EARTH AND PLANETARY SCIENCE LETTERS 13 (1971) 61 - 70. NORTH-HOLLAND PUBLISHING COMPANY PETROLOGY OF APOLLO 11 SAMPLE 10071. A DIFFERENTIATED MINI-IGNEOUS COMPLEX M.J. D R A K E and D.F. W E I L L Center for Volcanology, University of Oregon, Eugene, Oregon 97403, USA Received 6 September 1971 Revised version received 28 October 1971 Sample 10071, 33 is a thin section of Apollo 11 ferrobasalt showing an unusual dual texture. The major portion of the sample is very similar to other fine grained Apollo 11 basalts, but the thin section also includes material with a distinct variolitic texture. The two areas are separated by a sharp boundary and the mineralogy and composition of the two textural types are quite distinct. The mineralogy and chemistry of the variolitic portion show it to be the product of rapid cooling of a liquid, intermediate between the typical Apollo 11 ferrobasalt and the associated Si and K-rich mesostasis. This liquid is the result of fractional crystallization of a magma of composition closely corresponding to the major portion of the 10071 system, followed by crystal-liquid separation. The sample provides strong and direct evidence for igneous differentiation on the lunar surface. 1. I n t r o d u c t i o n The discovery o f rocks w i t h unmistakably igneous textures at f o u r locations on the lunar surface (Apollos 11, 12, 14 and L u n a 16) has p r o m p t e d a t t e m p t s to explain their chemical variation in terms o f crystalliquid differentiation processes [2, 3 and m a n y others]. On line of investigation a t t e m p t s to relate the sampled igneous rocks to parent material(s), as yet unsampled and presuma.bly within the lunar interior, via differentiation processes such as partial melting. But the inferred presence o f m a g m a at the surface makes it likely that c r y s t a l - l i q u i d separation processes (gravitative settling, flow c o n c e n t r a t i o n mechanisms, filter pressing, etc.) at or near the surface have also played a role in the final stage o f d e v e l o p m e n t o f the igneous rock suites. This is considered all the more likely w h e n the low viscosity o f the liquids and the substantial density contrast b e t w e e n lunar silicate liquids and crystalline phases are taken into a c c o u n t [ 1 ]. Nevertheless, there is very little direct textural evidence, e.g., layering or banding, flow patterns, size sorting, etc., in the returned igneous rocks to confirm such expectations. In addition, the relatively small range o f chemical variation o f the major elements in the igneous rocks Table 1 Chemical composition of lunar igneous rocks (major elements) from three mare locations. The standard deviation of individual rock analyses from the average concentration is given for the Apollo 11 and Apollo 12 locations. Apollo 11 (16 rocks) Apollo 12 (17 rocks) Luna 16 Avg. S.D. Avg. S.D. SiO 2 TiO 2 A1203 FeO MgO CaO Na20 K20 MnO Cr203 P2Os 40.44 11.15 9.57 19.00 7.36 11.07 0.46 0.18 0.26 0.33 0.13 0.96 1.03 1.20 0.78 0.71 0.66 0.06 0.12 0.03 0.08 0.05 45.02 3.35 9.19 20.55 10.94 9.80 0.29 0.06 0.27 0.49 0.10 1.34 0.87 1.38 1.04 3.37 1.31 0.11 0.01 0.01 0.20 0.03 Total 99.95 Refs. [26-32] 100.06 [33-39] 43.8 4.90 13.65 19.35 7.05 10.40 0.33 0.15 0.20 0.28 100.11  from any one locality (table 1) seems to speak against a major role for c r y s t a l - l i q u i d differentiation mechanisms on or near the lunar surface. 62 M.J.Drake, D.F. Weill, Lunar sample 10071 The conflict between theoretical expectations and observations may be resolved if it is assumed that the returned igneous rocks represent a sampling of only the upper portions of lava ponds or flows. Thus, rapid cooling and crystallization from supersaturated melts would preclude any appreciable crystal liquid separation and the development of textures indicative of flow or crystal settling. Alternatively, the igneous rocks may be the result of small impact events producing much more limited volumes of melt which are rapidly cooled. The difference between these two alternative views is gradational and involves for the most part a difference in the volume of liquid, and hence in the cooling rate during crystallization. The former hypothesis is usually favored. The