Terrestrial and Extraterrestrial Fullerenes

38 Pages·2003·0.3 MB·English

120025855_FST11_4_R1_090403
FULLERENES,NANOTUBES, ANDCARBON NANOSTRUCTURES
Vol.11,No.4, pp.333–370,2003
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8 Terrestrial and Extraterrestrial Fullerenes
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11 D.Heymann,1,*L.W.Jenneskens,2J.Jehlicˇka,3C.Koper,2
12 and E. Vlietstra2
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1DepartmentofEarthScience,RiceUniversity,Houston,Texas,USA
15 2DebyeInstitute, Departmentof Physical Organic Chemistry,
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UtrechtUniversity,Utrecht, TheNetherlands
17 3Institute of Geochemistry, CharlesUniversity, Prague,
18 CzechRepublic
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22 ABSTRACT
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24 This paper reviews reports of occurrences of fullerenes in circumstellar
25 media,interstellarmedia,meteorites,interplanetarydustparticles(IDPs),
26 lunar rocks, hard terrestrial rocks from Shunga (Russia), Sudbury
27 (Canada) and Mitov (Czech Republic), coal, terrestrial sediments from
28 the Cretaceous-Tertiary-Boundary and Permian-Triassic-Boundary,
fulgurite, ink sticks, dinosaur eggs,and atree char. The occurrences are
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discussed in the context of known and postulated processes of fullerene
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formation, including the suggestion that some natural fullerenes might
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haveformed from biological (algal) remains.
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Key Words: Fullerenes; Stellar media; Moon; Meteorites; Terrestrial
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rocks; Biogenicformation.
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*Correspondence: Dieter Heymann, Department of Earth Science, Rice University,
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38 Houston, TX 77251-1892,USA;E-mail: [email protected]. Q1
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DOI:10.1081=FST-120025855 1536-383X(Print);1536-4046(Online)
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Copyright#2003byMarcelDekker,Inc. www.dekker.com
334 Heymannet al.
43 1. INTRODUCTION
44
45 When Kroto etal.[1] discoveredbuckminsterfullerene, theypredicted that
46 this surprisingly stable carbon molecule should occur abundantly in circum-
47 stellar and interstellar media, hence in meteorites. Astronomers almost
48 immediately began searches for fullerenes and fullerene derivatives in
49 interstellar and circumstellar media. When Kra¨tschmer et al.[2] first synthe-
50 sized macroscopic amounts of C60 and discovered that the fullerenes were
51 soluble in organic solvents such as toluene and in CS2, the search for
52 fullerenes in terrestrial and extraterrestrial rocks became possible and began.
53 All searches had in common not only the excitement of the hunt, but, if
54 fullerenes were found, speculations on how and where these had formed in
55 the first place. There ensued therefore an interesting interaction between geo-
56 and cosmochemists on the one hand and fullerene chemists on the other (see
57 Ref.[3]).Inthisreviewwewillreportthestoryofthesuccessesandfailuresof
58 searches for fullerenes in nature and the interpretations of their formation or
59 absence.
60 Thereaderofpublicationsonterrestrialandextraterrestrialfullereneswill
61 be confronted with apparently conflicting results. For example, one group of
62 investigators reported the finding of fullerenes in samples of the Allende
63 meteorite[4] while others havefailed to find fullerenes in other samples of the
64 same meteorite.[5–10]Wewill never usethe statement‘‘there areno fullerenes
65 intheAllendemeteorite’’butweshallassumethat‘‘groupAfoundfullerenes
66 intheirsamplesofAllende’’or‘‘groupBfoundnofullerenesintheirsamples
67 of Allende’’. Even when there were doubts expressed about a discovery of
68 fullerenes ‘‘in the wild’’ we will treat every discovery as real unless retracted
69 by its authors.
70 We have attempted to find and include most relevant publications up to
71 December 31, 2002, including significant conference abstracts. Occasionally
72 such abstracts are the only reports available on a specific topic. The great
73 majority of abstracts cited are from the annual Lunar and Planetary Science
74 Conferences or the annual Meetings of the Meteoritical Society. The former
75 canbeorderedfromtheLunarandPlanetaryInstitute,Houston,TX,USA;the
76 latter are printed in the regular issues or supplements of Meteoritics (now
77 Meteoritics and Planetary Science) An exception to completeness was made
78 for publications in the fields offullerene photo- and pressure-polymerization,
79 fullerene synthesis by carbon condensation, and fullerene synthesis by oxy-
80 gen-starvedcombustionoforganiccompounds.Thenumberofpapersineach
81 ofthesefieldsissolargethatwedecidedtocullforcitationonlyafewpapers
82 fromeachofthese.Thereferencesectionofthispaperlistsalargenumberof
83 entries. This is deliberately done to ease literature researches of future
84 investigators of fullerenes in nature.
