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Olivine composition in chondrites
Geochimicaet CosmochimksActa, 1963,Vol. 27,pp. 1011to 1023. PergamonPressLtd. Printedin NorthernIreland
Ofivine composition in chondrites BRIAN The American
MASON
Museum of Natural History, New York, U.S.A.
Ah&&&--Olivine is almost omnipresent in chondrites, being absent only in the enstatite chondrites and a few carbonaceous chondrites. In most chondrites it is the dominant mineral. Since it shows a considerable range of composition, which is directly related to the FeO/MgO ratio in the individual meteorite, and since its composition is readily determined either by X-ray diffraction or by refractive index measurement, its composition provides an excellent criterion for the class~~ation of chondrites. This paper reports the ohvine composition in about 800 of the approximately one thousand chondrites known; of the ehondritcs examined, 14 are enstatite chondrites, 364 are olivine-bronzite chondrites, 427 are ohvine-hypersthene chondrites, 12 are olivine-pigeonite chondrites, and 17 are carbonaceous chondrites. The significance of these data for theories of the origin of chondrites is briefly discussed, and it is suggested that the different types of chondrites may represent samples from different regions of the pre-planetary solar system. INTRODUCTION
paper (MASON, 1962) I discussed the classification of chondritic meteorites. PRIOR’S subdivision (1920) into enstatite, olivine-bronzite, and olivinehypersthene ohondrites was extended by the addition of two groups, the olivinepigeon&e and the carbonaceous ehondrites. It was pointed out that in spite of the use of miIleralogica1 terms to describe the individual groups, PRIOR’s classi~cation was based on chemical criteria. PRIOR himself used the MgO/FeO ratio in the bulk analysis, making the division at the bronzite boundaries of MgO/FeO 9 and 4 (corresponding to 10 mole percent FeSiO, and 20 mole percent FeSiO, in the orthopyroxene). The application of PRIOR’S classification in this form leads to serious difficulties-it cannot be applied to the numerous chondrites which have not been analysed; analyses of weathered chondrites are misleading, because the MgO/FeO ratio has been modified by terrestrial oxidation of the nickel-iron; and Fe0 in chondritic meteorites is notoriously difficult to determine accurately, many of the reported results being demonstrably wrong (UREY and CRAIG, 1953). I therefore suggested that PRIOR’S classification be based on the actual composition of the minerals present, rather than a oal~~ated composition based on chemical analysis, and proposed the use of olivine as the significant mineral. Olivine was proposed because it is the dominant mineral in most of the chondritic meteorites, and is present in all of them except the enstatite chondrites and some of the carbonaceous chondrites. Olivine has the advantage over pyroxene that it is essentially a binary solid solution of Mg,SiO, and Fe,SiO,, and its composition in terms of these components is readily determined by physical methods, measurement of refractive index or the position of selected reflections in an X-ray diffraction pattern being recommended. Since that paper I have procured samples of as many chondrites as possible and measured their olivine composition, by the X-ray diffraction procedure developed IN A recent
1011
1012
BRIANMASON