most direct answer to the problem will come with positive identification of a continuous igneous rock outcrop (such as a lava flow unit or sill) on the lunar surface. Less directly, the formation of the igneous rocks from relatively large bodies of liquid is indicated when their chemical variation is compatible with simple fractional crystallization of a common liquid. For example, most of the Apollo 12 igneous rocks can be related to each other in terms of olivine and/or pyroxene separation [2, 3]. Unfortunately, this approach is somewhat weakened by the relatively small range of chemical variation of the major elements observed in the igneous rocks. None of the late stage differentiates often observed in terrestrial igneous complexes have not yet been found among the suites of lunar igneous rocks. In contrast, there is much evidence of intrasample fractional crystallization leading to a silicicpotassic residual liquid which forms a mesostasis in nearly all of the rocks. The comparatively small volume of this residuum and its extremely high viscosity  make it unlikely that it would be separated from its parental material except under unusual conditions favoring filter pressing. The granitic component of sample 12013 [5,6] may have originated in such fashion, but the evidence is only circumstantial. Despite the theoretical likelihood of differentiation by crystal liquid fractionation, no compelling evidence of such a process has yet been observed. Igneous rock 10071 has been described in general terms as a lunar basalt containing vesicles anf vugs . It was also noted [7,8] that the rock contained two contrasting (coarse vs. fine grained) textural domains. The fine grained portion of the rock was tentatively attributed to recrystallization after flash heating , an essentially isochemical change, but no further petrographic study of 10071 has been reported. A review of our petrographic analysis of sample 10071 indicates that the two textural domains represent subsystems that are probably related by fractional crystallization. If so, sample 10071 provides a direct indication of the efficiency of fractional crystallization as a differentiation mechanism of the lunar surface. 2. General description Thin section 1007 i, 33 is separated by a sharp boundary into areas of relatively coarse and fine texture (fig. 1). Electron probe analyses reveal that the two areas are also quite distinct chemically and mineralogically; the coarser section being very similar to many of the Tranquillity site basalts already described, whereas the finer grained portion is more acidic and is logically interpreted as having crystallized from a liquid fraction which was residual after partial crystallization of a magma of composition closely corresponding to that of the coarser grained material. 2.1. Coarse grained area The coarse grained area has an average grain size of 1 0 0 - 2 0 0 #m. Ilmenite is the dominant opaque phase, and it sometimes encloses armalcolite . It occurs in a variety of habits ranging from tabular to,very thin and platy (often acicular in section). Troilite, usually enclosing blebs of metallic iron, occurs in accessory amounts. The most common silicate is titanaugite, commonly zoned to ferroaugite. Olivine cores are occasionally present within the pyroxenes. Plagioclase is abundant and frequently tabular, probably indicating relatively rapid growth. Interstitial residual material, with its characteristic brown, mottled appearance and high K and Si content is common throughout this area. Silica is also present as a minor phase. A modal analysis of the area is given in table 2. 