Terrestrialand Extraterrestrial Fullerenes 335
85 2. FULLERENE ASTROCHEMISTRY
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87 Analysis of all manifestations of electromagnetic radiation is the only
88 diagnostic tool that astronomers have to survey for electrons, ions, atoms,
89 molecules, macromolecules and solid grains (‘‘stardust’’) in the Universe.
90 Every conclusion that one of these is discovered must be confirmed by
91 analogous experimental or theoretical studies in the laboratory. Given the
92 huge number of known atoms, molecules, and minerals, inorganic as well as
93 organic,thatseemstobearelativelysimpletask,butitcanalsobefrustrating
94 when more than one molecule or cluster of molecules emits, absorbs,
95 polarizes, or scatters light at or very near the wavelengths of interest.
96 When fullerenes were discovered there already existed a number of
97 enigmatic observations concerning radiation received from interstellar media.
98 Foremostamongthesewerethegeneralshapeoftheinterstellarextinctioncurve
99 fortheGalaxywithitsstrong,butbroadfeaturecenteredat217nm,andtheso-
100 calleddiffuseinterstellarbands(DIBs),whicharespectralfeaturesarisingfrom
101 absorption of light by matter in the diffuse interstellar gas. The strong 217nm
102 absorption band was variously attributed to graphite, carbonaceous materials,
103 carbon compounds processed on icy grains, or carbon onions, but there are
104 problems with all of these (see for example Ref.[11]). Thirty-nine DIBs were
105 knownin1975andabout80in1988.Todaytheynumbermorethan200.Diffuse
106 interstellarbandsrangeinfrequencyfromthevisibletotheinfrared.Avarietyof
107 carbon-bearingcompoundswasproposedascarriers,butthemostwidelytouted
108 of these were ionized PAHs.[12–15] The initial problem with PAHs was an
109 ‘‘embarrassment of riches’’ because it was concluded that the already known
110 PAHs shouldgive risetomany moreDIBsthan observed, unlessone accepted
111 thatonly arestrictednumberofPAHs actuallyoccurred ininterstellar media.
112 Ontothissmorgasbordofastrochemicalcompoundsfellthefullerenesand
113 they, as well as some of their derivatives, immediately became potential
114 candidates for the interstellar extinction curve, its 217nm maximum, and the
115 DIBs. A major observational problem, until after 1990, when macroscopic
116 amounts of C60 became available, was that only one absorption feature of C60
117 at 386.0nm had been determined.[16] All other assignments of fullerenes to
118 specific DIBs had to be checked by theoretical calculations of the unknown
119 energies of electronic and vibrational transitions of fullerenes and fullerene
120 derivatives.Today,theresultsofsearchesforfullerenesininterstellarmediahave
121 achieved very modest, but still much debated results. Perhaps the strongest
122 evidencewasthefitofafewDIBsintheinfraredwithmeasuredabsorptionbands
123 ofC þ[17–24]andoftheinterstellarextinctioncurvewithits217nmmaximum
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124 withC60andfulleranes,thehydrogenatedfullerenesC60H2n(n¼1(cid:1)30).[25–30]
125 However, even in these cases there remained strong reservations about the
126 assignments.[31,32] There were also failures to associate specific DIBs with
336 Heymannet al.
127 known electronic and vibrational transitions of fullerenes and fullerene deriva-
128 tives,especiallyintheUV.[33–35]Astudyoflightemittedfromaproto-planetary
129 nebula concluded that the observed electromagnetic features could be best
130 explained by a mixed population of hydrogenated amorphous carbonaceous
131 grains, fullereneswith different degrees of hydrogenation, partially dehydroge-
132 natedcationicPAHmolecules,andcrystallinesilicates,[36,37]quiteanassortment
133 ofcompounds.Nevertheless,thatisperhapsmuchmorerealisticthanclaimsthat
134 anyspecific,singlecarboncompoundisgreatlydominantinsuchenvironments.