by Y~DER and S~HAMA (1957), and usually also by the measurement of the gamma refractive index in a crushed fragment of the meteorite. The latter procedure is rapid and requires comparatively simple and inexpensive equipment (a polarizing microscope and a set of calibrated refractive index oils): the gamma index is most readily measured because it is easy to select highly birefringent olivine grains from However, the X-ray method is probably more precise admixed ortho-pyroxene. and accurate, and the form of the diffractometer trace of the olivine reflections shows immediately if the olivine is of uniform composition (as is normally the case) or if it has a range of composition (as in most of the olivine-pigeonite chondrites). The diffractometer procedure was calibrated by the use of standard olivines of known composition kindly provided by H. S. YODER from the material used by T. G. SAHAMA and himself in their original work. The same diffractometer was used under the same conditions throughout this work, and the standards were re-run occasionally to check on the stability of operation. Control measurements and repeated measurements of some specimens at different times indicate that the precision and accuracy of the figures for Fa content (mole percent Fe,SiO,) are & 1 percent. A large number of the meteorites studied came from the collection of the However, I have endeavoured to make American Museum of Natural History. this survey as comprehensive as possible, and have been greatly aided by additional material from many sources. It is hardly feasible to acknowledge all these sources, but I am especially indebted to the U.S. National Museum, the Nininger Meteorite Collection (Arizona State University), the British Museum (Natural History), the Museum National d’Histoire Naturelle (Paris), and the Committee on Meteorites of the Academy of Sciences of the U.S.S.R. The data on olivine composition will be presented in reference to the five groups Of some one thousand chondrites so far of chondrites previously established. recognized, about 950 are either olivine-bronzite or olivine-hypersthene chondrites, and the data for these are correspondingly voluminous. The names of the meteorites are those used in the PRIOR-HEY catalog (1953) or the supplement published by KEIL (1961), and further information regarding the individual meteorites will be found in these sources. Meteorites not listed in either of these sources are briefly described in the appendix to this paper. THE ENSTATITE CHONDRITES Olivine appears to be absent from the enstatite chondrites; most, if not all, of them contain excess silica in the form of tridymite and/or quartz, and at these compositions olivine cannot coexist in stable equilibrium. The orthopyroxene in these meteorites is essentially pure MgSiO,, the iron being confined to the metal and sulphide phases. In an enstatite chondrite with a deficiency of silica olivine could occur; its composition would be forsterite, pure Mg,SiO,. THE CARBONACEOUSCHOWDRITES The carbonaceous chondrites were divided by WIIK (1956) into three groups, on the basis of their chemical analyses. He referred to these groups as Type I, Type II, and Type III, and this division will be utilized here, since the chemical.
Olivine
composition
1013
in ohond&es
composition and the mineralogical composition are directly related. The Type III carbonaceous chondrites belong to the oliviiie-pigeonite chondrites and are included therein, The Type I carbonaceous chondrites (Alais, Ivuna, Orgueil, and Tonk) contain no olivine. In the Type II carbonaceous chondrites (Alais, Bells, Boriskino, Cold Bokkeveld, Cresent, Erakot, Haripura, Mighei, Murray, Nawapali, Nogoya, and Santa Cruz) olivine is a minor constituent, usually comprising in the form of small scattered grains and 10-30 percent of the meteorite, chondrules. Usually this oliviue gives sharp peaks ou a diffractometer trsee, and is almost pure ~~g~SiO~, with less than 5 percent Fe&O, in solid solution, but in some of these meteorites (e.g. Haripura) it is variable in composit,ioll, with a predominance of forsteritic olivine but with some material ranging up to a Renazzo, a unique carbonaceous content of about 30 mole percent Fe&O,. chondrite differing from all others in containing a col~siderable amount (about 11 percent) of nickel-iron, has olivine close to Mg,SiO, in composition (Mason and ~ITK, 1962). Tm
