Petrology and Stratigraphy of 

the Fra Mauro Formation at 

the Apollo 14 Site 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 785 

Prepared on behalf of the 

National Aeronautics and Space Administration 

Petrology and Stratigraphy of 

the Fra Mauro Formation at 

the Apollo 14 Site 

By H. G. WILSHIRE and E. D. JACKSON 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 785 

Prepared on behalf of the 

National Aeronautics ancl SjJace Acl1ninistration 

Dish·ibution of Apollo 1-1 fragn1ental rocks, 

classified into four groups, suggests that 

the Fra Mau.ro Fonnation consists of 

sh·atifiecl ejecta 

UNITED STATES GOVERNl\1ENT PRINTING OFFICE, WASHINGTON 1972 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 72-600103 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 
CONTENTS 

Page 

Abstract ____________________________________________________________________________________ _ 1 Thin-section petrology- Continued 

Introduction ______________________________________________________________________________ _ 1 Matrix materials _____________________________________________________________ _ 

Returned samples ____________________________________________________________________ _ 2 Matrix-clast reactions ____________________________________________________ _ 

Megascopic structures ____________________________________________________________ _ 4 Partial fusion ___________________________________________________________________ _ 

Hand-specimen petrology _______________________________________________________ _ 4 Deformation of mineral and lithic clasts ____________________ _ 

Homogeneous crystalline rocks _____________________________________ _ 5 Compound clasts---·-------------------------------------------------------··-· 

Fragmental rocks ____________________________________________________________ _ 5 Classification of the rocks ______________________________________________________ _ 

Thin-section petrology ____________________________________________________________ _ 6 Rock distribution _____________________________________________________________________ _ 

Glass clasts _______________________________________________________________________ _ 7 Fra Mauro Formation ____________________________________________________________ _ 

Mineral clasts ___________________________________________________________________ _ 7 Conclusions _______________________________________________________________________________ _ 

Lithic clasts ______________________________________________________________________ _ 9 Fra Mauro Formation ____________________________________________________ _ 

Igneous rocks ____________________________________________________________ _ 9 Pre-Imbrium terrane ______________________________________________________ _ 

Metamorphic rocks __________________________________________________ _ 11 References cited .. ·----·--··-·········------------······-······························· 

ILLUSTRATIONS 

FIGURE 1. Regional geologic map of the area surrounding the Apollo 14 landing site __________________________________________________________ _ 

2. Map of major geologic features in the Apollo 14 traverse area ________________________________________________________________________________ _ 

3. Surface photograph and photomicrographs of Apollo 14 rocks _________________________________________________________________________________ _ 

4. Scheme used for subdivision of Apollo 14 rocks ... ----------------------------------------------------------------------------------------------·-··--------· 

5. Frequency distribution of clasts >1 mm in fragmental rocks of groups F 1, F::?, F3, and F4-------------------------------

6. Histograms showing relative abundance of glass, mineral, igneous, and metamorphic clasts 

Page 

15 

16 

17 

17 

17 

19 

21 

22 

23 

23 

24 

25 

Page 

2 

3 

4 

5 

6 

and microclasts in the fundamental rocks of groups F 1, F 2 , F 3, and F4--------------------------------------------------------- 8 

7. 

8-11. 

Triangular plot of plagioclase-pyroxene-olivine microclasts________________________________________________________________________________________ 9 

Photomicrographs of Apollo 14 rocks·------------------------------------------------------------------------------------------------------------------·10, 13, 14, 18 

TABLE 

12. 

13. 

Triangular plots of clasts and microclasts of glass, igneous, and metamorphic rocks___________________________________________ 20 

Distribution of fragmental rock types at the Apollo 14 landing site_______________________________________________________________________ 22 

14. Map showing outer mountain rings of major lunar basins, their relative ages, and the 

extent of their continuous ejecta blankets--------------------------------------------------------------------------------------------·------·-··--------

TABLES 

1. Classification of rocks larger than 1 gram .. -------------·----------------------------------------------------------------------------·--------·--·--·--------·--· 

2. Principal types of clasts and microclasts---------------------------------------------------------------------------------------------··------····-·········---·-·· 

3. Clast sizes and grain sizes of some igneous clasts.--------------------------------------------------------------------··------·-··-----·----------------· 

4. Modal compositions of basalts·------------------------------------------------------------------------------------------------------------------------------------------· 

5. Types of vitrophyres·------------------------------------------------------------------------------------------------------------·---------------------------------------·-----· 

6. Modes and average grain sizes of common cumulates·------------------------------------------------------------------------------------------------··· 

7. Distribution of mineral reactions.-----------------·---------------------------------------------------------------------------·-·------··-----------·-···--··--------· 

8. Clasts and matrix types in compound clasts·------------------------------------------·-----------------------------------------------------------------------· 

III 

25 

Page 

5 

7 

9 

9 

11 

11 

16 

19 

PETROLOGY AND STRATIGRAPHY OF THE FRA MAURO FORMATION 

AT THE APOLLO 14 SITE 

By H. G. \VILSHIRE and E. D. JACKSON 

ABSTRACT 

The Apollo 14 rocks returned to earth are divisible into two 

broad groups: relatively homogeneous crystalline rocks and 

fragmental rocks (breccias). The crystalline rocks are, for 

the most part, metaclastic, but a few, including the second 

largest sample returned, are aphyric basalts. All of the crystalline rocks are considered to be clasts dislodged from fragmental rocks. These fragmental rocks constitute the Fra 

Mauro Formation, which is presumed to be the ejecta deposit 

from the Imbrium basin. Megascopic properties of the fragmental rocks suggest a fourfold subdivision: Ft, poorly consolidated breccias with light clasts dominant over dark ones, 

with few clasts larger than 1 mm, and with comparatively 

abundant fragmental glass; F2 , coherent breccias with light 

clasts dominant and with comparatively abundant fragmental 

glass; Fs, moderately coherent breccias with dark clasts dominant and with no fragmental glass; and F 4, coherent breccias 

with dark clasts dominant and with no fragmental glass. 

Systematic microscopic descriptions and clast counts of 

19 different breccias revealed that (1) clasts of fine-grained 

thermally metamorphosed fragmental rock are by far the 

dominant type in the breccias; (2) there are eight main 

varieties of igneous clasts including basalt, anorthosite-gabbro, plagioclase cumulates, and quartz-alkali feldspar intergrowths; ( 3) a significantly high proportion of mineral 

clasts occurs in the size range 0.1-1.0 mm; plagioclase is 

dominant among the mineral clasts, but the proportion of 

pyroxene is as much as 50 percent; and (4) lithic and 

mineral clasts commonly are cataclastically deformed. 

Most of the rocks contain compound clasts that are themselves pieces of breccia. Two generations of breccia are common, and as many as four occur in the samples studied. The 

rock types in compound clasts reveal earlier fragmentationmetamorphic episodes that predate the Fra Mauro Formation. 

Partial to complete reequilibration reactions have taken 

place between matrices and clasts in a number of the fragmental rocks. These relations suggest postconsolidation 

thermal effects on the Fra Mauro Formation. Similar 

reactions are observed within clasts in all types of fragmental rocks, whether glassy or crystalline. It appears 

that more than one generation of reequilibration reactions 

is represented in the Fra Mauro and that older breccias 

had thermal histories similar to that of the Fra Mauro 

Formation itself. 

The distribution of rocks at the Apollo 14 site suggests 

that the Fra Mauro Formation is stratified; units of darkclast-dominant breccias (F3 , F 4 ) are deepest, and units of 

light-clast-dominant breccias ( F 2 ) are shallowest. Poorly 

consolidated glass-rich rocks (F1 ) are considered to be 

weakly lithified regolith, derived either from disaggregated 

F1 type breccias or from originally unconsolidated material 

at the top of the Fra Mauro Formation. This stratigraphic 

sequence is consistent with the comparative abundance of 

glass and the weakly developed reequilibration reactions in 

F2 rocks and with the dominance of light-colored metaclastic 

rocks among the lithic fragments of the soils. It is presumed 

that thermal blanketing of the lower dark-clast-dominant 

breccias allowed time for reactions to proceed ami for annealing and devitrification of glass. Thus, although we see that 

the Fra Mauro Formation is composed of three or four 

distinct units based on clast populations, its internal thermal 

metamorphism appears to be gradational. 

The compound clasts and great variety of lithic fragments indicate that the pre-Imbrium terrane, presumed to 

have existed prior to about 3.9-4.2 billion years ago, was 

already exceedingly complex. However, the similarity of 

older breccias to the Fra Mauro breccias themselves indicates that processessuch as extrusion of basalt, intrusion 

and differentiation of basaltic magma, impact brecciation, 

and metamorphism prior to the Imbrium event were not unlike later events. The complex clasts of the Fra Mauro 

breccias therefore reveal a long history of impact-related 

events that probably record half a billion years of planetary 

accretion, of which the Imbrium impact was one of the last 

large events. 

INTRODUCTION 

Apollo 14 landed on an area of lunar terra composed 

of materials that premission studies indicated were 

ejecta from the Imbrium basin (Gilbert, 1893; Swann 

and others, 1971; Swann and Field Geology Team, 

1971). This deposit, forming a broad belt surrounding 

Mare Imbrium, has been designated the Fra Mauro 

Formation (Eggleton, 1963; Wilhelms, 1970). The 

landing site (fig. 1) is about 550 km (kilometers) 

south of Montes Carpathus, the southern boundary of 

the Imbrium basin, and 150 km north of the mapped 

edge of the ejecta deposit. The formation in this area 

is estimated to be about 500 m (meters) thick (Eggleton, 1963). The principal objective of Apollo 14 was 

to sample the Fra Mauro Formation in the area immediately west of Cone crater, a young blocky crater 

superposed on a ridge of the formation (fig. 2). Cone 

crater was presumed to have excavated Fra Mauro 

material from beneath the local regolith, making about 

1 
2 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

the upper 75 m of the formation accessible to sampling, description, and photography. 

Results of the preliminary geologic investigations 

of the site (Swann and Field Geology Team, 1971) 

and of the preliminary examination of samples (Lunar 

Sample Preliminary Examination Team, 1971) have 

been published. This paper ( 1) presents a general 

report on the petrology and petrography of the Apollo 

14 samples, based on our examination of the textures 

and structures of the rocks in hand specimen and thin 

section, (2) classifies these rocks, and insofar as is 

possible at this time, (3) discusses the stratigraphy 

and origin of the Fra Mauro Formation. 

Acknozuledgments.- This work was done under 

NASA contract T -4 738A. We are much indebted to 

J. P. Lockwood and D. J. Milton, U.S. Geological Survey, for critical review of the manuscript. 

RETURNED SAMPLES 

Apollo 14 returned about 43 kg (kilograms) of rock 

samples, of which 321 specimens weigh more than 

50 g (grams) and 1241 specimens weigh more than 

1 g (Lunar Sample Preliminary Examination Team, 

1971). These samples were collected by Astronauts 

Mitchell and Shepard during two traverses covering 

a distance of about 3,175 m (Swann and Field Geology Team, 1971) . The location of samples along the 

traverses is known for the majority of rocks; two 

rocks bigger than 50 g (14303, 14169) are still only 

tentatively located (Sutton and others, 1971). 

In contrast to rocks returned by Apollo 11 and 12, 

the. Apollo 14 rocks are predominantly fragmental and 

consist of clasts ( > 1 mm) (millimeter) and microclasts (0.1-1.0 mm) in fine-grained matrices. Indeed, 

only two of the 32 rocks weighing more than 50 g and 

a correspondingly small proportion of the 124 rocks 

weighing more than 1 g are homogeneous crystalline 

rocks (Lunar Sample Preliminary Examination Team, 

1971). The homogeneous crystalline rocks all have 

their counterparts as clasts in fragmental rocks (Lunar Sample Preliminary Examination Team, 1971). 