135 If fullerenes occur in interstellar media, how were they formed and from
136 where did they come? The most widely held view is that interstellar fullerenes
137 formedinitiallyinatmospheresofcarbon-rich,hydrogen-poorstarswhencethey
138 are delivered by strong stellar winds to interstellar media. Possible syntheses
139 include carbon condensation,[1,38–42] but also hydrogenation,[25–30] pyrolysis of
140 gaseous molecules,[43] and decomposition of hydrogenated amorphous
141 carbon.[44] Unfortunately, extensive experimental evidence shows that many
142 other forms of elemental carbon are likely to form alongside fullerenes and it
143 is still not understood which of these will be the most abundant in any of the
144 relevant astrochemical environments. Today, mostinvestigatorsofformation of
145 fullerenes in stellar atmospheres consider the simultaneous formation of amor-
146 phouscarbon,carbononions,carbonblack,andcarbynesinvariableproportions.
147 Once delivered to interstellar media, the fullerenes and fullerene deriva-
148 tives participate in the complex chemistry of these environments. Detailed
149 experimentalandtheoreticalstudiesonthissubjecthavebeenpublished.[45–49]
150 The following is a summary of the pertinent observations and conclusions.
151 The high ionization energy of C60 and the low UV flux in interstellar clouds
152 essentially preclude direct photoionization, but charge transfer electron
153 detachment from Heþ or interactions with cosmic ray protons may produce
154 C602þ and C603þ. The most likely loss process for both species is partial
155 neutralizationwithelectrons,eventuallytoC60þ.WhetherC60(cid:1)ionscanform
156 either by free electron attachment or by electron transfer with negatively
157 charged PAHs is not clear. Once formed, however, C60(cid:1) ions should be quite
158 stable given the high electron affinity of the neutral molecule. The three
159 positiveionscanreact,however,withvariousmoleculesininterstellarclouds.
160 Their reactivity decreases from C603þ to C60þ. The reactants studied include
161 C6H6, C20H10, C14H10, CH3OH, HC3N, NH3, and many others. With acenes,
162 the ions, like neutral C60, form [4þ2] cycloadducts. Adduction with con-
163 densedPAHssuchascorannulene,resultsinacharge-transfercomplex.These
164 papers do not present any calculated equilibrium distribution of the various
165 fullerenicmoleculesbecause thatcannotbedonereliablyuntilthereaction of
166 C60withatomichydrogenbecomesbetterstudied.Theysuggest,however,that
167 neutralC60islikelytobethemostabundantfullerenicmoleculeininterstellar
168 media, if such molecules exist there at all.
Terrestrialand Extraterrestrial Fullerenes 337
169 In summary, while there are tantalizing hints, there is no solid evidence
170 that fullerene molecules, ions, or their derivatives actually occur in circum-
171 stellar and interstellar media.The notionthat interstellar mediaare, hencethe
172 solar nebulawas rich in fullerenes, available there in abundance to be picked
173 up by meteorites or their precursor materials is unwarranted.
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176 3. FULLERENES IN ROCKS
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178 3.1. Meteorites and Interplanetary Dust Particles
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180 Soon after fullerenes were discovered it was suggested that they might
181 occur in meteorites as a kind of ‘‘molecular bottles’’ for certain isotopically
182 anomalous trapped noble gases.[50] However, it was subsequently found that
183 these gases were actually contained in nanodiamonds.[51] Nevertheless, pre-
184 ciselybecausethenanodiamondsandthelaterdiscoveredgraphiteandsilicon
185 carbide grains in meteorites are interstellar, it seemed logical to search for
186 possibly interstellar fullerenes in meteorites also.
187 There are three major classes of meteorites: the iron-, stony- and stony-
188 iron meteorites. Elemental carbon occurs in meteorites of all three, but the
189 thermal and metallurgical histories of the iron meteorites, whose metals were
190 once molten and many of which contain graphite, mitigates against them
191 containingfullerenes,andnosearchesforfullereneswereevermadeinironor
192 stony-iron meteorites. Among the stony meteorites it is the carbonaceous
193 chondrites that are the richest in presolar grains, hence are the most likely
194 extraterrestrial rocks to contain presolar fullerenes.