2.2. Fine grained area The texture of this area is dominated by sheaf-like intergrowths of clinopyroxene and plagioclase and may be classified as variolitic (fig. 1). Individual crystals in these intergrowths are acicular with typical M.J.Drake, D.F. Weill, Lunar sample 10071 I m m 63 . Fig. 1. Photomicrograph of 10071,33 showing the two distinct textural domains. Table 2 Modal analyses (volume percent) of coarse and fine grained areas of 10071, 33 obtained on electron microprobe. Plagioclase Augite Ferroaugite and pyroxferroite Pigeonite Olivine llmenite and other opaque phases Silica K and Si-rich residuum Total Number of points Point interval (~m) Coarse Fine 23.5 38.5 13.0 2.0 1.0 15.5 0.5 6.5 100 400 100 35.5 14.5 29.0 1.0 0.0 4.0 7.5 8.5 100 400 20 dimensions of 1 - 5 / a m by 1 0 0 - 1 5 0 / a m . Some tubular plagioclase and the more equant clinopyroxene of the type found in the coarse grained area are also found here. Much of the augite in this area is strongly zoned to iron-rich compositions all the way into the pyroxferroite composition field, whereas such extreme zoning is u n c o m m o n in the coarse grained area. The small grain size makes it difficult to detect optically any sharp boundary between the clinopyroxene and pyroxferroite, llmenite is the major opaque phase, but it is much less abundant here than in the coarse grained area and occurs only as thin plates. No olivine was found, but the silica and potassium-rich residua are appreciably more abundant in this area. The mode is given in table 2. M.J.Drake, D.F. Weill, Lunar sample 10071 64 3. Analytical results 4 (o) Electron probe analyses for 8 or 9 elements have been made of the major phases and also of the bulk chemistry of the fine and coarse grained areas using a defocussed beam technique. The details of our standard operating conditions and correction procedures are described in . The REE contents of the phosphates (table 3) were obtained from direct comparison with a rare earth lithium metaborate glass standard after only a background correction. Most of the Table 3 Abundances of REE in apatites of 10071,33 (wt%). Counting precision * [25, p. 279] is the major source of uncertainty for these low concentration analyses. 0 8 , >Z w o w 8 ~ La Ce Pr Nd Sm Eu Gd Dy Er 2 3 4 5 6 0.12 0.31 0.05 0.26 0.09 0.01 0.16 0.12 0.06 0.42 1.02 0.22 0.79 0.25 0.10 0.39 0.34 0.30 0.40 0.82 0.16 0.89 0.26 0.02 0.44 0.35 0.25 0.29 0.76 0.14 0.76 0.22 0.04 0.33 0.19 0.09 0.25 0.58 0.14 0.60 0.17 0.01 0.22 0.12 0.08 0.12 0.19 0.03 0.23 0.08 0.02 0.12 0.16 0.13 1 - 3 , coarse grained area. 4-6, fine grained area. * o = 5% relative at 1.0'~ concentration, 30% relative at 0.1% concentration, 200% relative at 0.01% concentration. compositional data graphically reported are partial analyses, showing solid solution variation of the two or three major cations. For each phase type the elemental ratios in the partial analysis are obtained by applying minor empirical correction factors to the background corrected counts. The correction factors are obtained directly from representative complete analyses of the phase in question. 3.1. Opaque phases Analytical evidence  indicates that the amount of Mg entering ilmenite is controlled largely by the Mg/Fe ratio in the coexisting liquid. This has been confirmed experimentally for ilmenites grown at successive stages of fractional crystallization of a liquid corresponding to an Apollo 1 l basalt composition (G. McKay, personal communication). The large range of Mg concentration and its strong correlation with , . , ............. (e) o 4 . ( d ) ~ 0 '" ............. ' ' 2O 16 12 8 4 °o 1 nSn IITTlIT~liNIIi , (b) 4 o ~ , 02'd4'&'o'B' ID WEIGHT % MAGNESIUM Fig. 2. Frequency distribution of Mg in ilmenites in 10071, 33: (a) coarse grained area, ilmenites completely surrounded by ferromagnesian silicates, 6 grains. (b) coarse grained area, ilmenites largely surrounded by ferromagnesian silicates, 27 grains. (c) coarse grained area, ilmenites largely surrounded by plagioclase feldspar, 20 grains. (d) coarse grained area, ilmenite laths less than fifteen microns across, 10 grains. (e) fine grained area, 20 grains. (4) indicates the average Mg concentration. the crystal habit of ilmenite in sample 10022, 28 was used to demonstrate the extended crystallization range of ilmenite from Apollo 11 basalts [ 1]. Fig. 2 shows the frequency distribution of Mg analyses and the strong correlation with the various modes of occurrence of ilmenite in 10071. Throughout the coarse grained area the ilmenite shows a continuous decrease in Mg from those grains which are included in pyroxene (and presumably crystallized prior to their hosts) to the late ilmenite occurring as thin plates. The ilmenites of the fine grained area, on the other hand, are uniformly low in Mg, indicating that they crystallized from a differentiated liquid with lower Mg/Fe ratio. Reid et al. [i 1] reported a similar behavior in the Ni and Co content of iron metal from Apollo 12 basalts. The Ni content of iron in 10071 was investigated with this observation in mind, but no systematic difference between the two textural areas was detected. This was not unexpected since most of the iron in both areas of 10071 is associated with troilite and M.J.Drake, D.F. Weill, Lunar sample 10071 probably crystallized from an iron sulfide liquid which separated from the silicate liquid late in the overall crystallization sequence of both systems [ 12]. 