One san1ple ( 14053) was collected from the side of a 

boulder, and surface descriptions by the Apollo 14 

crew indicate that it was a clast in a fragmental rock 

(Sutton and others, 1971). The other (14310) is considerably smaller than the largest clast observed in 

surface photographs and is lithologically identical to 

clasts in returned fragmental rocks. It appears likely, 

therefore, that all the homogeneous crystalline rocks 

are clasts that were dislodged from fragmental rocks, 

either on the lunar surface by natural processes or by 

handling after collection. 

1Totals combine samples that were broken by handling but that were 

given different Lunar Receiving Laboratory numbers (Swann and Field 

Geology Team, 1971). 

EXPLANATION 

Materials of maJor postFra Mauro craters 

Dark mantling matenal 

Young mare basalt 

Old mare basalt 

Pre-mare platns- forming 

material 

Alpes Formation 

Fra Mauro Formation 

Materials of 

-

mountains rimming the Imbrium Basin 

Undivided terra materials 

J!ostly pre-Fra /l,faum materials, hut includes some later 

crater deposits and prohahle 

l'olcanic rocks 

FIGURE 1.- Regional geologic map of the area surrounding 

the Apollo landing site. From Swann and Field Geology 

Team (1971). 
Continuous ejecta blanket Boulder ray deposits 

Material of Cone Crater 

Smooth terrain material of 

the Fra Mauro Formation 

0 

Ridge material of the 

Fra Mauro Formation 

100 

RETURNED SAMPLES 

0 

EXPLANATION 

Contact 

/,ong dashed where approximately located: short dashed where location is 

inferred without local evidence 

-x---

Foot of scarp 

Bounds small meso. Short dashed where 

location inferred Triangles point down 

slope 

----z;----?'S:--75,--

Edge of hill 

Long dashed where approximately located: short dashed where location inf erred. Triangles point down slope 

500 METERS 

Traverse route for 

EVA's I and 2 

Stations 

oB -Panorama station 

~:~ G 1 -Station without panorama 

C/S -A LSEP Central Station 

3 

L R 3 -Laser Ranging Retroreflector 

Samples 

FSR -Football size rock 

eCont - Contingency sample Spl 

eCom1 P-Comprehensive sample Sp 

Dg -Grab sample at Station D 

FIGURE 2.- Map of major geologic features in the Apollo 14 traverse area. From Swann, Trask, Hait, and Sutton (1971). 
4 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

MEGASCOPIC STRUCTURES 

Swann and Field Geology Team (1971) and Hait 

( 1972) provided descriptions and detailed maps of 

the internal structures in some large boulders photographed by the astronauts. The main types of 

megascopic structures, besides the obvious fragmental 

textures, are fractures, color layering, lineation or 

foliation, and veins. The fractures occur in multiple 

sets of generally planar, parallel joints spaced from a 

few millimeters to a few centimeters apart. Color layering is particularly well developed in boulders from 

the area near the "white rocks" (fig. 3A), where 

prominent white-gray layers about 1 m thick occur. 

In places, soft layers are etched into depressions, presumably by micrometeorite scrubbing, while adjacent 

harder layers stand out as ribs. Some layering in essentially monotoned boulders is defined by differences in 

sizes of clasts from layer to layer; size layering also 

accompanies the color layering. Some layers have 

highly irregular contacts, whereas others are nearly 

plane parallel. There appear to be sizable discordances 

in attitude between sets of layers within two boulders 

(Hait, 1972), and in places, layers are contorted. 

Rarely, a weak lineation or, more probably, foliation 

is produced by alinement of lenticular clast-s, and one 

irregular white layer about 1 em (centimeter) thick 

in Weird Rock (Swann and Field Geology Team, 

l 971) may be a vein. 

Features of this kind are, of course, less obvious in 

the smaller returned hand samples. Many rocks, including 14304, 14302-14305, 14312, and 14313 have 

shapes ,partly controlled by fracture sets, and a number, including 14306 and 14316, are cut by glassy 

veins. Sample 14082, collected from one of the "white 

rocks," is layered (fig. 3B, C) with millimeter- to 

centimeter-thick irregular units differentiated by the 

abundance of darker clasts and by average size of 

debris in the matrix (fig. 3C). Samples 14076 and 

14453 are also layered fragmental rocks. Sample 14076 

has an irregular but sharp contact separating rock 

with about 30 percent clasts from rock with 5 percent 

of the same types of clasts. Sample 14453 consists of 

light- and dark-colored laminae of fragmental material 

interlayered on a scale of 1-3 mm. 

HAND-SPECIMEN PETROLOGY 

One of-us (Jackson) was a member of the Apollo 

14 Lunar Sample Preliminary Examination Team 

(LSPET) ; the other (Wilshire) was a representative 

of the Apollo 14 Lunar Geology Investigation Group 

to the LSPET. Together, we had the opportunity to 

examine 107 Apollo 14 hand samples larger than 1 g, 

mostly with the aid of binocular microscopes. Many 

of our descriptions were systematized by using a form 

that required notation of a wide variety of features 

FIGURE 3.- Surface photograph and photomicrographs of 

Apollo 14 rocks. A, NASA photograph AS14- 68-9448 showing complexly. interlayered light and dark rocks in block 

near rim of Cone crater. Both rock types appear to be 

fragmental. Bar scale 2 m long. B, Photomicrograph of layering in sample 14082,11. Plane polarized light view showing planar contact between a layer lacking dark clasts 

and one containing them. Bar scale 1 mm long. C, Same 

area as 38, crossed nicols. Layer lacking dark clasts has 

a coarser grained matrix. Bar scale 1 mm long. 

for each specimen. Structures, textures, and lithologic 

properties, such as degree of induration, grain size, 

and mineral proportions, were systematically described 

and measured. This information is presented here because wide access to the hand specimens is no longer 

possible and because the broad petrologic framework 

required for classification and stratigraphic studies 

could not otherwise be established. 

The Apollo 14 rocks may be divided into two broad 

groups (fig. 4) : relatively homogeneous crystalline 

rocks and fragmental rocks (or breccias). Both groups 
HAND-SPECIMEN PETROLOGY 5 

Homogeneous 

crystalline rocks 

/ "'-

Basaltic (B) Metaclast1c (C) 

II 

ol 

o I ':rl 

~ I 

~I 

g I 

Fragmental rocks 

~ l _____________ _ Light Dark 

Clast color 

FIGURE 4. - Scheme used for subdivision of Apollo 14 rocks. 

have been subdivided on the basis of megascopic features described below. In table 1, all specimens weighing more than 1 g have been classified into one of 

six categories- two groups (B, C) representing subdivision of the crystalline rocks, and four (F1-F4) 

representing subdivisions of the fragmental rocks. 

HOMOGENEOUS CRYSTALLINE ROCKS 

Group B (basaltic) rocks are even grained and 

aphyric, with textures ranging from intersertal to 

ophitic. Grain size varies from fine to medium, but 

most are conspicuously coarser than the metaclastic 

rocks. Two groups are recognized, one having about 

40-50 percent plagioclase (14053, 14071, 14074) and 

the other having about 60-70 percent plagioclase 

(14073, 14078, 14079, 14276, 14310). Rock 14310 

has small cognate inclusions that are mainly finer 

grained than the body of the rock but are modally 

similar to it (Melson and others, 1972). Clasts of 

basaltic rocks are widespread though not abundant in 

the fragmental rocks. Most of these rocks are richer 

in plagioclase, poorer in ilmenite, and have much 

lighter colored pyroxenes than the basaltic rocks returned by Apollo 11 and 12. 

Group C (metaclastic) rocks have granular textures 

and are fine grained to aphanitic. The rocks are typically inequigranular, with 1-5 percent of irregular 

large mineral grains, usually plagioclase, but less commonly olivine or pyroxene. Both light and dark rocks 

of this type are very common as clasts in the fragmental rocks. All but two rocks in this group are light 

colored and consist principally of plagioclase and 

light-gray pyroxene. The two dark rocks (14006, 

14440) are aphanitic and of unknown mineral composition. These rocks are similar to the common breccia clasts. 

FRAGMENTAL ROCKS 

The fragmental rocks, like the crystalline rocks, are 

distinctly different from those returned by the Apollo 

11 and 12 missions. Most are coherent, contain less 

glass, and have larger and more abundant clasts than 

the fragmental rocks of earlier missions, but a few 

are more friable and contain fewer and smaller clasts 

TABLE 1.-Classification of rocks za,·ger than 1 gram1 

Sample 

No. 

14041 * 

14042* 

14043* 

14045* 

14047 

14049 

14055 

14053 

14071 

14072 

(B) Homogeneous crystalline rocks, basaltic 

Sample No. 

14073 14078 14074 14079 14276 

14310 

(C) Homogeneous crystalline rocks, metaclastic 

14006 

14068 

14069 

14070 

Sample No. 

14077 14434 

14274 14436 14429 14440 

14431 14443 

14444 

14451 

(FI) Fragmental rocks, light clasts dominant, matrix friable 

Percent Percent Percent Percent clasts Sample clasts Sample clasts Sample clasts >1mm No. >1mm No. >1mm No. >1mm 

2 14056 2 14177 1 14427 1 10 14057 1 14178 10 14432 2 ? 14058 20 14185 ? 14437 1 1 14059 1 14250 10 14438 1 3 14061 ? 14251 1 14442 1 1 14062 1 14282 1 14449 10 5 14080 1 14286 5 14452 1 

(F~) Fragmental rocks, light clasts dominant, matrix coherent to moderately coherent 

Percent Percent Percent Percent Sample clasts Sample clasts Sample clasts Sample clasts No. >1mm No. >1mm No. >1mm No. >1mm 

14007 25 14269 10 14281 40 14315 20 14051? 1 14271 1 14285 10 14316 20 14195 1 14272 1 14288 25 14317 10 14201 10 14273 1 14294 10 14318 30 14255 2 14275 10 14297 10 14430 20 14265 10 14277 10 14301 18 14453 1 14267 10 14278 20 14307 20 14268 10 14280 40 14313 5 

(F3) Fragmental rocks, dark clasts dominant, matrix friable 

Percent Percent Percent Percent Sample clasts Sample clasts Sample · clasts Sample clasts No. >1mm No. >1mm No. >1mm No. >1mm 

14063 23 14082* 10 14171 30 14426 5 14064 40 14083* 15 14196 10 

(F.) Fragmental rocks, dark clasts dominant, matrix coherent to moderately coherent 

Percent Percent Percent Percent Sample clasts Sample clasts Sample clasts Sample clasts No. >1mm No. >1mm No. >1mm No. >1mm 

14066 25 14179 20 14266 25 14308* 20 14075 5 14180 1 14270 ? 14309 20 14076 5 14181 50 14279 1 14311* 20 14169 25 14182 5 14296 15 14312 45 14170 5 14188 5 14302* 28 14314 25 14172 6 14194 8 14303 28 14319 35 14173 20 14197 20 14304 25 14320 13 14174 10 14199 20 14305* 23 14321 30 14175 1 14264 10 14306 15 14445 15 14176 1 

Samples lacking sufficient information for certain classification 

Sample 

No. 

14008 

14060 

14198 

Tentative 

identification 

*Identifies broken pieces of same sample: 14041, 14042, 14043, 14045 parts of same sample; 14302, 14305 parts of same rock; 14308, 14311 parts of same rock; 14082, 14083 parts of same rock. 1For location see Swann and Field Geology Team (1971); for weight see Apollo 14 lunar sample information catalog, NASA TMX-58062. 

than most Apollo 11 and 12 breccias. We have distinguished four groups of fragmental rocks on the 

basis of proportions of light and dark lithic fragments 

and matrix coherence. All four groups of fragmental 

rocks are polymict and contain clasts ranging in shape 

from angular to subrounded. 

Group F 1 rocks are defined as fragmental rocks containing leucocratic lithic clasts in excess of mesocratic 
6 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

and melanocratic lithic clasts and having friable matrices. There are 25 rocks in this category ranging in 

weight from 1.5 to 242 g (table 1). In more than half 

of these rocks, leucocratic clasts make up more than 

90 percent of total number of clasts larger than 

1 mm. ~ The abundance of clasts in these rocks is low 

(fig. 5). The majority of the clasts are lithic crystalline very fine grained feldspar-rich rocks; many appear to have originally been fragmental. Angular glass 

fragments, broken spheres, and spheres, mostly medium brown, are common. Mineral fragments larger 

than 1 mm are rare. The matrices of these rocks are 

medium gray and, down to the limit of resolution, 

consist of the same materials as the clasts, but with 

much larger proportions of glass and mineral fragments. Many of these rocks may be weakly indurated 

regolith. 