195 The search for fullerenes in rocks is a comparatively simple geochemical
196 procedure. CS2 and aromatic organic solvents were used for the extraction of
197 fullerenesfromrockswhenitbecameunderstoodthatC60andC70dissolvewellin
198 them.Mostanalyticalproceduresbeginthereforewithsolvent-extractionofeither
199 thepowderedmeteoriteoritsso-called‘‘acid-resistantresidues’’(ARRs),carbon-
200 enrichedresiduesobtainedbythedissolutionofinorganicmineralsusuallywith
201 HF-HCl. One assumes thatthe fullerenes are not too strongly locked upin the
202 powdered meteorites or ARRs and that the chemical treatments do not destroy
203 them.StudiesofthegeochemicalbehavioroffullereneshaveshownthattheHF-
204 HCltreatmentsdonotdegradethembutverystronglyoxidizingchemicalssuch
205 ashotperchloricaciddo.[52]Meteoriteextractswerealwaysincontactwithairat
206 some stage of the analysis but in darkness and even in conditions of moderate
207 light (e.g. lab benches) molecular oxygen does not react detectably with full-
208 erenes.However,ozoneswiftlyoxidizesfullerenesinsolution.[53]
209 AfterfiltrationtheextractsareanalyzedbyHPLCorbymassspectrometry
210 (or, as in a few studies, by both). HPLC has the advantage that fullerenes are
338 Heymannet al.
211 neither formed nor destroyed by this technique and that rather precisely
212 calibrated quantitative data can be obtained. A potential problem is that
213 fullerenes and several organic compounds with closely similar retention
214 times and UV-VIS absorption spectra could be present in the extracts. This
215 problem can be alleviated but not completely removed by the use of different
216 HPLCcolumnsfortheanalysisofthesamesample.[10]massspectroscopy,the
217 characteristicsetofisotopicpeaksatm=z¼720–724amuinspectraisusedfor
218 provingthepresenceofC60inthesample,butwhenlaserdesorption-ionization
219 isusedthereisthepotential riskthatfullereneions areactuallyformed inthe
220 process from carbonaceous matter or hydrocarbons. Also, mass spectrometric
221 methods have not yet yielded precise quantitative data. In one study, the
222 extractionoffullereneswasattemptedbysublimationintherange300–600(cid:2)C,
223 followed by mass spectrometric analysis.[7] Two papers reported negative
224 results ofsearches for fullerenes intwo meteoritesbyvacuum pyrolysis.[5,6]
225 Table1presentsasummaryoftheresultsofallsearchesforfullerenes in T1
226 meteorites.Dr.P.Buseck(personalcommunicationofunpublishedresults)did
227 not find fullerenes in twelve carbonaceous and ordinary chondrite samples of
228 his own. Obviously some investigations found fullerenes in their samples
229 whilstothersdidnotintheirs.[4–10,54–58]Itisstillnotclearwhathascausedthe
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Table 1. Reported fullerene contents in meteorites.
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234 Meteorite C (ppm) C (ppm) Highera Reference
60 70
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Allendeb 100 [4]
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Allende detected detected detected [54]
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Allendec all <1 [150,151,157]
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Allende detected detected [55]
239
Allende detected detected detected [54]
240 Allende 10 [56]
241 Allende 10 [56]
242 Allende 5 [56]
243 Allended all <3 [56]
244 Allende detected detected detected [57,58]
245 Murchison notdetect. [5,6]
Murchison <2 [7]
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Murchison notdetect. [157]
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Murray notdetect. [5,6]
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249 aHigher means C>70
250 bArrangedin orderof year ofpublication
251 cAtotalof nine distinct samples
252 dAtotal of sevendistinct samples.
Terrestrialand Extraterrestrial Fullerenes 339
253 differences. Chondritic meteorites are known to be mineralogically hetero-
254 geneous clastic breccias, hence the analysis of one large and homogenized
255 sample, or of a number of smaller samples may be required to find any
256 fullerenes present in a given meteorite. Some of the negative results could be
257 due to inefficient fullerene extraction.
258 It appears then that fullerenes occur heterogeneously distributed in ppb
259 quantitiesintheAllendemeteorite.Ithasnotbeenconvincinglydemonstrated
260 thattheyoccurinothermeteorites.Againthequestionsare:howandwheredid
261 the Allende fullerenes form? It was suggested that these had formed around
262 C-rich stars, had made it into interstellar media and eventually via the solar
263 nebula into the meteorites, [4] but it was also suggested that the formation of
264 fullerenes and fulleranes could have occurred in the solar nebula.[55,56] The
265 mostrecentstudiesreporttheoccurrenceofnoblegasatomstrappedinAllende
266 fullerenemolecules.[57,58]Thecompositionofthetrappedgasisthatofthewell-
267 known meteoritic component of ‘‘planetary noble gases’’, which were sug-
268 gestedtohavebeentrappedinacarbonaceousmeteoriticphaseinthecooling
269 solar nebula.[59] Some, or even all of the fullerene molecules of Allende may
270 thereforehaveformedinthesolarsystembutitisstillunclearhowandwhere.