OLIVINE-PIGI~ONITEC'H~FJDBITES
Most of the olivine-pigeonite chondrites, in contrast to practically all other chondritie meteorites, eonta,in olivine showing a wide rauge of compositioll, from Fa, (pure ~lg~~iO*) to Fa,,_,,. These include the Type III carbol~aceous ~hondrites~ Table 1. Olivine cor~~~osition in the olivinepigeonite chondrites (an asterisk indicates a carbonaceous chondrito) *Bali Felix *Qrosnaja *Kaba Karoonda Lance *Xokoia Xgawi Ornans Tieschitz *Vigarano ~~arrento~
O-60 20-60 O-65 O-65 33 10-50 O-65 30 25-60 104% O-60 25-55
which however do not differ essentially in chemical and mineralogical oomposition from the non-carbonaceous olivine-pigeonite chondrites. In those meteorites with variable olivine composition, the mean composition of the olivine is near FaQB, the same as in the other chondrites of this group. The data are given in Table 1. THE OLIVI~E-BR~~ZITE AND O~~V~~E-~YP~~~~H~~E
~H~~~R~T~s
These two groups comprise over 90 percent of all chandrites, and are approximately equal in abundance. The olivine compositions of individual meteorites of these two groups are given in Table 2. 3
BRIAN MASON
1014 Table
composition in olivine-bronzite and olivine-hypersthene chondrites, in mole chondrites, olivine~bro~ite chondrites, Fe~,,_~r, olivine-hypersthene FezSiOo (Fa); (Those meteorites not recorded in the PRIOR-HEY catalog (1953) or by KEIL (1960) Fass-s,. are printed in italics and are briefly described in the Appendix. An asterisk indicates an observed fall). per
2. Olivine
cent
*Aarhus, 18; Abernathy, 23; Abe, 19; Adams County, 19; Adelie Land, 19; Akron, *Akaba, 24; *Akbarpur, 27; Albin, Alamosa, 25; *Albareto, *Alexandrovsky, 18; *Alfianello, 24; herst, 25, *Andover, 25; *Angers, 25; 23; Arcadia, 29; *Archie, 20; Arriba, *Ashdon, 25; Assam, 24; *Ass&, 19; *Aumale, 25; *Aumieres, 24; Aurora,
19; Accdana, 24; Achilles, 20; *Achiras, 25; Acme, 24; Adrian, 19; *Agen, 20; *Aguada, 25; *Air, 23; 19; Akron No. 2, 16; *Akwanga., 19; Alamogordo, 19; 22; *Aldsworth, 28; *Aleppo, 24; *Alessandria, 18; Nagla, 19; Amber, 24; Am*Allegan, 19; *Ambapur Anthony, 19; *Appley Bridge, 29; *Apt, 24; Arapahoe, 25; Artracoona, 24; *Asco, 26; Ashburton Downs, 24; *Atarra, 23; *Atemajac, 23; *Athens, 31; *Atoka, 24; 19; *Ausson, 25; *Avilez, 19; *Aztec, 24.
25; *Bandong, 28; *Banswwl, 24; *Bar*Bachmut, 24; *Bald Mountain, 24; *Baldwyn, botan, 24; *Baroti, 25; Barratta, 25; *Bath, 19, *Bath Furnace, 24; *Baxter, 24; *Beardsley, 19; Beenham, 23; BeZZe Plaine, 24; Belly River, 20; 20; *Beaver Creek, 19; *Beddgelert, *Benares, 28; *Benld, 20; *Benton, 31; Berdyansk, 25; *Berlanguillas, 25; *Bethlehem, 19; 26; *Bhagur, 25; *Bherai, 24; *Bhola, 27; *Bielokrynitschie, 20; *Beuste, 25; *Beyrout, *Birni N’konni, 18; *Bishunpur, 18; *Bjelaja Zerkov, 20; *Bjurbole, 26; *Black Moshannan Park, 24; *Blanket, 24, *Blansko, 19; Bluff, 25; *Boeas, 26; Boelus. 30; Boerne, 20; Bogoslovka, 19; Bolshaya Korta, 19; Bonita Springs, 20; *Borgo San Donino, 29; *Bori, 25; *Borkut, 26; *Borodino, 20; *Botschetschki, 26; Bowden, 18; Brady, 25, *Breitscheid, 19: *Bremervorde, 24; Brewster, 24; Briscoe, 26; Broken Bow, 20; Brownfield, 19; *13rutierheim., 24;
*Bur-Gheluai,
19; *Buschhof,
24; Bushnell,
19; *Butsura,
19.