Group F:.! rocks are defined as fragmental rocks containjng leucocratic clasts in excess of the total of 

mesocratic and melanocratic clasts and having moderately coherent to coherent matrices. There are 30 

rocks in this category ranging in weight from 1.5 to 

1,360 g (table 1). In about 60 percent of these, leucocratic clasts make up n1ore than 90 percent of total 

number of lithic clasts larger than 1 mm. The abundance of clasts is much greater than in F 1 rocks 

(fig. 5); nearly 80 percent ofF:.! rocks contain 5 percent or more clasts greater than 1 mm. The majority 

of the clasts are lithic, and most of them are megascopically indistinguishable from those in group F 1 • 

Clasts of basaltic rock very similar to those of group 

B are present. Very fine grained melanocratic clasts 

that characterize groups F:l and F-1 fragmental rocks, 

while never dominant, are present in many F:.! rocks. 

A few small clasts of finely granular nearly pure 

olivine and pyroxene aggregates are present in some 

F:.! rocks. Mineral fragments larger than 1 mm are 

rare, and glass clasts are distinctly less abundant than 

in group F 1 rocks. Matrix colors range from light to 

dark gray. Mineral fragments are more abundant 

than lithic fragments in the size fraction smaller than 

1 mm. 

Group F~ and F 4 rocks are defined as fragmental 

rocks containing melanocratic and mesocratic fragments in excess of leucocratic clasts. The groups are 

further subdivided on the basis of matrix coherence: 

group F 3 rocks have relatively friable matrices, and 

F 4 rocks are moderately coherent to coherent. So defined, group F 3 contains only six rocks, all relatively 

small. Two of these rocks (14082, 14083), the "white 

rocks," appear to be unique, but 14063 and 14064 also 

2

Most of the breccias have seriate fragment sizes. We arbitrarily subdivide 

these as "clasts," >I mm, and "microclasts," 0.1-1.0 mm. "Matrix" refers 

to glass and fragmental material <1 mm. 

20 

15 

10 

>- 5 

u 

z 

w 

::::> 

d 

w 0 (( 

lL 

(( 20 w 

C) 

:::?: 

::::> 

z 

15 

10 

5 

0 

5 25 45 5 25 45 

PERCENT CLASTS 

FIGURE 5.- Frequency distribution of clasts >1 mm in fragmental rocks of groups F 1 , F2, F3, and F 4 • 

have light-colored matrices. The "white rocks" owe 

their light color to the matrix material, but clasts 

larger than 1 mm are dominantly melanocratic. The 

F4 category contains 35 rocks, the largest weighing 

nearly 9 kg (table 1). Clasts larger than 1 mm are 

abundant (fig. 5). The majority of the clasts are lithic 

crystalline aphanitic dark-gray to black rocks, many 

with metamorphic textures. Leucocratic clasts apparently like those of group F 2 are present but not dominant. Basaltic rocks similar to those of group B are 

present in some rocks, and clasts of granular olivine 

and pyroxene aggregates seem to be more abundant 

than in group F ~· The matrices vary in color from 

light to medium gray. 

Almost all the samples can be classified according 

to the scheme described above. Among several specimens, however, that have noteworthy macroscopic 

features in addition to the characteristics used in 

the classification are glass-cemented breccias (14080, 

14251, 14307), a single fragment largely composed 

of metal (14286), and a single small glass sphere 

( 14425). 

THIN-SECTION PETROLOGY 

Thin sections of only 30 of the samples examined 

megascopically are available. We studied 200 thin sec-
THIN-SECTION PETROLOGY 7 

tions of these 30 rocks. Clasts that could be identified 

as such in individual thin sections of fragmental rocks 

were divided into glass, mineral, and igneous and 

metamorphic lithic types. These groups were further 

subdivided into a total of 22 recognizable clast types 

and several subtypes based on mineralogy, color, and 

texture. (See table 2 for list of types.) The generally 

small size of the thin sections often did not allow good 

statistical results to be obtained for clasts larger than 

1 mm. Accordingly, counts were also made of fragmental material in the size range 0.1-1.0 mm, which 

we refer to here as "microclasts." Systematic microscopic descriptions and counts of clast types of 19 

different fragmental rocks were made from 89 thin 

sections. Counts of 100 clasts and microclasts were 

generally made, although for some samples as many 

as 215 were systematically described and for others 

the lack of thin sections resulted in counts of as few 

as 15. A total of more than 3,000 clasts and their 

individual dimensions were thus identified. The results 

of these clast counts are given below. 

TABLE 2.- Principnl types of clnsts nnd microclnsts 

Identifying 

symbols 

Al--

A~-------------------

B1--

Clast-m icroclast 

type 

________ Pale-yellow to brown glass. 

_______ Colorless glass. 

__ Plagioclase. 

B:!----- ------------------------- _______________ Clinopyroxene. 

B:l--··················---·--··········--········--··Olivine. 

B.t··················--···············-······--··-···Orthopyroxene. 

B~·--···········---------····------··-·····-------···Opaque minerals. 

Cl·-·······················--- .................... Intersertal basalt. 

C2·················································. Ophitic basalt. 

C~----·················---········-·--··········---- Intergranular basalt. 

c4·················································· v ariolitic basalt. 

C:i···-·····--···············-···········-·--········Vitrophyric basalt. 

C6 .................................................. Graphic quartz-alkali feldspar. 

c, .................................................. Plagioclase, orthopyroxene 

cumulates. 

Cs .................................................. Hypautomorphic gabbro, norite. 

Dl······················· ........................... Recrystallized plagioclase. 

D2 ................................................. Light-colored metaclastic rock. 

Da .................................................. Metabasalt. 

D4 .................................................. Dark-colored metaclastic rock. 

D:; ................................................. Recrystallized olivine. 

Dr; .................................................. Recrystallized pyroxenecs. 

D7 .................................................. Metagabbro. 

The problem of differentiating the matrices of the 

fragmental rock proved more difficult. In general, the 

finer component clown to the limits of microscopic 

resolution consists of the same constituents as the 

clasts, progressively clisaggregated as the grain size 

decreases. Much material, however, cannot be resolved 

optically. In some rocks, postconsolidation metamorphism has further affected the compositions and textures of the matrices (Wilshire and Jackson, 1972; 

Warner, 1972). 

GLASS CLASTS 

Two varieties of glass clasts (class A, table 2) were 

distinguished optically: ( 1) pale-yellow to dark-brown 

glass that usually contains mineral and lithic debris 

and that commonly contains newly formed crystallites 

(type A1 ) ; and colorless glass lacking both inclusions of rock debris and crystallites (A:!). Glass clasts 

( > 1 mm) are proportionaUy less abundant than 

n1icroclasts (0.1-1.0 mm) in the total clast population 

(fig. 6). Most glass clasts and microclasts are irregular, angular fragments that were clearly solid when 

incorporated in the fragmental rocks. Some, however, 

have shapes suggesting that they were soft and were 

deformed during their incorporation. Spheres and 

pieces of spheres of both yellow-brown and colorless 

glass occur sparsely. The colorless glass may largely 

be shocked plagioclase (maskelynite); the more comn1on colored glasses probably have the wide range of 

basaltic compositions reported for glasses in Apollo 14 

soils (Jakes and Reid, 1971; McKay and others, 1972; 

Chao and others, 1972 ; Carr and Meyer, 1972) . 

MINERAL CLASTS 

Mineral fragments (class B, table 2) make up a 

sizable proportion of microclasts in all the fragmental 

rocks but, as might be expected, are proportionally 

more abundant in the 0.1- to 1.0-mm-size fraction than 

in the > 1.0 mn1 fraction (fig. 6). A small percentage, 

however, attain sizes as large as 2.5 mm. Plagioclase 

(B1 ) is clearly the dominant mineral clast (fig. 6), 

but proportions of pyroxene are as much as 50 percent 

(fig. 7). A few plagioclase grains appear to have been 

compositionally zoned along irregular boundaries and 

subsequently broken across the zones. Pyroxene clasts 

include pale-brown to colorless augite (B2), nearly 

colorless pyroxene with low birefringence and inclined 

extinction (presumed to be pigeonite, but not differentiated from augite in the counts), and orthopyroxene 

(B4 ). Orthopyroxene clasts, especially the large ones, 

commonly contain exsolution lamellae of clinopyroxene 

(Papike and Bence, 1971) ; the clinopyroxenes are 

commonly, but not always, slightly more abundant 

than the orthopyroxene (fig. 6). Olivine (B3) is present sparsely as mineral clasts as large as 2.3 mm. 

Optical properties and preliminary electron microprobe data indicate that it is typically very magnesian. 

Minor constituents of the mineral microclast fraction (Br;) include ilmenite, metallic iron, troilite, chromian spinel, ulvospinel, native copper, armalcolite, 

zircon, apatite, and potassium feldspar ( ?) (Lunar 

Sample Preliminary Examination Teall!, 1971). In 

addition, we have observed quartz and a dark-green 
8 

A 8 

PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

F1 

:14042: 

.1-1 : 

0 

A 8 C 0 

F2 

A 8 C 0 

:14082:{LT) 

: .1-1 : 

I I 

i 14082i{DK) 

': .1-1 ' 

12;12345ii234S678ii234S678 

A 8 C 0 

F3,4 

:14303: 

i .1-1 ' 

>1 

>1 

14308: 

.1-1 : 

>1 

>1 

A 8 C 0 

FIGURE 6.- Histograms showing relative abundance of glass (A), mineral (B), igneous (C), and 

metamorphic (D) clasts (>1 mm) and microclasts (0.1-1.0 mm) in the fragmental rocks of 

groups F1, F2, Fa, and F 4· 
THIN-SECTION PETROLOGY 9 

81-83- 82+4 

.1-1 mm 

Plagioclase 

82+4 Clinopyroxene 

+ Orthopyroxene 

FIGURE 7.- Triangular plot of plagioclase ( B1) -pyroxene-

( B~+B ) -olivine ( B3) microclasts. 

amphibole ( ?) (thin section 14308,2) in some thin 

sections. 

LITHIC CLASTS 

IGNEOUS ROCKS 

Nine varieties of igneous rocks occur as clasts and 

microclasts (table 2) : five textural variants of largely 

crystalline basalt, vitrophyric basalt (five subtypes), 

graphic intergrowths of quartz and alkali feldspar, 

cumulates (seven subtypes), and hypautomorphicgranular rocks (two subtypes). Despite the considerable variety of lithologies, clasts of igneous rock are 

not particularly abundant among the lithic clasts as 

a whole (fig. 6). 

The most abundant igneous rock type is aphyric 

intersertal basalt ( C1) . Clast sizes in thin section are 

as large as 6 mm (table 3), but rock 14310, inferred 

to be a clast, is of this type and measures about 18 em 

TABLE 3.- Clast sizes and g-rain sizes of some igneous clasts 

Group 

(table 2) 

Maximum 

clast size 

in thin section 

(mm) 

6 

5 

4 

4 

4 

2 

2 

7.5 

Average 

grain size (mm) 

0.03-0.08 

.1 - .2 

.05 

.1 - .2 

.5 - .6 .05- .13 

.2 -3.0 

(centimeters) across. The majority of these rocks are 

somewhat finer grained than 14310, but 14310 is texturally inhomogeneous (Ridley and others, 1971; Melson and others, 1972) on a scale comparable to or 

larger than the average clast size of the basalts (fig. 

8A). Rocks with intersertal texture are rich in plagioclase (table 4), which typically forms slender euhedral 

crystals interspersed with subhedral clinopyroxene. 