3.2. Plagioclase feldspars Plagioclase exhibits little zoning and has essentially the same composition range in the two areas (An73_ 8 l)Some analyses of plagioclase from the pyroxeneplagioclase sheafs in the fine grained area range down to An6s , but the very thin nature of these crystals makes them difficult to analyze precisely. The potassium content is relatively low in both areas (Or~.o_l. s)In addition to the obvious distinction in crystal habit (fig. 1), the main difference between plagioclase in the two areas is its markedly greater abundance in the fine grained area (table 2). This suggests a differentiation sequence in which the liquid that solidified to give the fine grained texture was separated from the main portion of the system prior to the onset of plagioclase crystallization. Feldspars from a number of Apollo 11 and 12 igneous rocks depart systematically from ideal stoichiometry [ 1 , 4 and 13]. In fig. 3 we plot the analytical results for plagioclase in sample 10071. Analyses of Stillwater feldspars are also shown for comparison because they have grown from slowly cooling liquids and should conform to the usual stoichiometry. They 0.16 0ll4 012 OllO ~ 008 006 I ~, 0 0 4 002 -0.0 IDEAL STOICHIOMETRY 0 ~...~ ~g~,~.k'~,oo~2,2s I 0.02 004 0.06 0 0 8 0.10 012 014 I- (AI- C o - F e - M g ) ASE 016 0.18 0.20 0.22 Fig. 3, Departure of plagioclase analyses from stoichiometry. Chemical symbols represent number of atoms relative to eight oxygens. Based on counting precision, an error of -+0.02 (1 o) is associated with each point for both axes. Symbols: ×, 10071, 33; u, Stillwater Intrusion. 65 were analyzed at the same time as the plagioclase of 10071 with exactly the same set of reference standards and correction procedures. The plot of the Stillwater feldspars indicates the scatter about ideal stoichiometry that can be expected from the analytical technique. The departure from stoichiometry for the 10071 plagioclase is seen to be comparable to that found in other Apollo 11 samples. For example, the average of 30 plagioclase analyses from sample 10022 corresponds to the chemical formula (Cao.744Feo.o32 Mg0.o22, Nao.E0sKo.o 14)1.02o(Si2.32A11.62)3.9408 . On fig. 3 this analysis would plot at coordinates (Si-Na-K)-2 = 0.098 and 1-(A1-Ca-Fe-Mg) = 0.178. No systematic differences in plagioclase stoichiometry were found between the two textures. The observed composition trends reveal a substantial departure from the normal plagioclase chemistry. The norm in this context is taken as a tetrahedral framework, derived from the silica structures, where from one fourth to one half of the tetrahedral cation sites are occupied by A13+. Incorporation of larger univalent or divalent cations (predominantly Na ÷ and Ca 2+) in sites interstitial to the tetrahedral framework is associated with the A13+~ Si4+ substitution to preserve electroneutrality. Within this context, stoichiometry requires that: Na + Ca = 1, A1 + Si = 4, S i - Na = 2, and A I - C a = 1 (the numbers of atoms are normalized to 8 oxygens, and each element symbol is generalized to include all cations of equal valency which enter equivalent structural sites, e.g., 'Na' = Na + K, 'Ca' = Ca + Mg + Fe 2÷, etc.). It is common practice in evaluating chemical analyses of feldspars to calculate only the first two sums above, but this is not a complete test of stoichiometry since three out of the four equations are independent. Several workers [ 1 4 - 1 9 ] have discussed certain aspects of non-stoichiometry observed in terrestrial and synthetic feldspars. An excess of Si over A1 call be accommodated in feldspars