271 We suggest here that clues may be found in the nature of the carbonaceous
272 matteroftheAllendemeteorite.Inmostcarbonaceousmeteorites,thebulkof
273 the element carbon occurs as a complex organic polymer. Allende is excep-
274 tional because the element is a poorly ordered carbon, characterized from
275 studiesbytransmissionelectronmicroscopyas‘‘glassycarbon’’.[60,61]Amore
276 recent TEM study of Allende carbon supports this finding and reports the
277 abundant occurrence of ‘‘carbon black-like particles’’ Vis et al.[62] Taken
278 together these observations suggest that Allende carbon formed by pyrolysis
279 of hydrocarbons and polymeric hydrocarbons, in part in a gas phase, in part
280 perhapsonhotmineralsurfaces.Suchascenariofortheformationoffullerenes
281 isnottoooutlandishwhenoneconsidersthatfullereneshavebeensynthesized
282 by the pyrolysis of naphtalene[63] and by the consecutive=multiple cyclo-
283 dehydrogenationofevenmorecomplextrimerizedPAHs.[64–69]
284 Ithasbeensuggestedthatpre-terrestrialfullerenesareanimportantcarrier
285 phase for the noble gases of the atmospheres of the terrestrial planets.[57,58]
286 That is questionable because it can be shown that the Allende ARR must
287 contain more than 1g C60 per gram to account for all so-called planetary He
288 and that is obviously impossible.
289 Interplanetary dust particles (IDPs) constitute a circumsolar dust system.
290 It is generally assumed that this system must be continuously refreshed with
291 particles from comets and asteroid collisions. The particles have been
292 collected in the Earth’s stratosphere and by Earth-orbiting spacecraft but
293 also from the mid-oceanic seafloor and polar ice deposits. Interplanetary
294 DustParticlesrangeinsizefromaboutonemicrometertoabout1mm.Itisnot
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295 clear why IDPs might contain fullerenes unless one argues that the collisions
296 of and impacts on chondrite parent bodies in the asteroid belt releases
297 fullerene-bearing chondrite dust. Bajt and his coworkers searched for full-
298 erenes in IDPs.[70,71] The result, although seemingly encouraging, was never-
299 thelessinconclusive.Morerecently,BeckerandPoreda[72]havesuggestedthat
300 IDPs contain noble gas-laden fullerenes.
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303 3.2. Fullerenes were not found on the Moon
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305 The discovery of fullerenes on the skin of the Long Duration Exposure
306 Facility (LDEF) spacecraft in Earth orbit, possibly formed by a high-energy
307 impact from carbon of a micrometeorite,[73] suggested that fullerenes might
308 occur in the lunar regolith, the fragmented and unconsolidated outermost
309 rocky layer of the Moon. Impact craters with a large range of diameters are
310 abundant selenographic surface features and some of the impactors are likely
311 to have contained elemental carbon or carbon compounds from which full-
312 erenes could have formed in some of these violent events. A search for
313 fullerenes in samples returned by Apollo missions was therefore under-
314 taken.[74] Two samples of so-called ‘‘lunar fines’’, i.e. <1mm particles from
315 theregolith,weremadeavailablebyNASA.Onewas5.006goffinescollected
316 directlyatthesurfaceoftheApollo11landingsite.Theother wasa7–17cm
317 depth subsurface sample of 0.972g fines collected in the Van Serg trench at
318 theApollo17site.Thesampleswereextractedwithtolueneandwereanalyzed
319 by HPLC. No fullerenes were detected at the 1ppb level or higher.
320 Thesenegativeresultsmustbeevaluatedinthecontextofthepunyfraction
321 of lunar regolith matter that was actually studied. The regolith content of
322 fullerenes could be grossly heterogeneous with detectable amounts present at
323 youngcratersbutnoneinolderterranesasthereareseveralprocessesthatcould
324 dilute or even destroy regolith fullerenes in the course of time. Elemental
325 carbon,includingfullerenes,canreactwithimpact-moltensilicatestoformCO
326 andCO2thatescapefromtheMoon,oneexplanationforthesurprisinglysmall
327 carbon contents of lunar fines and rocks.[75–78] Also, fullerenes can become
328 destroyed on the Moon by thermal decomposition,[79–81] destruction by elec-
329 tronsandionsfromthesolarwindandcosmicrays[82–86]andbecomephoto-or
330 pressure-polymerized[87,88] in the harsh environment of the lunar regolith.
