A merican M ineralog is t, Volwne 6 3, pages 92 4 -9 29, I 97 8 Implicationsof a titanium-richglass clod at OceanusProcellarum Unsule B. MenvtN H aruard- S miths onian C ente r fo r A strophysi cs Cambridge,M assachusetts 02I 38 lNp Devto Wnlrrn Departmentof Geology,Haruard Uniuersity Camb ridge, M assachuset ts 02 I 38 Abstract A friable clod consistingof spherulesand conchoidalfragments of red-blackglass with an exceptionallytitanium-rich composition (-16 percentTiOr) was discoveredin the 2-4 mm fractionof Apollo l2 sample12033. Despite a diligentsearch of the remainingApollo l2 soils, no similarfragment has beenfound in the samplesfrom that or any other lunar mission.By analogywith the glassspherule clods collectedat the Apollo 15 and Apollo 17 sites,this uniqueclod of glassmay representa lunar magmaof which no crystallineequivalent has yet beenfound. The probabilityis smallthat magmaswith the compositionof the red-blackglass could be parentalto high-K titaniferousApollo I I basaltby low-pressurefractional crystallization. Red-blackglass composition cannot be parentalto any other lunar basalttypes. If red-black glassis a magmatype, and not an accidentallyremelted cumulate, its existencerequires that gross heterogeneityof TiO, characterizelunar magmasource regions and/or that simple modelsof magmagenesis cannot produce this type. Occurrence suggestan affinity with mare basaltsrather than no- rites. A friable spheruleaggregate, which looked like a When the clod was discoveredin the summerof dollopof blackcaviar (Fig. I ), wasrecognized as an 197l,it wasimmediately mounted in epoxyand cut exceptionalparticle of lunar soil during a macro- into a thin section.As no more of the clod remains, scopicsurvey of Apollo 12 sample 12033,66.The the opportunitywas thus lost to treat this 2-mm samplerepresented a layerof light gray soil that was particleas a consortiumrock (an approachthat was exposedat a depthof a few centimetersin the wallsof developedlater) in order to determineits age and a trench the astronautsdug through the rim of Head trace elementcontent and to analysethe spherule Crater.The light color of the soil signaledan abun- surfacesfor micromoundsof condensedvolatiles, as danceof small ropy fragmentsof KnErp-richglass wasdone subsequently on theApollo l5 greensphe- coatedwith gray-whitedust. The ropy glasseshave rulesand the Apollo 17orange and black spherules beeninterpreted as either ray materialfrom the crater (for reviewsee Butler and Meyer, 1976). Copernicus(Meyer et al., l97l) or as shock-melted A singlesoil particle,regardless of how exotic its ejecta from a more local impact crater that pene- composition,hardly seemsadequate for formulating trated thin mare flows and excavatednoritic materi- a petrogenetichypothesis. In order to find additional als (Quaide et al., l97l). Although the dark clod, examplesto be usedfor surficialanalyses and other which differedstrikingly in textureand composition studies,an arrangementwas madeby U. B. Marvin from all other particlesin the Apollo 12 soils,oc- in 1977to examineand catalogue the Apollo l2 soils curredin a sampleconsisting of 40 percentropy glass in storagein the CuratorialFacility at Houston(cata- fragments,no geneticassociation between these par- logue in preparation).A diligent searchof all the ticle types need be assumed.On the contrary, high fractions coarserthan 0.55 mm failed to locate a valuesof titanium and chromiumin the dark glasses single spheruleor spheruleaggregate of red-black 0003-004x/7 8/09 I 0-0924$02.00 924 MARVIN AND WALKER' TITANIUM-RICH GLASS CLOD 92s glass.Inasmuch as no similarclod has been found in -'r'i'ti anyother lunar soil, the original clod remains unique. Texture In thin sectionthe clod is nearlyopaque in trans- mittedlight, but the extraillumination provided by a substagecondenser shows that the main constituent is a very dark red-blackglass. A single50-pm frag- ment of clinopyroxeneis locatednear the centerof the section,but most if not all of the many other small transparentphases are crystallitesof olivine and pyroxene.Reflected light (Fig. 2a) revealsthat the clodis a porousaggregate of spherules(5- I 30pm dia.), conchoidalspherule fragments, and irregular chunks of glass.Some of theseglass chunks and partially devitrifiedfragments of spheruleshave been compressedtogether into new aggregates,but clasts incorporatinglithologies other than red-blackglass and its partial devitrificationproducts were not ob- served.About 35 percentof the glassyparticles are brownishin colorand contain well-developed crystal- lites of ilmenite,olivine, and/or pyroxenewith a maximumsize of 2.5x 1.4pm (Figs.2b,2c,2d). The remaining65 percentof the spherulesand fragments are dark red and cloudy,with opaquesubmicron Fig 2. Views in reflected light