according to Si 4+ +  = A13++ Na ÷ or 2Si 4+ +  = 2A13+ + Ca 2+, i.e., by creation of vacancies in the large cation sites. Such a mechanism results in a feldspar chemical formula which can be expressed either in terms of excess dissolved SiO2 or the Schwantke molecule, Cal/2AISi308. Chemical analyses [ 1] indicate that this is not the cause of non-stoichiometry in the lunar plagioclases. Vacancies in large cation sites is only a special case among the possible defects leading to feldspars which depart from ideal stoichiometry. M.J.Drake, D.F. Weill, Lunar sample 10071 66 Vacancies in tetrahedral cation or in oxygen sites and the possibility of limited stuffing of cations in nonstructural positions may also have to be considered in attempting to explain the systematic departure from stoichiometry shown by lunar plagioclases. It is impossible to attempt a solution to this intriguing problem with no more than analytical chemical data. The latter can serve to indicate the problem and define the chemical constraints, but only a structure-sensitive technique (such as X-ray diffraction structural refinement) is capable of discovering the cause of the nonstoichiometry. The genetic implications are that this phenomenon is perhaps related to rapid growth of plagioclase under special lunar surface conditions. 3.3. Olivine, pyroxene and pyroxferroite Analyses of these phases reveal a distinct contrast between the two areas. Olivine is found in the coarse grained portion, occurring as cores surrounded by augite which zones progressively outward into ferroaugite or subcalcic ferroaugite. Occasionally, thin lamellae of pigeonite are observed in the augite, and infrequently pigeonite occurs as a core in place of olivine. Figs. 4a and 4b show the partial analyses (Mg, Fe and Ca) of the ferromagnesian silicates recorded during the modal analysis of the coarse and fine grained areas respectively. The average Fe/Mg DI . . . . ratio of these phases is greater in the fine grained portion than in the coarse grained portion. Extreme zoning from ferroaugite to compositions approaching pyroxferroite is common in single grains of the finegrained area. A series of analyses along such a grain is plotted in fig. 4c. 3.4. Residual phases Both areas contain phases which can be classified as late-forming or residual phases on the basis of texture and chemistry. The composition of these phases is similar in the two areas, but they are more abundant in the fine-grained area. Much of the residual material is glassy or microcrystalline with over 70 wt % SiO2, and is very similar to the Si and K-rich intergranular material found in many other Apollo 11 igneous rocks. Patches of essentially pure SiO2 are also common. The intergranular material of both textures also contains common apatite grains and less common zircon. Three apatite grains from each of the two areas were analyzed for La through Er and the results are presented in table 3. The range of REE concentration indicates an enrichment o f several orders of magnitude relative to chondritic abundances and is similar to the range found in apatite from rock 12013 . There is no systematic difference in the REE concentrations between apatites from the two areas. +5+4, ' ; ¢+b** /,o, o......... \ ~"~ ++:l:++ +~*,t +¢+, ~ ++ ~+ ++ / PC) DI HD +++ ++ ++ .+ . . . \ \ +% . . . \ FE HD i MG IO +:5 \ ~ . ~ FE Fig. 4. Ferromagnesian silicates in 10071, 33: (a) Chemical variation in coarse grained area, 105 points. (b) Chemical variation in fine grained area, 84 points. (c) Analyses at 10 # intervals along a composite ferroaugite-pyroxferroite crystal in fine grained area. 67 M.J.Drake, D.F. Weill, Lunar sample 10071 Table 4 Chemical analyses of coarse grained and fine grained areas of 10071. Whole rock 1 SiO2 TiO 2 A1203 FeO MgO CaO Na20 K/O 42.2 12.34 7.82 17.5, 16.3 0.41 Average whole rock 2 40.93 11.68 7.93, 8.50 19.17 7.30 10.07 0.49 3 13.8 10.9 0.53 0.33 Total 4 Coarse grained mode probe 5 6 Fine grained 7 41.6 12.6 8.1 17.7 7.3 10.5 0.48 0.33 43.1 9.2 9.6 16.8 7.5 13.0 0.55 0.26 42.2 10.2 9.7 16.5 7.7 11.3 0.64 0.44 46.9 4.8 14.5 15.4 3.3 10.8 0.66 1.02 98.61 100.01 98.68 97.38 1. Goles et al. . 2. Goles et al. . 3. Gast and Hubbard . 