331 Fullerenemultimers,becauseoftheirverylowsolubilitiesinorganicsolvents,
332 areveryhardtodetect.Anadditionallossmechanismfromtheequatorialregion
333 oftheMoonisduetotheestimatedrelativelyshortstickingtimeof270sofC60
334 at the very top of the regolith of the two landing sites. That time rapidly
335 lengthens towards the cooler lunar Poles, which means that fullerenes could
336 have slowly migrated north- and southward away from the more equatorial
Terrestrialand Extraterrestrial Fullerenes 341
337 Apollo sampling areas.[89] The diffusional migration can also proceed down-
338 wardintotheregolithbecausethepenetrationofthediurnallunarheatwaveis
339 veryshallow.ThatwasthereasonwhytheApollo17samplewasstudied.
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3.3. Terrestrial Rocks, Overview
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Fullereneshavebeenreportedintwodistinctlydifferentkindsofterrestrial
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rocks:hard,carbon-richformationsandsediments.Thehardmaterialsoccurin
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the so-called shungite formation of Karelia, Russia, in the large-body impact
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structureatSudbury,Ontario,Canada,andinbitumensamongpillow-lavasof
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the Bohemian massif, Czech Republic, and Coals of the Yunnan province of
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thePeople’sRepublicofChina.Thesematerialsmayhaveincommonthattheir
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parent materials were biological remains. The sedimentary rocks come from
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formations at the Creataceous-Tertiary Boundary (KTB) and the Permo-
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Triassic Boundary (PTB). These formations are associated with catastrophic
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massextinctionsofspecies.Figure1ashowsthelocationsoffullerenesinhard F1
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rocks. Figure 1b shows the locations of fullerenes in sedimentary rocks.
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356 3.4. Hard Rocks
357
358 3.4.1. Shungite
359
360 We received valuable guidance and information for the writing of this
361 section from an unpublished manuscript by Dr. Buseck. Buseck et al.[90]
362 reported the serendipitous finding of C60 by high-resolution transmission
363 electron microscopy in shungite, a metamorphosed carbon-rich rock within
364 Precambriansedimentsofabout1.8GyontheKolaPeninsulaofRussia.They
365 followedthroughbyanalyzingpowderedsampleswithLaserDesorptionMass
366 Spectrometry(LDMS),whichconfirmedthepresenceofthefullerene.[91,92]A
367 number of subsequent studies have also found small concentrations of C60 in
368 shungite.[93–101] Other investigators have questioned these reports or have
369 failed to find fullerenes in their samples of shungite.[102,103]
370 ThepresenceofC60inshungiteisenigmatic.Thereisnoevidenceforany
371 high-energyeventsatShungasuchasameteoriteimpactstructureorlightning
372 strikes.[104,105] Because the age of the Karelian shungite could be closely the
373 same as that of the Sudbury impact structure (see below) it seems marginally
374 possible that the shungite C60 is due to a world-wide fullerene-bearing dust
375 depositfromtheSudburyevent.If,however,theformationwaslocalorinsitu,
376 then one must try to understand the origin of the C60 in the context of the
377 origin and formation of the carbon itself. The principal sources for the
378 shungite can be either biogenic or volcanogenic.[106] It is not yet known
342 Heymannet al.
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Figure 1. (a) World map showing the locations where fullerenes were reportedly
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found in hard rocks. 1¼Shunga, Karelia, Russia. 2¼Sudbury, Ontario, Canada.
411 3¼Mitov, Czech Republic. 4¼Yunnan Province, Peoples Republic of China.
412 (b) World map showing the locations where fullerenes were searched in soft rocks.
413 1¼WoodsideCreek,NewZealand.2¼FlaxbourneRiver,NewZealand.3¼Caravaca,
414 Spain. 4¼Sumbar, Turkmenistan. 5¼Stevns Klint, Denmark. 6¼Elendgraben,
415 Austria. 7¼Tetri Tskaro, Georgia. 8¼Brazos River, Texas, USA. 9¼Gubbio, Italy.
416 10¼RatonBasin(BocaRaton),Colorado,USA;11¼Sasayama,Japan.12¼Meishan,
PeoplesRepublicofChina.13¼Ba´lva´ny,Hungary.
417 POORQUALITY
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