Opaque minerals (ilmenite, troilite, metallic iron) are 

present in small amounts (table 4). The groundmass, 

ranging from about 1 to 40 percent, is composed partly 

of very fine grained apatite ( ?) , ilmenite, troilite, alkali 

feldspar ( ?) , glass, and unidentified minerals (Lunar 

Sample Preliminary Examination Team, 1971). It is 

possible that sample 14310 and similar clasts are 

products of near-surface rocks that were shock melted 

(Dence and others, 1972). 

TABLE 4. - Modal compositions of basalts, in volume pe1·cent 

[Tr., trace] 

Interscrtal 

Plagioclase ........... 60 55 60 58 70 

Pyroxene ..... 30 35 30 19 

Olivine ................. .. 1 

Opaque ..... ........... Tr.Tr. 1 2 Tr. 

Mesostasis ............ 10 10 39 10 10 

Ophitic 

55 40 50 50 

39 58 45 45 

5 1 5 5 

1 1 ........ 

Intergranular 

80 50 

10 50 

2 .. .. 8 .. .. 

Aphyric basalt clasts and microclasts with ophitic 

texture ( c~) are almost as abundant as intersertal 

basalts, and the two types may intergrade. In rock 

14310, intersertal texture tends to grade toward ophitic or subophitic texture as the grain size increases. 

This group of clasts differs from the ophitic parts of 

14310 mainly in having a small percentage of olivine. 

Clast sizes in thin section are as large as 5 mm, but 

the largest C2 clast returned is sample 14053. Average 

grain sizes are somewhat coarser than those of C1 

rocks (table 3), as large as 0.6 mm in rock 14053 

(Melson and others, 1972). These rocks typically have 

lower plagioclase contents ( 40-50 percent) than intersertal basalts (table 3), probably in part due to nonrepresentative sampling of small clasts. Plagioclase 

forms euhedral grains that penetrate larger anhedral 

to subhedral pyroxenes (fig. 8B). Olivine occurs 

sparsely, usually as ragged grains in cores of pyroxenes. Opaque minerals (metallic iron, ilmenite, troilite) 

are not abundant (table 3) . Tridymite and cristobalite 

occur in interstices and vugs of some rocks, and some 

rocks contain 1 percent or less of interstitial material 

(including metallic iron, dendritic ilmenite, fayalite( ?), 

and glass (Lunar Sample Preliminary Examination 

Team, 1971). 
10 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 
THIN-SECTION PETROLOGY 11 

Clasts of basaltic rock with intergranular ( C3 ) and 

variolitic ( C4 ) texture are moderately widespread (fig. 

6) but are not abundant. Modes are given in table 4, 

size data in table 3. 

Clasts of basaltic rock with vitrophyric texture ( C5 ) 

have been found in thin sections of seven rocks (fig. 

6) . These clasts are as large as 4 mm (table 3) and 

either are irregular angular to subangular fragments 

or have nearly perfectly circular cross sections (fig. 

8C). The circular ones are among the features called 

chondrulelike by King, Butler, and Carman (1971, 

1972) and by Fredriksson, Nelen, Noonan, and Kraut 

( 1972). Five subtypes, all containing very dark brown 

glass, were identified on the basis of their mineralogy 

(table 5). 

TABLE 5.- Types of vitrophyres 

Group Crystal phases 

C;;a---··································Plagioclase only. C;;JJ ..................................... Olivine only. 

C;;c ..................................... Plagioclase, olivine. 

C;;d ..................................... Plagioclase, clinopyroxene. 

C5•·····································Plagioclase, olivine, 

clinopyroxene. 

Clasts of graphic to irregular intergrowths of alkali 

feldspar and quartz (C6 ) are widespread but not 

abundant. Irregular quartz grains are intergrown with 

larger (table 3) alkali feldspar grains (fig. 8D). In 

places irregular blades of quartz that are comparable 

in one dimension to the alkali feldspar are intergrown 

with alkali feldspar. 

FIGURE 8.- Photomicrographs of Apollo 14 rocks. A, Photomicrograph of fine-grained cognate inclusion (upper left 

% of photograph) in 14310,10. Boundary with normal 

rock is gradational, and both parts are composed of 

plagioclase laths, pyroxene, a trace of opaque minerals, 

and fine-grained interstitial material. B, Photomicrograph 

of ophitic basalt, 14053,6. Plagioclase laths penetrate zoned 

pigeonitic pyroxenes. Opaque minerals and olivine are 

scarce. C, Photomicrograph of a round clast of vitrophyre 

composed of skeletal olivine prisms and a small amount of 

plagioclase in finely devitrified glass. 14318,8. D, Photomicrograph of a clast that consists of a graphic intergrowth 

of quartz and alkali feldspar. 14318,8. E, Photomicrograph 

of a cumulus clast composed of euhedral cumulus 

plagioclase and orthopyroxene (higher relief than the 

plagioclase) in a groundmass of finer grained postcumulus 

plagioclase, pyroxene, opaque minerals, and glass. 14321,29. 

F, Photomicrograph of a cumulus clast composed of 

euhedral cumulus plagioclase with postcumulus clinopyroxene. 14171,13. G, Photomicrograph of a dark aphanitic ( D4) metaclastic clast composed of porphyroclastic 

plagioclase and a finely recrystallized plagioclase clast 

(Dt) near center, in a dark microcrystalline matrix. 

14063,28. H, Photomicrograph of a light-colored (D2 ) 

metaclastic rock with plagioclase porphyroclasts in a 

moderately coarse grained granoblastic matrix composed 

of plagioclase, orthopyroxene, and opaque minerals. 14042,7. 

Bar scale 0.5 mm long. 

Rocks with cumulus textures ( C7 ) are among the 

most widespread igneous clasts (fig. 6), though they 

are not as abundant as either intersertal or ophitic 

basalts. They are typically subangular to subrounded 

and are as much as 2.0 mm in size (table 3). Seven 

varieties of cumulates are identified on the basis of 

types of cumulus and postcumulus phases (table 6). 

TABLE 6. - ll1 odes and average g1·ain sizes of common cumu- lates 

Cumulus minerals Postcumulus Average cumulus (volume percent) phases grain size (mm) 

Plagioclase ( 45) Orthopyroxene (55) 0.05 

Opaque (trace) 

Clinopyroxene and Plagioclase (58) 0.05-0.07 

olivine (42) Opaque (trace) 

Plagioclase (37) Plagioclase (27) 0.05 

Orthopyroxene ( 13) Pyroxene ( 20) 

Glass (3) 

Plagioclase ( 40) Clinopyroxene (55) 0.07 

Opaque (5) 

Plagioclase ( 79) Clinopyroxene ( 15) 0.13 

+ postcumulus Glass (6) 

overgrowth ( ? ) Opaque (trace) 

Clinopyroxene ( 42) Plagioclase (58) 0.06 

Opaque (trace) 

Plagioclase ( 40) Plagioclase~~~~~~~~~} (with tiny Orthopyroxene .. 0.13 olivine (?) ~i~::.i. -~-~~-~-~-~-~-~---· ( 60) inclusions) 

The textures of these rocks vary considerably (figs. 

BE, F), depending in part on the degree of postcumulus modifications in the shape of cumulus grains. 

Plagioclase is the dominant cumulus phase in all but 

one variety and is the only cumulus phase in three 

(table 5). Other cumulus minerals are clinopyroxene, 

orthopyroxene, and olivine. Postcumulus material includes plagioclase, glass, opaque minerals, clinopyroxene, orthopyroxene, and alkali feldspar. 

Clasts composed of igneous rock with hypautomorphic granular textures (C8 ) are moderately widespread (fig. 6). Most are subangular clasts as much 

as 7.5 mm in diameter (table 3). One is norite composed of about 45 percent plagioclase, 50 percent 

orthopyroxene, 4 percent clinopyroxene, and 1 percent opaque minerals. The other coarser clasts (table 

3) are gabbros and anorthosites. Their coarse grain 

size suggests that small clasts will not yield representative modes. 

METAMORPHIC ROCKS 

Seven types of metamorphic rocks (class D, table 2) 

occur as clasts and microclasts in the Apollo 14 fragmental rocks : two varieties of metaclastic rocks (one 

dark and one light colored), metabasalts, metagabbros, 

and three main types of recrystallized mineral grains. 
12 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

All these metamorphic rocks have some variant of 

hornfels texture, with relicts of angular material that 

suggest a premetamorphic cataclastic texture. 

Metaclastic rocks are the most abundant of all clasts 

in the Apollo 14 fragmental rocks. They are characterized by the presence of relict angular crystal debris 

(porphyroclasts), ranging from a trace to 75 percent 

of the rock or more, in a granoblastic or poikiloblastic 

matrix. Plagioclase dominates as a relict mineral, 

but clinopyroxene, orthopyroxene, olivine, and quartz 

occur. Of the two varieties, the dark-colored clasts 

(D4) are more abundant than the light-colored ones. 

D4 metaclastic rocks are principally recrystallized 

cataclasite and ultracataclasite (Spry, 1969), which 

are dark both in hand specimen and in thin section 

(table 2; fig. 8G). Clast sizes in thin section are as 

large as 8.0 mm. Though there appears to be a gradation in this class from extremely fine grained very dark 

rocks to somewhat coarser lighter gray rocks, some 

breccias (for example, 14306, 14063, 14312, 14171) 

have distinct clasts at both ends of the spectrum, with 

few intermediate individuals. In places, these contrasting types are interbanded, and in others, one type may 

occur as clasts in the other. Even the coarsest grained 

rocks of this type are too fine grained to enable identification of most minerals, but they appear to have a 

higher opaque-mineral content than the light-colored 

metaclastic rocks, and the pyroxenes appear to be 

principally clinopyroxene. Some of these clasts show 

evidence of having been partly fused (buchite), and 

small amounts of glass have, in a few samples, survived recrystallization. In others, the original presence 

of a melt is indicated by occurrence of vesicles and of 

small microlites of olivine or plagioclase along with 

the coarser porphyroclasts. 

A second common variety of recrystallized cataclasites (D2) are light colored in hand specimen and 

in thin section (table 2) . These rocks are generally 

coarser grained than the dark metaclastic rocks, and 

they are characterized by granoblastic or poikiloblastic 

textures. Granoblastic textures (fig. 8H) tend to become granoblastic-polygonal with increasing grain 

size. In rocks with poikiloblastic texture (fig. 9A, B), 

the host mineral (orthopyroxene or clinopyroxene) 

enclosing plagioclase granules ranges in size from 

>0.05 to 0.10 mm. Some of the more coarsely recrystallized clasts also show development of porphyroclastic plagioclase (fig. 9C) and growth of small 

lath-shaped plagioclase grains. Where such rocks lack 

porphyroclasts, they resemble plagioclase cumulates, 

except for their fine grain size. In general, however, 

the former fragmental nature of these rocks is clearly 

evidenced by their angular grains and very poor 

sorting. Plagioclase is clearly the dominant mineral, 

although its proportion is extremely variable. In the 

majority, orthopyroxene is the most abundant mafic 

mineral. Clinopyroxene occurs with the orthopyroxene 

in some rocks and is the only pyroxene in a few; the 

consistently low birefringence of the clinopyroxene 

suggests that it is mainly pigeonite. Opaque minerals 

are a constant accessory, and small amounts of porphyroclastic olivine are common. 

Metabasalts with granoblastic textures (D3 ) are 

moderately widespread but are not abundant (fig. 5). 

Most of these appear to have had intergranular or 

intersertal textures before metamorphism and now 

consist of a granular aggregate of augite, with or 

without olivine, equant opaque minerals, and ragged 

plagioclase that commonly tend to poikiloblastically 

enclose other minerals. The rocks closely resemble 

hornfelsed basalts in the Apollo 11 samples, described 

by James and Jackson (1970), though many are 

coarser grained. Typical modes and grain sizes are 

given in table 4. 

The metagabbros ( D7) are not only rare, but' also 

unusual rocks. A few of them may have been troctolites 

(figs. 9D, E) in which what appear to be cumulus 

olivine grains are distributed among plagioclase grains. 