4. Average of 1, 2, and 3.5. Calculated from mode of coarse grained area. 6, 7. Defocussed beam electron microprobe analyses. 3.5. Major element chemistry There are no complete major element chemical analyses of sample 10071 in the literature, but partial amalyses [ 2 1 - 2 3 ] have been assembled in table 4. These data are labeled 'whole rock', but the sample distribution scheme for 10071 analysis and the relative volumes of the fine and coarse grained areas indicate that the analyses are primarily representative of the composition of the coarse grained area. The composition of this area was also calculated from its mode by using average compositions of the major phases (column 5, table 4). Further control on the composition of this portion of 10071 was obtained by defocussed beam electron probe analysis. Considering the necessary approximations involved in arriving at the composition of the coarse grained area by any of these methods, the agreement (columns 4, 5 and 6 of table 4) is satisfactory. The bulk composition of the fine grained area was also obtained by the defocussed beam technique (column 7, table 4). A comparison of the major element chemistry of the two areas reveals significant contrasts which can be summed up in terms of various compositional parameters: SiO2, 46.9 vs. 42.2; TiO2, 4.8 vs. 10.2; FeO/MgO, 4.7 vs. 2.1; A1203/ CaO, 1.34 vs. 0.86; K 2 0 / N a 2 0 , 1.54 vs. 0.69 (fine grained vs. coarse grained based on wt %). 4. Discussion The crystallization sequence for Apollo 11 ferrobasalts has been determined experimentally and from textural studies [1,8, 24 among others]. In general, it has been found that ilmenite begins to crystallize at relatively high temperatures and continues to crystallize to near solidus temperatures, its Mg content progressively decreasing during the sequence. Olivine also forms early, but its crystallization is interrupted by a peritectic reaction involving liquid and clinopyroxene. The pyroxene is initially Ca-poor pigeonite while augite forms at lower temperature. Although the details of the pyroxene relations are complicated and not yet fully understood, it is well established that there is a progressive decrease of the Mg/Fe ratio in the crystallization sequence. Of the major phases, plagioclase forms last in the sequence, followed b y residual phases such as potassic feldspar, phosphates, zircons, silica and glass. The extreme zoning of the pyroxene indicates poor equilibration between crystal phases and residual melt. Within the context of the generalized crystallization history described above, the mineralogical and chemical contrasts between the two textural types in rock 10071 are precisely what would be expected if the 68 M.J.Drake, D.F. Weill, Lunar sample 10071 fine grained, variolitic portion formed from a liquid which had separated from a partly crystallized portion of 10071 magma. The coarse grained portion of the sample now represents the solidified bulk 10071 magma. Separation of the liquid differentiate took place after the olivine-pyroxene peritectic and prior to the onset of plagioclase crystallization, when the precipitating pyroxene had an intermediate Fe/Mg ratio. Such a mechanism accounts for the absence of olivine in the fine grained area, whereas all other phases are present in both areas, llmenite and pyroxene had been crystallizing prior to separation and although they would be expected in both areas, they should occur in greater concentration and have a higher average Mg content within the coarse grained area. Plagioclase and residual phases would also crystallize in both systems, but they should be more concentrated in the fine grained area. Because of limited liquid-solid reaction after crystals have formed, the composition of plagioclase and residual phases would be almost the same in both systems. The higher concentration of SiO2 in the differentiated, now fine grained, system is almost entirely accounted for by the large contrast in ilmenite (early forming) and silica (probably the last phase to crystallize) content of the two areas. Rock 10071 is a composite sample presenting very strong evidence for igneous differentiation by fractional crystallization followed by solid-liquid separation. The fine grained differentiate