*Cabezo de Mayo, 24; &dell, 24; ~~~l~~rn, 23; *Canellas, 17; *Cangas de Onis, 18; *Cape Girardcau , 19 ; *Caratash, 29, Carcote, 20; Caroline, 19; Carraweena, 24; C’art,oonkana., 24; Cashion, 18, *Castalia, 19; *Castine, 25; Cavour, 19; Cedar (Kansas), 18; Cedar (Texas), 18; *Coreseto, 19; *Chail, 18; Chamberlin, 18; *Chandakapur, 24; *Chandpur, 23; Channing, 19; *Chantonnay, 23; *Charsonville, 18; *Charwallas, 19; *Chateau-Renard, 25; *Cherokee 26; Chico, 27; *Chicora, 29; Clareton, 25; *Clohars, 25; Clovis, Springs, 28; *Chervettaz, 19; Cobija, 19; Cocunda, 24; Colby (Kansas), 18; *Colby (Wisconsin), 25; Coldwater, 17; *~ollesc~poli, 19; Concho, 23; Coolidge, 14; ~oomandook, 19; Coon Bmte, 24; Cope, 18; &&&a, 19; Cortcz, 19; *Cosina, 19; Cotesfield, 23; Cott~~~oo~, 18; Covert, 18; Y’ranganore, 24; *Cronstad, 18; Crosbyton, 17; *Cross Roads, 18; *Crumlin, 24; Cuero, 19; Culbert’son, 18; Cullison, 18; Cushing, 19; *Cynthiana, 25. DaEe Dry Lake, 24; ‘Dandapur, 25; *Danvillo, 23; Daoura, 23; *Darmstadt,, 19; Davy, 23; *Deal, 25; Death liulley, 20; *De Cewsville, 18; *Demina, 23; De Nova, 23; Densmore, 23; *Dhurmsala, 26; *Diep River, 25; ~~~.boola, 19; Dimmitt, 20; ~~~~~~c~, 18; Dix, 23; *DjatiPengilon, 20; *l&rmaia, 19; *Dokachi, 19; *Dolgovoli, 25; “Romanitch, 24; *Donga Kohrod 19; *Doroninsk, 19; *Dowo, 25; *Douar Mghila, 30; Doyleville, 20; *Drake Creek, 25; *Dresden, 20; DuncanviZZe, 19; *Dundrum, 19; *Durala, 25; *Duruma, 25; Dwight, 25. *Ehole, 19; *Eichstadt, 20; *Ekeby, 19; *Elenovka, 25; Eli Elwah, 23; Elkhart, 18; Ellerslie, 25; Elm Creek, 18; El Perdido, 19; Elsinora, 17; *Ensisheim, 28, *Epinal, 19; *Ergheo, 25; Erofeevka, 17; *Erxleben, 19; *Esnandes, 18; Estaeado, 19; *Eszc, 19; Eustis, 18. 18 ; *Farmington, 24; *Farmville, 18; Farnum, 25; *Favars, 18; *Payetteville, Chair, 17; *FBnghsien-ku, 18; Ferguson Switch, 1’7; *Fisher, 23; Fleming, 18; *Florence, 17; Forestburg, 24; *Forest City, 19; *Forest Vale, 17; *Forksville, 26; *Forsbach, 19; *Forsyth, 23; Franklin, 19; *Fukutomi, 24; *Futtehpur, 24. 19;
Farley, *Feid
Olivine Gail, 18; *Galapian, 19; Gerona, 19; *Gifu,
composition
1015
in chondrites
20; *Galim, 29; *Gambat, 23; Garnet& 20; Garraf, 24; *G&darn, 25; Gilgoin, 17; *Girgenti, 25; *Git-Git, 24; Gladstone, 17; *Glas-
atovo, 18; *Gnadenfrei, 18, Gnubara, 19; Goodland, 25; *Gopalpur, 20, Grady (1933), 25; Grady (1937), 15; Grant County, 26; *Great Bear Lake, 19; Gretna, 25; *Gross-Divina, 19; *Grossliebenthal, 25; *Grimeberg, 17; Gruver, 19; Gualeguaychu, 19; *Guarena, 19; *Guidder, 29; *Gumoschnik, 19; *Gurram Konda, 24; *Giitersloh, 20. *Hainaut, 19; Hale Center (No. l), 25; Hale Center (No. 2), 17; *Hallingeberg, 25; *HamI&, 27; Harding County, 26; Hardwick, 24; *HurZeton, 26; *Harrison County, 26; Harrisonville, 24; Haskell, 23; ~~~~ayu~~~, 18; Hat Creek, 18; Haven, 20; Haviland, 19; Hawk 24; Hendersonville, 24; *Heredia, Springs, 19; Hayes Center, 23; *Hedeskoga, 19; *Hedjaz, 18; Hermitage Plains, 24; *He&e, 19; Hesston, 24; *Higashi-koen, 19; *High Possil, 25; Hildreth, 25; Hinojo, 20; Hobbs, 19; *Hokmark, 24; *Holbrook, 25; Holly, 18, *Holman Island, 29; Holyoke, 19; *Homestead, 24; *Honolulu, 24; Horace (No. I), 19; Horace (No. 2), 25; Howe, 19; Hugo, 17; Hugoton, 16; *Hungen, 19. 19; Imperial, *Iehkala, 18; *Idutywa, Ioka, 23; *1&ingu, 18; Isoulane-n-Amahar,
18; Indianola, 25; *Isthilart,
24; Indio Rico, 18; 18; *Itapicuru-Mirim,
Ingalls, 18.