of the polished thin section ofthe crystallitesdistributed uniformly or alignedin feath- glassy clod. (a) View of the entire particle showing the distribution erypatterns in theglass. The presence of theseminute of spherules in the porous matrix of conchoidal glass fragments. pre-existing portion crystallitesgives the dark glassesan exceptionally The dark diagonal streaks are fractures. (b) A of the section illustrating the contrast between the highly reflective bright reflectivity which makes the mafic silicates spherulesand fragments containing minute, uniformly distributed look dull grayin comparison.This is theopposite of opaque crystallites and the fragments of darker glass with the usual reflectivity contrast betweenglasses and prominent crystallites (c) Two particles with crystallites in maficsilicates. different stages of growth. The particle at the upper left has a delicate dendritic pattern of ilmenite. The one at lower left includes Composition ilmenite crystallites plus one elongated olivine crystallite which occupies the band between the lobe at the left and the larger Electron microprobe analysesof the homoge- portion at the right. The remaining matrix material is brownish neous-appearingdark spherulesand fragmentsshow glass that partially covers the olivine, making it indistinguishable in this photograph. (d) A "homogeneous" spherule and an irregular mass of glass with the more uniform variety grading into the more coarsely crystalline type. thenarrow compositional range listed in TableI and plotted in Figures3 and 4. The red-blackglass is olivine-normativeand containsabout 3l weightper- cent of normativeilmenite. The growth of olivine, ilmenite,and a few clinopyroxenecrystallites in the red-blackglass produces a lighter-colored,quartz- normative, pyroxene-plagioclase-richresidual glass (Table l). Most attemptsto analyzethe crystallites failed to yield mineralcompositions unmixed with glass.However, two good crystalliteanalyses are of olivine(Forr) containing 0.3 percent Cr. Thisvalue of Fig. l The 2-mm clod of spherulesand fragments of red-black chromiumin a lunarrock suggestsa genetic relation- glass from Apollo 12 sample 12033,66. shio with mare basaltsrather than with noritesor 926 MARVIN AND WALKER: TITANIUM.RICH GLASS CLOD Table l. Electronmicroprobe analyses of the glassclod Glassspherules and clods A. The averageand range of valuesin 8 particlesof red-black Impactand volcanism are both glass-forming proc- glass "homogeneous" esses,and both aregenerally believed to havecontrib- B. Bulk compositionof the clod,derived from theaverageof8 100 pm broad-beamanalyses recalculated to 100percent uted glassyparticles to the lunar regolith.To distin- C, The compositionof I particle of brown quartz-normative, guish impact from volcanicglass is sometimesa residualglass containing crystallites of olivineand ilmenite relatively straightforward exercise:impact glasses may havethe compositionof non-igneoustarget ma- terials,whereas volcanic glasses should duplicate or Avg. Range showa closegenetic relationship to the compositions of volcaniclavas. It becomesmore dimcult to distin- - ?? nt S102 33.44 31.83 35.14 42.8r guish betweenimpact and volcanic origins when T102 ro.J/ ro.uz - ro./o r). oo 10.54 glassyparticles are the product of impacts into ig- 41203 4.60 3.90 - 5.41 6.2r 5.15 neousrocks or remeltedbreccias with largepropor- Ct20g 0.84 0.71 - 0.98 1.00 0,22 tions of igneousclasts. Particles of eitherimpact or Fe0 23.87 23.42- 24.43 zJ.04 20.88 glass in association ltn0 0.30 0.24 - 0.36 0.30 0.30 volcanic would logicallyoccur Mgo 13.00 12.04 - 13.87 1a <1 8.15 with unmeltedfragments of equivalentcomposition. Ca0 6.27 5.14 - 6.90 6.69 LO.74 Thus many lunar glassesare not easilyclassified. Na20 0.05 0.00 - 0.13 0.15 0.30 Spherulesof clearglass in a wide spectrumof col- Kzo o,r2 0.03 - 0,42 0.40 o.7r ors are ubiquitousin the lunar soils,and thoseindi- N10 0.02 0.00 - 0.06 o.o2 0.03 viduals that mimic the compositionof individual Pzos n.d. 0.20 0.17 mineralsor of bulk soilsare readily ascribedto im- qn^ - v-5 0.08 0.01 0,16 0.r2 0.09 pact. If impact was the processresponsible for pro- spheruledeposits, the highland AOEAI 98.96 100.00 100,09 ducing aggregated soils should include discretelayers or lensesrich in anorthositicgabbros (Marvin et al., l97l). Oneanal- ysis yielded a normative compositionof 94 percent -A PSEUDOTERNARY I II HIGH-K clinopyroxene(EnrrFsnoWols). The singlepyroxene 2'A il,t7LoW-K LIQUIDUS S.ORANGESOIL fragment not occurring as a crystalliteis more Ca- PROJECTION 4'At2 ILM rich (EnarFsroWor,). FROM 5=Lt6 6=At2 PtC-PtG In an attemptto determinethe bulk compositionof CnAL2St2Os 7-A t5 the clod, a numberof 100-pmbroad-beam analyses S.GREENGLASS, L24,VLT were made at random on the section.The