is intermediate in composition between typical Apollo l 1 ferrobasalt (typified by the coarse grained area) and the more strongly differentiated mesostasis found in virtually all of the Tranquillity basalts. A liquid corresponding in composition to the mesostasis material has a viscosity in excess of 107 poises at 1100°C , and it would require special conditions to effectively separate it from its almost completely solidified surroundings. It is unlikely that such a process was important during the crystallization of surficial lava flows for there is little direct evidence for it (e.g., veinlets or other segregations of mesostasis material) in any of the lunar igneous rocks collected so far. The only possible exception is the granitic portion of Apollo 12 sample 12013 which may be interpreted as a segregation of strongly differentiated residuum by means of filter pressing . Separation of intermediate liquids such as that which gave rise to the fine grained portion of 10071 is perhaps easier to effect due to its greater abundance and much lower viscosity of less than 104 poises at 1100°C . The scale and extent of such solid liquid separation is still a matter for conjecture. There is strong evidence that the two portions of 10071 are related by crystal-liquid fractionation, but the details are subject to several interpretations. The separation of the intermediate liquid may have taken place in some common interior (but most likely shallow) magma source or it might be the result of movements within a flow or lava pool at the surface. Certainly the two portions of 10071 need not have been part of the same surface flow unit, although the simplest explanation would involve autoinjection of the intermediate liquid into already solidified portions of a lava flow or crusted lava pond. Most importantly, however, sample 10071 provides us with strong and direct evidence that differentiation via crystal-liquid separation did occur during lunar igneous activity. The sample also suggests that at least some of the variations in texture, mineralogy, and chemistry observed in lunar rocks, breccias, and smaller fragments need not always be related to very large scale differentiation or to different parental magmas. Finally, we would like to suggest that an investigation of the minor and trace element abundances in the two areas of sample 10071 would be a rewarding companion exercise. Acknowledgments The authors gratefully acknowledge the support of National Aeronautics and Space Administration grant NGL 38-003-022. References [ 1] D.F. Weill, I.S. McCallum, Y. Bottinga, M.J. Drake and G.A. McKay, Mineralogy and petrology of some Apollo 11 igneous rocks, Geochim. Cosmochim. Acta, Suppl. 1, Vol. 1 (1970) 937.  I. Kushiro and H. Haxamura, Major element variation and possible source materials of Apollo 12 crystalline rocks, Science 171 (1971) 1235.  G.M. Brown, C.H. Emeleus, J.G. Holland, A. Peckett and R. Phillips, Picrite basalts, ferrobasalts, feldspathic norites, and rhyolites in a strongly fractionated lunar crust, Geochim. Cosmochirn. Acta, Suppl. 2, vol. 1 (1971) 583. M.J.Drake, D.F. Weill, Lunar sample 10071  D.F. Weill, R.A. Grieve, I.S. McCallum and Y. Bottinga, Mineralogy-petrology of lunar samples. Microprobe studies of samples 12021 and 12022; viscosity of melts of selected lunar compositions, Geochim. Cosmochim. Acta, Suppl. 2, vol. 1 (1971) 413.  M.J. Drake, I.S. McCallum, G.A. McKay and D.F. Weill, Mineralogy and petrology of Apollo 12 sample no. 12013: a progress report, Earth Planet. Sci. Letters 9 (1970) 103.  O.B. James, Petrology of lunar microbreccia 12013, 6, U.S. Geol. Surv. Int. Rep. Astrogeology 23 (1970) 1.  H.H. Schmitt, G. Lofgren, G.A. Swann and G. Simmons, The Apollo 11 samples: Introduction, Geochim. Cosmochim. Acta, Suppl. 1, vol. 1 (1970) 1.  E. Roedder and P. Weiblen, Lunar petrology of silicate melt inclusions, Apollo 11 rocks, Geochim. Cosmochim. Acta, Suppl. 1, vol. 1 (1970) 801.  S.E. Haggerty, F.R. Boyd, P.M. Bell, L.W. Finger and W.B. Bryan, Opaque minerals and olivine in lavas and breccias from Mare Tranquillitatis, Geochim. Cosmochim. Acta, Suppl. 1, vol. 1 (1970) 513.  J.F. Lovering and J.R. 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