*Jackalsfontein, 24; *Jamkheir, 19; *Jelica, 31; *Jemlapur, 25; Jerome (Idaho), Jerome (Kansas), 19; *Jhung, 25; Johnson City, 25; Juarez, 24; *Judesegeri, 18; Junction,
20;
24; 24.
*Kadonah, 17; *Kaee, 19; QKagarlyk, 23; *Kakowa, 23; Ka~d~oner~ Hill, 19; *Kalumbi, 24; *Kamsagar, 24; *Kcmdczhur (Afghanistan), 24; *Kangra Valley, 19; Kansas City, 19; Kappakoola, 17; *Kaptal-Aryk, 23; Karagai, 23; *Karakol, 28; *Karewar, 24; *KcrZuwaZa, 23, *Karkh, 25; Karval, 19; Kaufman, 23; Kearney, 20; Kelly, 29; *Kendleton, 25; *Kerilis, 19; Kermichel, 24; *Kernouve, 18; *Kesen, 17; Keyes, 23; *Khanpur, 29; *Kharkov, 24; *Kheragur, 24, *Khetri, 18; *Khmelevka, 23; *Khohar, 23; *Kikino, 19; *Kilbourn, 19; *Killeter, 20; Kimble County, 19; Kingfisher ,23; Kingoonya, 24; Kissij, 17; *Klein-Wenden, 19; *Knyahinya, 25; Koraleigh, 24; Wrahenberg, 27; *Krasnoi.Ugol, 24; *Krymka, 18; *Kukschin, 24; *Kuleschovka, 25; K&nine, 24; *Kunashak, 24, *Kusiali, 24; *Kuttippuram, 25; *Kuznetzovo, 23; *Kyushu, 26. *La Becasse, 23; *Laborel, 19; *La Colina, 17; Ladder Creek, 25; *L’Aigle, 23; Lake Brown, 25; Lake Labyrinth, 28, Lake Moore, 25; Laketon, 25; La Lande, 24; *Lalitpur, 24; *Lancon, 19; *LZmghalsen, 26; *Launton, 23; La Villa, 19; *Lavrentievka, 24; Lawrence, 23; *Leedey, 24; *Leeuwfontein, 24; *Leighton, 20; *Leonovka, 24; *Le Pressoir, 24; *Les Ormes, 24; *Leaves, 25; *LilIaverke, 18; *Limerick, 19; Lincoln County, 24; *Linum, 23; *Lissa, 23; *Little Piney, 23; *Lixna, 20; Lockney, 23; Logan, 19; Long Island, 25; Loomis, 23; Lost Lake, 25; Loyola, 23; (the Loyola meteorite appears to be a stone from the Homestead fall). *Lua, 24; Lubbock, 24; *Lute, 24; *Lumpkin, 19; Lundsgbrd, 24; *Luponnas, 19; Lutschaunig’s St,one, 24. *Macau, 19; *Madrid, 24; Maim, 25; Makmewa, 24; *Malampaka, 19; *MaIotas, 19; *Mamra Springs, 24; ‘Manbhoom, 30; *Mangwendi, 29; *I%~ardn.~, 19; *Marion (Iowa), 24; _!arion (Kansas), 24; Marlow, 24; *Marmande, 24; Marsland, 16; *Mascombes, 24; *Mauerkirchen, 24; *Mauritius, 26; Mayday, 19; *Maziba, 25; McAdoo, 25; McKinney, 24; McLean, 19; Mellenbye, 27; Melrose, 23; *Menow, 18; *Meridi, 19; *Mern, 24; *Meru, 28; *Merua; 18; Mets@&, 18, *Meuselbach, 24; *Mezel, 24; *Mezo-Madaras, 26; *Mhow, 24; Miami, 17, *Middlesbrough, 23; *Mike, 24; *Milena, 24; *Miller (Arkansas), 19; Miller (Kansas), 19; kfinas Gerais, 25; *kfirzapur, 24; *Misshof, 19; Mission, 23: *Mjelleim, 19; *Moos, 24; *Modoc (lBO5), 23; Modoc (1948),22; *Molina, 24; *Monroe, 19; *Monte das Fortes, 24; *Monte Milone, 25; *Montlivault, 24; *Monze, 25; *Mooresfort, 19; *Moorleah, 23; *Moradabad, 24; Morland, 19; *Mornans, 19; Morven, 18; *Moti-ka-nagla, 19; *Motta di Conti, 17; Mount Morris (New York), 17; *Muddoor, 19; Muizenberg, 24; *Mullctiwu, 25; Muroc, 25; Muroc Dry Lake, 25.