Both the olivine and the plagioclase have been recrystallized to fine-grained granoblastic aggregates, but the 

original texture of the rock is preserved. An even more 

striking example is illustrated in figure 9A and B, in 

which original euhedral shapes of plagioclase, possibly 

ophitically enclosed by pyroxene, are preserved despite 

coarse recrystallization to a decussate mosaic. 

Virtually monomineralic clasts of plagioclase or 

olivine hornfels are common, and similar ones of 

clinopyroxene and orthopyroxene occur sparsely. The 

clasts typically are ovoid and subround but may be 

blocky and angular. Their size ranges from 0.01 to 

3.0 mm but averages about 0.25 mm. Grain sizes vary 

FIGURE 9.- Photomicrographs of Apollo 14 rocks. A, Photomicrograph of a light-colored (D2 ) metaclastic rock with 

poikiloblastic orthopyroxene enclosing small plagioclase 

grains. 14082,12. B, Same area as 9A. Crossed nicols. Note 

zoning of porphyroclastic plagioclase. C, Photomicrograph 

of a light-colored (D2 ) metaclastic rock with porphyroclastic plagioclase in a coarse-grained matrix composed of 

orthopyroxene poikiloblastically enclosing plagioclase laths, 

crossed nicols. 14063,25. D, Photomicrograph of a "metatroctolite" composed of olivine and plagioclase. Plane polarized light. 14301,13. E, Same as 9D, crossed nicols, showing 

granoblastic recrystallization of both olivine and plagioclase. F, Photomicrograph of a "metagabbro" clast with 

euhedral plagioclase grains enclosed by clinopyroxene. 

Plane polarized light. 14270,9. G, Same view as 9F, crossed 

nicols, showing decussate recrystallization of the plagioclase 

and granoblastic texture of the pyroxene. H, Photomicrograph of clast with areas of a single relict plagioclase 

grain, crossed nicols. 14312,19. Bar scale 0.5 mm long. 
THIN-SECTION PETROLOGY 13 
14 PETROLOGY AND STRATIGRAPHY, FRA MAURO FO]{l\IATION, APOLLO 14 SITE 
THIN-SECTION PETROLOGY 15 

somewhat (range 0.03 to 0.08 mm), with typical grain 

sizes for the plagioclase clasts at the lower end of the 

range and for olivine clasts at the upper end. Plagioclase hornfels (D1) are by far the most abundant of 

the monomineralic hornfels and show the widest 

variety of textures. Most plagioclase clasts consist of 

fine interlocking anhedra that are either elongate blebs 

or irregular in shape. Spherulitic texture in the plagioclase clasts is common and in some is spectacularly 

developed (fig. lOA). A few plagioclase clasts have 

granoblastic-polygonal textures that closely resemble 

those in Apollo 11 rocks described by Wood, Dickey, 

Marvin, and Powell ( 1970a, b), and others have striking decussate textures resembling the feldspar in 

metagabbro clasts. Olivine hornfels (D5 ) typically 

have granoblastic-polygonal textures (fig. lOB) and 

are composed of interlocking grains of undeformed 

olivine. Pyroxene hornfels (DG) are uncommon, and 

those composed of orthopyroxene are especially rare. 

Both have granoblastic-polygonal textures. 

Relicts of the mineral grains that recrystallized to 

hornfels are present in a number of these clasts; no 

polycrystalline relicts of mafic silicates were observed, 

the unrecrystallized material in all samples being relicts of a large single grain (fig. lOG). However, a few 

incompletely recrystallized plagioclase clasts have relicts that suggest a polycrystalline source, and we cannot be sure that we have not counted some previously 

polygranular plagioclase aggregates in this group. It 

is nevertheless clear that the great majority of these 

monomineralic aggregates are recrystallized single 

FIGURE 10.- Photomicrographs of Apollo 14 rocks. A, Photomicrograph of a clast of spherulitically recrystallized feldspar. 14301,16. B, Photomicrograph of olivine hornfels 

microclast with granoblastic-polygonal texture. 14066,5. 

C, Photomicrograph of olivine microclast, showing partial 

recrystallization of single kink-banded olivine grain. 14066,7. 

D, Photomicrograph of partly reacted olivine microclast 

surrounded by a corona of pyroxene and an opaque mineral. 

Note lightened halo in matrix around corona. Small 

"olivine" adjacent to right side of large one is completely 

replaced. 14308,3. E, Photomicrograph of a plagioclase 

porphyroclast in a poikiloblastically recrystallized D:? metaclastic rock. Plagioclase porphyroclast has a narrow sodic 

reaction rim. 14063,8. F, Photomicrograph of red spinel 

microclasts with colorless feldspathic reaction rims. Largest 

spinel grain (lower center) has darkened borders next to 

the corona, while smaller grains are dark throughout. 

14171,13. G, Photomicrograph of quartz microclast, crossed 

nicols, showing quartz core surrounded by an envelope of 

glass that in turn is surrounded by a corona of pyroxene. 

14066,7. H, Photomicrograph of clast of partly fused graphic 

quartz-alkali feldspar intergrowth, crossed nicols. Fusion 

occurs along grain boundaries (wide black bands) in the 

interior of the clast. Quartz at the edge of the clast has 

reacted with the matrix to form a pyroxene corona. 

14305,102. Bar scale 0.5 mm long. 

crystals. It is possible that they were formed from disaggregated coarse-grained metagabbros like those 

illustrated in figure 9 (D-G). Ave'Lallement and 

Carter ( 1972) attributed the conditions of recrystallization to shock processes. However, we have observed 

olivine with a similar texture in an unshocked olivine 

pyroxenite inclusion in basalt from Kilbourne's Hole, 

N. Mex. Also, Wilson ( 1969) described recrystallization of pyroxene in granular aggregates in terrestrial granulites without modification of original grain 

shapes. It seems quite clear that these lunar materials 

are partly to completely recrystallized mineral grains 

and do not represent fragments of lunar anorthosite, 

pyroxenite, or dunite. 

MATRIX MATERIALS 

Examination of surface photographs of boulders of 

breccia ejected from Cone crater ( Hait, 1972) has 

shown the presence of some clasts that are larger than 

many of the returned samples. Since many of the 

clasts in the breccias are themselves fragments of 

breccia, the relative age of the "matrix" of any particular breccia sample is difficult to establish. The 

problem of distinguishing the youngest, or Fra Mauro, 

matrix is discussed in a later section; in the following 

discussion, "matrix materials" refers to the youngest 

binding agents of any particular sample. 

It is apparent in hand sample and thin section that 

the clasts in the Apollo 14 fragmental rocks have a 

seriate distribution and that our division by grain size 

into clasts ( > 1.0 mm) and microclasts (0.1-1.0 mm) 

is arbitrary. Aside from a major increase in proportion of mineral microclasts in all rocks and of glass 

microclasts in those rocks that contain glass, the types 

and relative abundances of microclasts do not differ 

significantly from those of clasts. A comparison of the 

kinds of lithic clasts and lithic microclasts in the same 

rock (fig. 6) show that the proportions of rock types 

are much the same. Indeed, the grain sizes of the most 

abundant lithic clasts are such that they are commonly 

not disaggregated in the 0.1- to 1.0-mm-size fraction. 

One cannot readily account, therefore, for the origin of 

the large percentage of mineral fragments in the 0.1-

1.0-mm size range. (See fig. 6.) A small proportion of 

these fragments were almost certainly derived by 

comminution of porphyroclasts in metaclastic rocks; 

for example, some plagioclase fragments are broken 

across sodic reaction rims that characterize these porphyroclasts. However, in most rocks, the proportion 

of plagioclase fragments is not high enough to suggest 

a porphyroclast source. Moreover, the comparative 

abundance of mineral microclasts is not matched by 

the generally low proportions of porphyroclasts, and 

the typical size of porphyroclasts is not larger than 

the mineral fragments. A more likely source for the 
16 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

mineral fragments is the coarser grained gabbros with 

hypautomorphic granular texture. The mineral proportions in the clasts of gabbro are consistent with 

the mineral fragment distributions, although the relative paucity of gabbroic rocks among the lithic clasts 

is difficult to explain. 

Rocks containing much clastic glass in the >0.1-

mm-size fraction (F11 F 2 ) also appear to be bound by 

glass that, if fragmental, is too small to resolve microscopically in thin sections.3 Rocks lacking glass clasts 

( F 3, F 4 ) are bound by very finely crystalline apparently annealed material that is generally finer grained 

than most clasts of metaclastic rock. In some of these 

rocks, spherical and broken spherical fragments that 

presumably were formerly glass are now composed of 

fine crystalline material. Warner (1971, 1972) has 

subdivided the Apollo 14 breccias, using the relative 

abundance of glass clasts and of glass in the matrices 

as his principal criteria. He thus divided the rocks 

into six categories (from glassy "detrital" breccias to 

glass-free "annealed" breccias), which span our F1-F4 

types. 

MATRIX-CLAST REACTIONS 

In a number of fragmental rocks, partial to complete reequilibration reactions have taken place between youngest matrices and some clasts and have 

clearly occurred subsequent to the formation of the 

breccia. In other rocks, similar reactions have been 

observed within the clasts but not within the youngest 

matrix, which suggests that these reactions are preconsolidation features. 

Postconsolidation mineral Teactions.-Mineral clasts 

and microclasts of olivine, plagioclase, spinel, and 

quartz commonly have reacted with the matrix containing them. Reaction products of olivine and matrix 

are orthopyroxene and ilmenite (fig. lOD). The apparent proportions of reaction products vary widely. 

The matrix appears in places to have been lightened 

in a faint halo around reacted grains (fig. lOD) to 

form a rim half as wide as the original diameter of 

the olivine. Irregular clasts of plagioclase commonly 

are surrounded by a narrow reaction rim of more 

sodic plagioclase (fig.lOE) ; in one example, reversed 

zoning was observed. Pale-pink to orange- or redbrown clasts of spinel ( ?) typically have reacted with 

the matrix to produce a compositional zoning (darkening) on the spinel and a corona of colorless, often 

radially fibrous material (feldspar) (Roedder and 

Weiblen, 1972; fig.lOF). Quartz has reacted with the 

matrix to form a corona of pyroxene; the pyroxene 

rim is typically separated from the quartz by a thin 

3This type of glass differs conspicuously from "splash" glass that also 

cements some breccias, the largest of which is 14306. The "splash" glass 

contains very irregularly distributed fragmental material and is highly 

vesicular. 

band of color]ess glass (fig. lOG). In addition, both 

orthopyroxene and clinopyroxene appear to be compositionally zoned by reaction. Opaque minerals have 

also reacted, but these have not been closely examined. 

The degree of reaction between minerals and matrix 

of the breccia containing them is very erratic, and 

grains showing well-developed reaction may occur 

side by side with those showing no reaction. However, 

there does appear to be a general sequence of reaction 

and also a correspondence between degree of recrystallization of the matrix (\Varner, 1971, 1972) and 

degree of reaction. The earliest sign of reaction is the 

conversion of olivine to orthopyroxene + ilmenite. 

Interchange of components between the olivine and 

matrix is shown by light halos around such reaction 

rims. This reaction is observed in rocks in which no 

other minerals are visibly affected. The next reaction 

that occurs at a stage at which the pyroxene-ilmenite 

rims on olivine are still poorly developed is peripheral 

darkening of translucent spinel grains. Compositional 

zoning of plagioclase is commonly observed in rocks 

in which some olivine grains are completely reacted, 

and spinel grains may exhibit coronas of radially 

fibrous plagioclase. The olivine reaction is at best 

poorly developed in the glassy rocks; hence, the other, 

more advanced reactions probably occurred concomitantly with crystallization or recrystallization of the 

matrix of those rocks that now contain little or no 

glass. Careful examination of the phases involved may 

allow definition of facies of metamorphism. However, 

it should be emphasized that disequilibrium is the rule 

in these rocks and that meaningful temperature-pressure conditions of metamorphism will be most difficult 

to ascertain. 

