz particles",J. Geol., Vol. 43, pp. 250-280.

Table 1 Summary of Lunar Soil Samples

Number of Particles StudiedFor L/W For Shape in For Silhoutte

Sample Weight of Sample, g Measurements Direct Light Shape

tc1\f,3 ~, 148)

111259, 3

0.97 249 161161

160 4074071.26

1.5601,82 0.96 568568 232

Table 2 Length to Width Ratio of Lunar Soil Grains

Percent of Sample by Number of ParticlesFraction (Sieve Nos.) Weight Studied Length/Width Ratio

14163 14259 15601 14163 14259 15601 14163 14259 156018-20 2.3 0.7 3.1 10 6 10 1.38 1.38 1.42

20-40 6.1 5.8 6.7 18 11 30 1.35 1.27 1.33 _

40-100 15.7 22.7 23.2 31 37 115 1.34 1.28 1.38

100-200 14.2 11.0 20.2 102 181 146 1.31 1.36 1.42

200-325 12.2 29.9 14.5 - 158 267 - 1.32 1.39

-325 49.5 29.9 32.3. - 14 - - 1.31

, i

Table 3 Weighted Average of Length to Width Ratios

(according to Per Cent of Sample by Weight)

Sample Length/Width Ratio

141631425915601

1. 38

1.311. 39

Table 4 Roundness of Lunar Soil Grains (Wadel!)

RoundnessFraction 14163 14259 15601

8-20 .16 .21 .14

20-40 .17 .21 .14

40-100 .19 .25 .12

100-:-200 .22 .26 .23

200-325 .29 .23

-325 .27

-------------------------

Table 5 Weighted Average of Roundness Values (Wadell)

SampleRoundness

Number Class

14163

14259

15601

.19

.26

.19

Subangular

Sub angular

Subangular

Table 6 Roundness of Lunar Soil Grains (Powers) ,

Percent of Sample by Weight Number of Particles Studied Roundness.Fraction 14163 14259 15601 14163 14259 15601 14163 14259 .·15601

8-20 2.3 0.7 3.1 5 7 7 .20 .18 .20

20-40 6.1 5.8 6.7 36 26 14 .18 .17 .17

40-100 15.7 22.7 23.2· 124 98 75 .19 .21 .20

100-200 14.2 11.0 20.2 44 9 84 .2 .22 .27

200-325 12.2 29.9 14.5 12 - - .2

-325 49.5 29.9 32.3 . 28 20 52 .26 .17 .24

- ----fJ{-[ 1(,0 232-

2.~ '(..1(

Table 7 Weighted Averages of Roundness Values (Powers)

RoundnessSample Number Class

14163 .20 Angular

14259 .25 Angular

15601 .22 Angular

Fig. 1: Photomicrograph of Lunar Soil Grains Under Direct Light,

Sample 14259, 3, Size Fraction Between Sieve Nos. 8-20.

·:~;);~ilF,;ifI?~-'

..".

1/; .", .-~-::

i'~

-.....

Fig. 2 : Photomicrograph of Lunar Soil Grains in Si1houtte~

Sample 14259, 3, Size Fraction Between Sieve Nos. 8-20.

«:t~

ANGULAR

SUBANGULAR

SUBROUNDED

ROUNDED

WELL ROl.JNDED

Fjg. 3: Degrees of Roundness for Mineral Particles Seen inSilhoutte. Based on Wadell's Criteria

(from Muller, 1967)

~----.--

VERYA~NGULp<H ANGULAR

, ' '

"':',WELL';';",~'~.',ROUND'EO'

. ',- . ,- .-,

Fig. 4: Degrees of Roundness for Mineral Particles Seen Under Direct Light, Based on Powers' Criteria(from Powers, 1953)

20 Mean L/W rotio = 1.38

!(/)

~o-\-o

0_-,0\-

W.0

E:::l:2

o-o-..,;.o-cwo\-

&o IlL (' ? L JA. '- L L t.:X L. L /, / B,' L <' L. ,(J' .1'. <. / / If. / / /J at; / / / LK? t' / L (I( ? IJ ? J( { { { / dI

1.0 1.1 1.2 l3 1.4 1.5 1.6' 1.7 1.8 1.9 2.0Length/Width Ratio of Particles'

Fig. 5: Grain Shape Distribution of Lunar Soil Sample 14163, 148Results Based on Study of 159' Particles

"

!.'

201- ~///l Mean L/W ratio = 1.31enQ)

u-h-

·00..-0-0ן

m.0

E::lZ

E 100I--0-cQ)0•...Q.)Q.

o r / / / /V.•.4/ / i' /.( / (i ( / / / " / L.I-4!1/ / L L rr L / WI / / ( {i'.I. ?, ?, OC < < ( 'LI

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 -

Fig. 6: Grain Shape Distribution of Lunar Soil Sample 14259, 3Results Based on Study of 406 Particles

20. -en

'~

.~-"-aQ.

\6-

0

"-Q).0

E::>2 10004-

~\6-

0.•..e(\.)

0"-OJa.

01.0

L/W ratio =1.39

1.1 . 1.2 1.3 1.4 1.5 1.6 1.7 1.8Length/Width'Ratio of Particles

1.9 '2.0

Fig. 7: Grain Shape Distribution of Lunar Soil Sample 15601, 82Results Based' on Study of 561 Particles

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