BRIAN MASOJS
1016
24; *~ammiant.hal, 19; Wanjemoy, 18; *Kan Yang *~adiabondi, 18; Wagy-Borove, P&O, 24; *il’aoki, 20; Nardoo, 25 (one of the two st,ones, the other being identical with Elsinora): 19; Nazareth, 19; Neenach, 24; *Narellan 28; Naruna, 19; il’iis, 30; Nashville, 22; Wassirah, *Nerft, 23; Xess County (1894), 25; Ness County (1938), 20; New Almelo, 24; *Kew Concord, 24; Sowsom, 24; *Xkolaevkx, 19; *Nikolskoje, 24; Xorcateur, 25; *R’opan-Bogdo, 24; *Sulles, 19.
19: 30; 14;
Oakley, 21; Oberlin, 27; *Ochansk, 20; Oezeretna., 19; *&set, 25; *O-Fehert,o, 23; *Ogi, 24; Okirai, 19; *Okniny, 27; *Olivenza, *Ohaba, 20; *Ojuelos Altos, 25; Okechobee, *Olmedilla de Alarcon, 18; Orlovka, 19; *Orvinio, 23; Oshkosh, 18; *Oterwy, 25; Otis, *Ot,tawa, 29; *Oua,llen, 20; Oobari, 26; Ovid, 20; *Oviedo, 25; Ozona , 19 .
*P&c&,, 24; Pampa de Agua Blanca, 24; Pampa de1 Infierno, 24; *Pampanga, 24; *Pantar, 26; *Patrimo&o, 25; *Pavlograd, 25; Peck’s Spring, 25; 25; *Par&lee, 18; *Paragoultl, P&z, 26; Penokee, 19; *Perpeti, 25; *Perth, 28; *Per~o~na~sky, 24; Petropavlovka, 16; 24; Pinto Pevensry, 28; *Phu-Hong, 18; *Phum Sambo, 19; Pickens County, 20; Piercevillc, 18; Plainview (1917), 19; Pfainview Xountains, 24; Pipe Creek, 19; *Pirgunje, 28; *Pirthalla, (1950), %O; *Plant,ers~~ille, 20; Pleasanton, 18; *Ploschkovitz, 24; *~nompehll, 24; *Pohlitz, ‘t 5; *Pokhra., 18; Potter, 23; Prairie Dog Creek. 19; *Pribram, 20; *Pricetown, 24; Pllente18. Ladron, 24; *l?ulsora, 19; *Pultusk, *Queens
Ncrcy,
18;
‘Qrtenggouk,
19;
*&uincay,
24;
*R&co, 18; *R.akovka; 24; *Ramsdorf, 25; *Ranchapur, 19; *Ranch0 de la Press, 19; *Rangala, 25; .Ransom, 19; ~~~~~~~~,a, 20; Reager, 25; ‘Reliegos, 23; *Renca, 24; *Richardt,on, 19; *Richmond, 26; *Rich Mountain, 24; *Rio Negro, 25; *Rochester, 20; Rolla, IQ; ( W. H. Nininger has recognized five different; Rolla meteorites, but t)hey are all olivine-bronzite chondrites of similar composition, and are here treat,ed as a singlo find). Romero, 19; Rosamond Dry Lake, 24; Rosebud. 19; *Rose City, 19; Roy (1933), 25; Roy (1934), 24; Rush County, 17; Rush Creek, 26; Rushville, 24; *Ryochki, 23. St. Ann, 18; *St. Caprais-~le.