Table 7 summarizes the observed reaction phenomena. The two F 2 rocks contain fairly abundant glass 

clasts and microclasts. The remainder of the rocks 

exhibiting this reaction are classified as F 4 ; only one 

(14306) contains a minor amount of glass. All the 

rocks in which we have observed the reacted plagioclase and spinel are type F 4 and glass free. 

Preconsolidation mineral reactions.-The same evidence of disequilibrium is found between porphyroclasts and their matrix in individual clasts as between 

mineral fragments and the youngest matrix in certain 

fragmental rocks: olivine has reacted to form orthoTABLE 7.- Distribution of 'mineral reactions 

Sample Rock No. type 

14301 F., 

14307 F~ 

14304 F~ 14306 F4 

14308-14311 F 4 

14319 F4 

14321 F4 

Mineral reaction 

Olivine. 

Do. 

Olivine, spinel, plagioclase. 

Do. 

Do. 

Do. 

Do. 
THIN-SECTION PETROLOGY 17 

pyroxene and ilmenite, plagioclase has developed a 

sodic rim, and spinel has reacted to form a felsic ( ?) 

corona and complementary compositional zoning within 

the spinel. We have, in fact, noted these reactions in 

clasts in all of the rocks in which matrix-mineral clast 

reactions were noted above. In addition, we have 

observed reaction rims in clasts in several glassy fragmental rocks in which no young matrix reactions were 

seen. These rocks include members classified as types 

F1, F~. FH, and F4. We can only conclude that the 

reequilibration that affected these clasts took place 

prior to their incorporation into the Apollo 14 fragmental rocks. 

PARTIAL FUSION 

In several fragmental rocks (14270, 14303, 14305, 

14306, 14315, 14318), quartz and quartz-alkali feldRpar intergrowths were partly melted. Isolated quartz 

grain::; and those at the edges of quartz-feldspar clasts 

have colorless glass rinds that have reacted with the 

matrix to form characteristic pyroxene coronas. In 

the interiors of quartz-alkali feldspar clasts, partial 

fusion began along the grain boundaries of quartz and 

feldspar (fig. 10H). As in the mineral reactions 

described above, the effects of partial fusion are quite 

erratic, with extensively fused clasts occurring side 

by side with similar clasts showing no fusion. Partly 

melted clasts occur both as fragments isolated in the 

matrix of the rock and as clasts within larger fragmental clasts. In general, evidence concerning the time 

of melting, before or during formation of the breccia, 

is ambiguous. In one sample, however, melting clearly 

occurred after consolidation of the breccia: a melted 

part of a fragment of the metaclastic rock has intruded adjacent matrix (fig. llA). Similarly, reaction between the matrix and partly melted quartz at 

the edges of some clasts also indicates fusion after 

formation of the breccia. 

In some rocks, the glass resulting from partial 

fusion of quartz-feldspar intergrowths is the only 

glass remaining in the rock. (See also Dence and 

others, 1972.) In other rocks, material composed of 

fine-grained alkali-feldspar (?)-bladed quartz intergrowths suggests that melted clasts have devitrified. 

Devitrified quartz-feldspathic material is remarkably 

similar, both texturally and in mode of occurrence as 

both angular clasts and irregularly "intrusive" bodies, 

to Apollo 12 rock 12013 (Drake and others, 1970; 

James, 1971). 

DEFORMATION OF MINERAL AND LITHIC CLASTS 

All the varieties of mineral and lithic debris in the 

fragmental rocks described above show various degrees of deformation. Most plagioclase microclasts are 

mildly deformed by fracturing, and many show weak 

lattice distortion by undulose extinction; some are 

more severely deformed, as evidenced by mosaic texture and conversion to maskelynite. Many pyroxene 

microclasts are undeformed or weakly fractured, but 

some have well-developed shock-formed planar structllres. Olivine microclasts are more commonly deformed, usually by development of broad kink bands. 

The lithic fragments responded in the same ways 

to deformation. Some of them have textures ranging 

from those of weakly deformed cataclasites to severely 

shocked rocks in which maskelynite is well developed. 

Cataclastic rocks, composed of partly crushed, incompletely recrystallized material, are especially conspicuous among the small fraction of coarse-grained 

gabbroic clasts (fig. llB). Apparently plagioclase is 

more susceptible to recrystallization in these rocks, 

and the mafic silicates remain as crushed aggregates. 

Isolated mineral clasts, especially of olivine and 

pyroxene, closely resembling the same minerals in 

these cataclasites, occur sparsely in the fragmental 

rocks. Marginal crush zones and partial mixing with 

debris of the host rock matrix (fig. 11C) indicate 

that some cataclasis occurred after isolation of the 

clast from its source rock. This texture is remarkably similar to marginal crush zones on clasts in the 

impact breccias of the Vredefort ring, South Africa 

(Wilshire, 1971). 

Gradations from crushed rock that still retains its 

original textural identity to highly disaggregated 

debris in which fragments of neighboring minerals 

have been partly mixed are observed. Cataclastic deformation of an olivine-bearing rock of intermediate 

composition may have been the source of a small piece 

of soil breccia interpreted by Taylor and Marvin 

(1971) as fragmented dunite that was invaded by 

noritic matrix material. 

Some gabbroic rocks (fig. 11D) are laced by irregular crush zones showing varying degrees of recrystallization, and some olivine clasts show moderate to 

extensive crushing. Most anorthosite clasts that are 

moderately crushed were polycrystalline aggregates 

whose original textures appear to have been metamorphic. Some partly crushed gabbros have igneous 

textures, others are toc1 small to determine the original 

texture. Finer grained light-colored cataclastic rocks 

may represent cataclastically deformed cumulates or 

D2 metaclastic rocks (table 4), and dark ones may 

have been derived from both basaltic rocks and D4 

metaclastic rocks (table 4). Severely shocked rocks in 

which maskelynite is well developed include intersertal 

basalts, D2 metaclastic rocks, gabbros, and plagioclase 

cumulates. 

COMPOUND CLASTS 

Virtually every rock examined contains some compound clasts (fig. llE-G), and in many, such clasts 
18 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 
CLASSIFICATION OF THE ROCKS 19 

are abundant. Many of these are clearly fragments of 

breccias within .which clast and matrix are readily 

identified. Others consist of two or more lithologies 

without a clear host-clast relation; usually, however, 

this can be ascertained by examination of several 

sections. In table 8 the common compound clasts are 

listed with the host lithology and clasts identified. The 

first column of table 8 gives the sample number and 

the main types of simple, noncomposite clasts observed. 

(See fig. 6 for the range and proportion of clast types 

in the entire sample.) For the most part, host-clast 

lithologies are present as simple clasts in the sample. 

It is significant that only one of the compound clasts 

examined has an igneous host, the remainder being 

either light or dark metaclastic rocks. There is much 

greater variety among the included clasts than within 

their hosts; these clasts include not only an abundance 

of metamorphic rocks, but also cumulates, graphic 

quartz-alkali feldspar intergrowths, and intersertal, 

ophitic, and intergranular basalts. In contrast to simple clast populations, intergranular basalts are more 

abundant than intersertal and ophitic types. More 

rarely, a third generation of breccia is evidenced by 

clasts enclosed in second-stage clasts (table 8, column 

3), and in one example (14308), a probable fourth 

generation was recognized (table 8, column 4). Four 

FIGURE 11.- Photomicrographs of Apollo 14 rocks. A, Photomicrograph of a completely melted quartz-alkali feldspar ( ?) 

clast in a dark metaclastic (D4 ) clast. The glass was 

squeezed out of the clast and intruded into the adjacent 

matrix. 14306,65. B, Photomicrograph of cataclastically 

crushed "troctolite." Close view of crushed but not sheared 

olivine and plagioclase aggregate. 14083,8. C, Photomicrograph of crushed zone along edge of anorthosite clast. Top 

of photograph is normal dark matrix of the host rock; 

below that is a partly mixed zone (now recrystallized), 

followed downward in the photograph by unmixed crushed 

anorthosite, and at bottom by relict anorthosite, crossed 

nicols. 14306,3. D, Photomicrograph of gabbro clast laced 

by thin crush zones now partly recrystallized, crossed nicols. 

14321,21. E, Photomicrograph of compound clasts. Clast of 

plagioclase hornfels with decussate texture in a finer grained 

D2 metaclastic clast. 14306,60. Crossed polarized light. F, 

Photomicrograph of compound clast in coarse light-colored 

matrix (lower left corner of photograph). Clast is composed 

of several dark aphanitic fragments of metaclastic rock 

( D4) in a fine-grained slightly lighter matrix. The largest 

clast (right side) has light-colored metaclastic (D2) clasts 

within it. 14306,54. G, Photomicrograph of compound clast. 

Dark aphanitic (D4) clast (left half of photograph) encloses two clasts of light metaclastic rock ( D2) , the top one 

of which contains a large kink-banded olivine porphyroclast. 14306,4. H, Photomicrograph showing "pellet" texture 

characteristic of F2 rocks. Round particles in field of view 

are metaclastic rocks, but well-rounded variolites, vitrophyres, and intersertal basalt fragments also are present in 

the rock. 14318,44. Bar scale 0.5 mm long. 

TABLE 8.- Clasts and matrix types in compound clasts 

Sample No. ; main types Host clast Clasts in 1 Clasts in 2 Clasts in 3 of simple clasts 1 2 3 4 

14042-Al, D2 ............. Glass D4, A1 

14047-Ab A 2, D2······· Glass D2, At 

14049-Ab D2·············· Glass n., 

14063-D4·-··················· D4 n;, D2 

14066-D4····················· D2 D:;, G;, D2, 

Dt 

D4 D:.! 

14301-D2 .................... D::! c3, c7, D1, 

D::!, D:o 

D4 c1, c7, D1 

14303-D4 ..................... D4 CG, D:.! 

14304-D4 .................... D4 D1, D:.!, D:o 

14305-D4 ..................... D4 D1, D-· 

14306-D-l·-·················· D4 c1, D1-, D4 D:.!, D4 

14307-D2 ..................... D·· D:o, D1 D~ C:h D3 

D3 D1, D4 

14308-D4 ..................... D4, D4 D-· D4 D;; 

14312-D4 ..................... D4 D~ 14313-Al, D4---··········· C;; D-· 

D4 D~ n., D4 

14314-D4 .................... D~ D2, D.h D;;, 

c7 

14315-D2 , D4-·-··········· D4 A::!. C:.!, D4 

generations of breccias were also observed in sample 

14321 by Duncan and others ( 1972). 

In one sample (14306), the clasts within host D4 

clasts were counted; although the proportions of these 

clasts are measurably different from those of the first 

generation of breccia, the essential properties of the 

F4 class of rock 14306 are retained (compare positions 

for I3c and 14306 in fig. 12A and B). It is interesting 

and significant that older generations of clasts are of 

metaclastic rocks, clearly showing a history of multiple brecciation and metamorphism. 

CLASSIFICATION OF THE ROCKS 

Our classification of the Apollo 14 hand specimens 

is based primarily on coherence and on proportion of 

light and dark clasts and secondarily on the abundance 

of clasts and the proportion of glass (Jackson and 

Wilshire, 1972). The abundance of clasts (again arbitrarily limiting this term to fragments greater than 

1 mm in diameter) is difficult to evaluate in thin 

sections, both because of the small sample size represented even by many sections and because of sectioning effects. Nevertheless, insofar as we could judge, 

the observations from hand specimens were supported 

by those from thin sections. We had difficulty in finding 1.0-mm fragments in rocks that we had classified 

as F 1 and F 3 , but no difficulty in making statistically 

meaningful counts of clasts in types F2 and F4. (See 

fig. 6.) Considering the relative abundance of the 

different clast types (fig. 6), it is clear that the light 

and dark clasts serving as a basis for the hand-specimen classification are predominantly light and dark 

metaclastic rocks. In the following section, other less 

abundant lithic clast types are added to the light or 
20 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

04 ':' l71, 308 

I 305 

Dark metaclastic rocks 

3. o6~ F4 

306 

303' 314- -321 

ALL A-01+2+3 -04 

>1mm 

/ 

\·31~ 

•315 

A Light clasts 0 1+2 +3 

ALL C- 0 1 +2 +3 - 04 -063 

I 304· -~82 OK 

.1-1 mm 

I 

/:: I 

/~ 

k 

/ 

C Igneous 

,-~;-

\1 

;k- •314 \ 

/' 308 \ ,-t ( -321 . ·13c F4 

I , -~ ·303 \ 

/~ -~-------- "305 315':" 

~~ 066" 

-----~ \~ F3,~ \ 

1 \ ~~·9 /.318 3~~.\.) \ \:~. ·. F 1 "~--:30/\o 2 

\ \ \ \ . 

v " 0§2- LT\v \04'! \/ 'y 

c 

Light clasts 01+ 2+3 

FIGURE 12. - Triangular plots of clasts and microclasts of 

glass, igneous, and metamorphic rocks. A, Triangular plot 

of glass (A), light-colored metamorphic rocks (D1-D3), and 

dark-colored metamorphic rocks (D4), showing fields of 

rock groups F1, F~, and F 4 • B, Triangular plot of microclasts, as in part A above. C, Triangular plot of clasts of 

dark metaclastic rock proportions where appropriate, 

but the same results would be obtained if they were 

ignored. 

Coherence was impossible to measure in thin section, but the percentage of glass clasts was not. Figure 

12A shows a triangular plot comparing the proportion 

of glass clasts to those of light-colored rocks (the total 

of Db n~, and D3 types) and dark-colored rocks (D4) 

in thin sections available to us. A clear separation is 

ALL A- 01+2+3- 04 

.1-1 mm 

/ 

/I: 

/ 

A Glass 

308 

304' ...... 314 

082-0K'~I3c F:.11 063' 303 / 6t / 

305 

F3 

B 

D 

·J07 

-301 \ 

Light clasts 01+2 +3 

C + 0 Igneous and metamorphic rocks 

321 

306· 308 /F: .11 

314 ' :61-

304 0;2-0K 

13c 

F3______._\ 303 

, 82 -LT 

063" 66 

305 

\ 

Mineral clasts 8 

igneous rocks (C) , dark-colored metamorphic rocks ( D4), 

and light-colored metamorphic rocks (D1-D3), showing 

fields of rock groups F1, F~, F3, and F4. D, Triangular plot 

of clasts of igneous and metamorphic rocks ( C and D) , 

glass (A), and mineral grains (B), showing fields of rock 

groups F1, F2, F3, and F 4· 

found between F 1, F 2, and F 4 types in terms of lightand dark-clast ratios. It is also apparent that the F 2 

rocks are more apt to contain glass than the F4 types. 

Much better statistical reliability can be obtained from 

the microclast data. The same plot for fragments in 

the size range 0.1 to 1.0 mm is given in figure 12B. 

The same clear separation of light and dark clasts of 

F ~ and F 4 rocks is apparent. Furthermore, the proportion of D4 clasts in F1 rocks is, on the average, even 
ROCK DISTRIBUTION 21 

less than that of F 2, although some overlap is seen. 

The proportion of glass microclasts is also significantly 

different between groups- only two rocks classified 

as F 4 types contain glass microclasts, whereas all of 

the F 2 types contain significant amounts, and F 1 rocks 

contain more than 50 percent glass in this size range. 

Only two F 3 rocks were available for counting, and 

sample 14082 proved to be layered; the counts suggest 

that its darker layered component is like that of F 4 

material, whereas its lighter component is unlike any 

of the other rocks. Sample 14063 has the same clast 

distributions as the F 4 group, but differs in having a 

white friable matrix. 

A plot of microclasts of igneous rocks (all of group 

C in table 3) against dark (D4 ) and light (Dh D2, 

and D3 ) metamorphic rocks is given in figure 12C. 

The light and dark metamorphic rock separation is 

again apparent between F4 and F 1-F2 groups. The 

proportion of igneous rocks in the F 1 rocks is clearly 

very low, and there is an apparent tendency for F 2 

rocks to contain fewer igneous rock clasts than F 4 

rocks, although the areas overlap somewhat. 

Finally, all lithic microclasts were plotted against 

glass and mineral fragments in figure 12D. While the 

clear separation of types F b F 2, and F 3 is largely due 

to glass content, it is apparent that type F 2 contains 

considerably higher proportions of lithic than mineral 

fragments in this size range. In contrast, the reverse 

is generally true for the other groups. F 4 rocks tend 

to have higher pyroxene-plagioclase ratios than F 1 and 

Fz rocks. 

With these features in mind, we can summarize the 

megascopic and microscopic characteristics of the four 

classification groups. 

Rocks in the F 1 category are friable and contain 

few clasts larger than 1.0 mm. Where such clasts 

occur, they are very dominantly light colored. In the 

microclast size range, fragments consist of more than 

40 percent glass with respect to mineral and lithic 

fragments. Mineral fragments are composed of 50-60 

percent plagioclase, 35-50 percent pyroxene, and less 

than 10 percent olivine. Lithic fragments are strongly 

dominated by light-colored metamorphic rocks; igneous rocks make up less than 5 percent of the total 

lithic microclast population. Reactions between clasts 

or microclasts and matrix have not been observed, 

and multiple clasts are rare. 

Rocks in the F 2 category are moderately coherent 

to coherent, contain abundant clasts, and have a striking pelletlike texture (fig. 11H). The clasts are dominantly light colored, but not so exclusively as those of 

F 1 rocks. In both clast and microclast size ranges, the 

fragments consist of more than 50 percent lithic fragments with respect to mineral and glass fragments. 

Glass fragments are everywhere present, however. 

Mineral fragments are principally plagioclase (60-90 

percent), but olivine and pyroxene occur in a wide 

range of proportions (fig. 6). Lithic fragments are 

dominated by light-colored metamorphic rocks but 

contain 5-30 percent igneous rock fragments. Reactions between clasts or microclasts and matrix are 

present in at least two samples, but, in general, they 

are poorly developed or absent. 

Only two rocks in the F 3 category were sectioned, 

and both have friable white crystalline matrices. One 

of these exhibited rather unusual banding. The dark 

bands exhibit F 4 properties in general (figs. 12B-D) , 

but the rock is more friable. The light bands contain 

no D4-type clasts and hence are unlike any of the other 

groups. The second rock resembles the dark bands in 

the first. 

Rocks in the F 4 category are the most abundant in 

the collection. They are moderately coherent to tough 

and contain abundant clasts that are generally more 

angular than those in F2 rocks. The clasts are dominantly dark colored, to the extent that there is no 

overlap in this respect with F 1 and F2 rocks. In both 

the clast and microclast size ranges, glass is very 

scarce (figs. 12..4., B) ; it has been observed only in 

two rocks in this category and then in minor amounts. 

Mineral fragments are relatively abundant with respect to lithic fragments and have approximately the 

same proportions as do those of F2 rocks (fig. 7). 

Lithic fragments are dominantly dark metaclastic 

rocks, which make up 50 percent or more of the lithic 

clasts (fig. 12C). Igneous rocks show a wide range 

( 4-20 percent) of relative lithic clast abundance. 

Reactions between clasts or microclasts and matrix 

are common and occur in at least five of the rocks we 

examined in thin section. 

We emphasize that this classification is descriptive. 

Without intending to imply a genetic connotation, we 

note that the F 1 group of fragmental rocks corresponds to the "porous, unshocked microbreccias," and 

the F 3 and F 4 groups to the "thermally metamorphosed microbreccias" of Chao, Boreman, and Desborough (1971). 

ROCK DISTRIBUTION 

Figure 13 shows the field distribution of F1-F4 

rocks (locations are from Sutton and others, 1971). 

Homogeneous crystalline rocks, believed to be clasts 

broken free from F 2 and F 4 fragmental rocks, are not 

shown on the map. It is at once apparent that the 

sample abundance is heavily weighted toward sites 

close to the lunar module. This would be even more 

conspicuous if samples smaller than 50 g were deleted. 

However, there is a regular pattern in the rock-type 

distribution: 
22 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

~:~:hensiv~ EXPLANATION / .~. -·, Cl 

250A H I Cc4 -' '\ 06Je 

251 A J03 e A Fl I / CONE ., Oo4e • F2 I I 

H~; ~n: .F3.4 \, C?/~~~ }~f! 266. 3156 ~; . / 

267A 3166 A 268A 3176 Contingency!!____ 

1

VJ_J ·- • ~~~: ;~:: ~p1e ~~~: _ryj ~ mL'\ ~· ·~ )~~~-Y ' ff!~· ' ' ' ' -/I G 1 .§.JL I y__ 311. 2786 "" _ ~49. 1 r ·. i,...-- 279~._.7 3016 (_1 ---~ 

2806 LM ~. 3p• \ L 2816 FSR Bulk/ ( ~-~•\ - --.2.556 

282 A 302 • Sam le . . J L !:...__ 05hA ~ 

2856 305·~ \...( ") 075e 06he 05'A \ 

286 6 427 6 TRIPLET 076. 05~ A \ 

430A ('\ 0806 0596 I 43 26 -"45e\_ • 306e Is 0606 

lfr 

43764496 ./ 3076 0616 \ 

43864526 100 ,0 ObZA \~OOMETERS 442 6 453 6 I I ' > - ' 

FIGURE 13. - Distribution of fragmental rock types at the 

Apollo 14 landing site. 

1. All F 1 types were collected from the smooth terrain (fig. 2) outside the continuous ejecta blanket and blocky rays of Cone crater. 

2. The great majority of F:! rocks were collected from 

sites far removed from Cone crater (fig. 13), 

and some were almost certainly collected from 

the discontinuous outer parts of the Cone crater 

ejecta (Swann and Field Geology Team, 1971). 

F4 type rocks also make up a sizable proportion 

of rocks collected from the outer part of Cone 

crater ejecta (fig. 13). 

3. With the single exception of rock 14051, which 

was thoroughly dust covered when examined 

and may well be incorrectly classified, the samples collected from near the rim of Cone crater 

are F3 and F4 types. (See also Quaide, 1972.) 

That dark-clast-rich breccias are indeed the 

dominant variety of rock near Cone crater is 

further supported by the astronauts' descriptions and by the surface photographs of boulders on the flanks of Cone crater (Swann and 

Field Geology Team, 1971; Hait, 1972). 

In terms of the general sequence of deposits in 

ejecta blankets (Shoemaker, 1960), the material collected from closest to the crater is presumed to represent the lowest units reached during crater excavation. 

At Cone crater, that material is fragmental rock with 

dominantly dark clasts (F3 and F4). Material collected 

from farther out on the ejecta blanket (F:! and F 4) is 

presumed to represent material from higher levels in 

the precrater section. Whether the mixture of F :l and 

F 4 types in ejecta at the outer, discontinuous part of 

the Cone crater rays (fig. 13) is due to a thin layer 

of F:! or to complex intermingling of rocks by ejection 

through precrater fractures (Gault and others, 1968) 

cannot be ascertained. 

Our interpretation, therefore, is that the lithologic 

units described above are stratified in the ridgelike 

terrain excavated by Cone crater. The surface of the 

stratigraphic pile away from the young ejecta blanket 

of Cone crater consists of soils and weakly lithified soil 

breccias ( F 1 ) • Light-clast-dominant coherent but glassy 

fragmental rocks ( F J form the upper strata and most 

likely crop out in the upper walls of Cone crater. 

A still deeper unit of dark-clast-dominant coherent 

largely crystalline fragmental rocks ( F 4) was peneh·ated by the Cone impact, and these rocks are concentrated near the rim. The unique "white rocks" 

(Fa) form layers in dark-clast-dominant fragmental 

rocks close to the rim of Cone crater and are presumed to represent the lowest parts of the section 

excavated by Cone crater (Sutton and others, 1972; 

Hait, 1972). 

FRA MAURO FORMATION 

Whether the stratigraphic units described in the 

preceding section represent unmodified Fra Mauro 

Formation, reworked or partly reworked Fra Mauro 

Formation, or more than one formation remains an 

open question. The pre-mission map of the Cone crater 

area (Eggleton and Offield, 1970) shows craters of 

Eratosthenian age as much as half a kilometer in 

diameter and a crater of Imbrian age approximately 

1 km in diameter located in the immediate vicinity of 

the landing area. Shoemaker ( 1972) further contends 

that the Fra Mauro surface was in a steady state for 

craters as much as 1 km in diameter; if so, this suggests considerable reworking of the upper parts of the 

original Fra Mauro deposits. In the immediate vicinity 

of the landing site, known craters half a kilometer in 

diameter may be expected to have ejected materials 

over the future Cone crater site to depths of perhaps 

5-15 m (H. J. Moore, oral commun., 1972). This is 

considerably less than the section ultimately sampled 

by the Cone event. If unrecognized larger impacts did 

indeed affect the Fra Mauro surface in the vicinity 

sampled, it is apparent that they did not modify the 

radial ridge pattern typical of the Fra Mauro surface. 

Hence, the bulk of the material ejected from Cone 

crater probably represents strata deposited before the 

oldest craters in the immediate area were formed. 

The uppermost units (F1-F2) at the Apollo 14landing site are lithologically distinct from underlying 

units and cannot be the result of reworking of lower 

units, despite suggestions to the contrary (Quaide, 

1972; Dence and others, 1972). Hence, they must 

represent either the uppermost surviving units of the 

Fra Mauro Formation or younger, post-Fra Mauro 

rocks. The only tangible evidence we have bearing on 

this question is apparent gradational thermal behavior 

between F!.! and F 4 rocks : metamorphic reactions be-
CONCLUSIONS 23 

tween mineral clasts and matrix are much better developed in F 4 rocks, but olivine has reacted locally with 

the glassy matrix of F ~ breccias. This suggests that 

F:!, Fs, and F4 breccias represent a single cooling unit 

of the original Fra Mauro Formation. 

The viability of our conclusions is dependent on the 

correct recognition of the Fra Mauro matrix proper. 

The presence of breccia clasts in boulders ejected from 

Cone crater that are bigger than many of the returned 

samples does not allow an a priori identification of 

the youngest matrix in any particular sample as Fra 

Mauro. However, the packing density of identifiable 

large clasts is quite low (Hait, 1972), and the probability of sampling the youngest breccia matrix in the 

boulders appears to be high. If the boulders around 

Cone crater are themselves clasts in the Fra 1\'lauro 

matrix, the minimum clast size would have to be larger 

than several meters. "Turtle Rock" (Sutton and 

others, 1971), a 2-m-wide boulder in north boulder 

field, appears to have the same clast population as the 

two san1ples (14321, 14319) taken from the top of the 

boulder. Still larger boulders photographed near Cone 

crater show no signs of huge clast boundaries within 

them, and we find it difficult to believe that every 

block in the field is indeed a clast. Lacking tangible 

evidence to the contrary, we therefore presume that 

the youngest matrices of most breccia samples are the 

Fra :Mauro proper and not matrices of older breccias. 

If we accept the F :_!, F 3 , and F 4 rocks as samples of 

the Fra Mauro Formation and the idea that these 

rocks represent a single cooling unit, then local temperatures on the order of 1,0oooc are required. (See 

also Quaide, 1972; Dence and others, 1972.) Terrestrial exan1ples suggest that temperatures of this magnitude are restricted to areas relatively closer to the 

locus of impact. In the Ries basin (Germany), the 

best-known large terrestrial impact crater that retains 

its ejecta deposits, the high-temperature ejecta (suevite) extends out only about half a crater diameter 

(Pohl and Angenheister, 1969; Dennis, 1971), whereas 

lower temperature breccia deposits (Bunte Breccia) 

underlie the suevite and extend nearly a crater diameter from the crater rim (Dennis, 1971). However, 

these deposits have been subjected to lengthy erosion, 

and the suevite, being in the most easily eroded position, may originally have covered a much larger area. 

The view that the Apollo 14 high-temperature rocks 

are derived from earlier basin-forming events rather 

than from the Imbrium impact (Dence and others, 

1972) does not solve the problem because the source 

area of the Fra Mauro rocks was just as distant from 

earlier major basins, such as Serenitatis or the south 

Imbrium basin (Wilhelms and McCauley, 1971), as 

the Apollo 14 site is from the Imbrium basin. We must 

conclude, therefore, that the magnitude of major lunar 

basin-forming events is such that small terrestrial 

craters do not provide adequate models for temperature distribution in the ejecta deposits. 

CONCLUSIONS 

The site descriptions at the Apollo 14 landing area 

and the nature of the rocks returned by the crew 

strongly support Gilbert's (1893) conclusion that the 

area is covered by ejecta from the Imbrium basin. We 

can apply petrologic observations to a more detailed 

interpretation of the nature and stratigraphy of the 

Fra Mauro Formation by attempting to reconstruct an 

inverted stratigraphic section in the Cone crater 

ejecta. And, on the basis of the clasts in what we 

believe to be Fra Mauro rocks, we can say something 

about the terrane that existed in the Imbrium area 

prior to the enormous impact that produced that basin. 

FRA MAURO FORMATION 

The distribution of rocks collected in the Apollo 14 

landing area suggests that the Fra Mauro Formation 

is stratified. The deepest unit sampled is composed of 

fragmental rocks rich in dark clasts with interlayered 

white fragmental rocks (F4 and F3 ), the next overlying layer is composed of well-indurated fragmental 

rocks ( F ~) rich in light-colored clasts, and the uppermost unit is unconsolidated to weakly lithified (F1 ) 

regolith. 

F 1 type fragmental rocks, characterized by an abundance of glass, weak lithification, and scarcity of clasts 

bigger than 1 mm, were collected from areas not covered by Cone crater ejecta, and in most respects they 

closely resemble the unconsolidated soils of the area 

(Carr and Meyer, 1972; Quaide, 1972). They appear 

to represent poorly lithified regolith that formed either 

by disaggregation and weak re-lithification of F 2 material or from an originally unconsolidated layer of 

fragmental material overlying the F 2 material. Comparison of the clast populations of F 1 and F 2 shows 

that F 1 has more clastic glass, much more pyroxene in 

the microclast size range, and fewer clasts of igneous 

rock than F 2• It is possible that all of these are effects 

of "gardening" of F2 material by small impacts, which 

would tend to produce glass and break down the coarser 

grained clasts more rapidly than the fine-grained clasts. 

However, it remains possible that the regolith and F1 

rocks are derived from a surficial layer overlying F2 

material that was originally of a different composition. 

In our opinion, F 2 rocks represent the upper, consolidated part of the Fra Mauro Formation and are 

probably exposed in the upper walls of Cone crater. 

Glass-filled fractures cross clasts and matrices alike in 

both F 2 and F 4 rocks and are presumably a consequence of the Cone impact, indicating that both rock 
24 PETROLOGY AND STRATIGRAPHY, FRA MAURO FORMATION, APOLLO 14 SITE 

types were consolidated at the time of that event. The 

F2 rocks contain some clastic glass, some of which was 

soft during consolidation of the rocks, and are partly 

bound by glass. Moreover, a few of these rocks show 

the earliest signs of postconsolidation metamorphic 

reaction between mineral clasts and the matrix. The 

simplest explanation of these features is that part of 

the ejecta was hot when deposited and that insulation 

and compaction by upper units allowed induration and 

metamorphism of lower units. The preservation of 

glass and very limited metamorphic reaction suggest 

that all these rocks were near the original top of the 

Fra Mauro ejecta blanket. 

Comparison of the clast populations of F 2 and F 4 

rocks, as well as their general textures, shows that 

these are distinctive rocks and lack intermediate types; 

this is especially evident in the relative abundance of 

light- and dark-colored metaclastic rocks. Hence, we 

infer that the contact between the F 2 and F 4 units in 

the Fra Mauro Formation is sharp. However, since 

neither glass nor metamorphic reactions are unique to 

F2 or F4, it seems likely that the thermal metamorphic 

effects are gradational across the contact. In this respect, the deposits are analogous to cooling units of 

welded tuff deposits. 

F s and F 4 rocks represent the lower consolidated 

part of the Fra Mauro Formation sampled. These rocks 

are largely crystalline, and the original glass clasts 

and glassy matrix material have largely been annealed 

and devitrified. Postconsolidation metamorphic reactions are likewise considerably better developed than 

in F 2 rocks. This feature and the distribution of rocks 

around Cone Crater suggest a deeper source for F 4 

rocks in which the thermal blanketing effect of overlying material allowed slower cooling and partial reequilibration of an assortment of material thrown 

together by impact. Local temperatures were high 

enough (about 1,000°C) to reset partially or completely certain radiogenic systems used to date the 

Apollo 14 rocks (Silver, 1972; Papanastassiou and 

Wasserburg, 1971; Turner and others, 1971; Compston and others, 1971), but the very erratic distribution of metamorphic reactions and partial fusion 

effects indicates uneven heating of debris in the 

blanket. 

PRE-IMBRIUM TERRANE 

The stratigraphic sequence inferred for samples 

collected from the Cone crater ejecta is based on 

interpretations gleaned from small terrestrial craters. 

Studies of these craters have shown that, in a general 

way, the stratigraphy of the target is inverted and 

that younger beds are exposed farther from the source 

in the ejecta blankets. Application of these general 

rules to the Imbrium basin is perhaps an unwarranted 

extrapolation, and we cannot be fully confident that 

ejected materials from such large basins will behave 

in the same way. However, it is noteworthy that the 

samples collected 550 km from the rim of the Imbrium 

basin, and only 150 km from the mapped edge of the 

ejecta deposit, are of a character suggesting a relatively shallow origin. 

Glassy materials in the F 2 rocks were presumably 

produced during the Imbrium event and give little 

information on the lithologic character of the source 

material. The mineral microclast population, however, 

offers more potential. We have pointed out before that 

these clasts are too large and too numerous to have 

been supplied by disaggregation of the most abundant 

(fine-grained metaclastic rocks) clasts in the breccias. 

Early results from Apollo 15 (Wilshire and others, 

1972) show that coarser rocks of appropriate composition were present in the Imbrium target area and that 

these may have supplied the mineral debris if comminution was nearly complete. 

The lithic clasts in the Apollo 14 rocks are of a great 

variety, indicating a very complex target area of the 

Imbrium impact. Igneous clasts include fresh basalts 

of several varieties that are in general richer in feldspar than basalts from the mare regions and rocks 

with cumulus and hypautomorphic textures that suggest igneous crystallization and differentiation at 

depth. Metamorphic clasts, the dominant clast type in 

Apollo 14 rocks, are of both fine-grained dark-colored 

types and coarser light-colored types. All of them 

appear to have formed by impact fragmentation and 

thermal metamorphism, clasts of each type containing 

relicts of the fragmentation and incomplete reequilibration of materials during thermal metamorphism. 

Both the igneous and metamorphic rock types are 

themselves clasts in the common compound breccia 

clasts. In the record revealed by small thin sections, 

as many as four fragmentation events have been 

recognized, each apparently followed by thermal 

metamorphism. These relations show that impact 

fragmentation and subsequent thermal metamorphism 

happened many times and that materials similar to the 

Fra Mauro Formation were themselves disrupted by 

the Imbrium event. It seems likely that the Serenitatis 

blanket, which must certainly have covered most of 

the Imbrium basin area (fig. 14), provided one generation of these materials. 

Hence, the pre-Imbrium terrane, presumed to have 

existed prior to about 3.9 to 4.2 billion years ago 

(Silver, 1971, 1972; Wasserburg and others, 1971) 

was already exceedingly complex. Multiple ejecta blankets from very large impacts had been laid down and 

metamorphosed. Basalts had been erupted and incorporated in the ejecta blankets. Very likely, some flows 
REFERENCES CITED 25 

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s 

FIGURE 14. - Map showing main outer mountain rings of 

major lunar basins, their relative ages, and the extent of 

their continuous ejecta blankets (based on a Mare Orientale 

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Imbrium area or in still older basins, igneous intrusion, crystallization, and differentiation had occurred. 

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*GP078t•165