~uinsac, 25; *St. Christ,oph~-la-Cha~,r~?use, 25; *St. DenisWestrom, 25; *St. Germ&in-du-Pin& 18; *hk Louis, 19; *c%. Marguerite, 20; *St. Mesmin, 29; *St. Michel, 24; St. Peter, 25; Salino, 18; *Salles, 18; Salt Lake City, 19; San Carlos, 18; San Emigdio, 20; San Joso, 18; San Pedro Springs, 23; *Santa Barbara, 25; *Santa Isabel, 24; *Saratoy, 24; *Sauguis, 25; *Savtschenskoje, 28; Schaap-Kooi, 19; *Schollin, 26; *Schonenberg, 25; Scott City, 20; J’cww~, 19; *Searsmont, 19; *Segowlie, 25; Seg&n, 20; Heibert, 18; *Scldebonrak, 19; Selma, 20; *Semarkona, 20; *Sena, 17; Seneca, 19; *Seres, 17; *S&e Lagoas, 19; *Xevilla, 28; *Sevrukovo, 25; Shafter Lake, 19; *Sharps, 28; Shaw 23, *Shelburne, 24; *Shupiyan, 19; *Shytal, 25; ,SWney, 24; *Siena, 28; Silverton (Now Sduth Wales), 25; Silverton, (Texas), 17; *Simmcrn, 19; *Sinai, 23; *Sindhri, 19; *Sitathali, 19; *Ski, 24; *Slavetic, IT; *Slobodka, 23; Smith Center, 24; *Soko-Banja, 27; Springfield, 23; *Stalldalen , 19 ; “Stavropol, 24, Sto~ington, 19; *Strathmore, 25; ~~.~~~e~te,24, *Success, 24; *Sultanpur, 26; *Supuhee, 19; Suwahib-Adraj, 23; Suwa,hib-Ain Rala, 18; Suwahib-Buwah, 14; *Sylaeauga, 20. *Tabor, 18; *Tadjera, 25; Taiban, 25; Taiga, 19, “Takenouchi, 19; *Tan&, 25; Tarbagatai, 23; Tqfa, 25; Tatum, 18; *Tauq, 25; Tern&, 25; *Tenham, 24; *Tennasilm, 23; Texline, 19; *ThaZ, 19; Thomson, 24; *Tildon, 26; *Timochin, 20; *Tirupati, 18; *Tjabe, 19; *Tjerebon, 24; *Tomakovka, 30; *Tomattan, 18; Tomhannock Creek, 18; *Torrington, 18; Tostado, 19; *Toulouse, 19; *Tourinnes-la-Grosse, 25; Travis County, 18; *Trenzano, 19; *Tromq, 18; *Troup, 28; Tryon, 24; *Trysil, 25; *Tuan Tut, 24; Tuba, 20; Tuzla, 25; T~e~~~~~n~ Patnzs, 26; *Tysnes Island, 20. *Uberaba, 19; *Uden, 30; *Udipi, 18; Ultuna, 18; Ulysses, 17; *Umbala, 23; Ute Creek, 19; *Utrecht, 24; *Utzenstorf, 18; Uvalde, 19.
28; UmmTina,
Olivine composition in chondrites
1017
*Vago, 19; *\‘aldavur, 20; *\Ta~ldinizza,24; Valkeala, 24; Valley IVells, 24; \?arpaisjarvi, 25; *Vax*ilovka 7 30.f *\Tengerovo, 19; Vera, 24; *Verkhne Tschirskaia, 18; *\‘ernon County, 19; Villedieu, 19; l’incent, 24; *Virba, 25; *Vishnupur, 30; *Vouihe, 24. Kaconda, 25; Wairarapa TTalby, 18; Waldo, 25; *Walters, 25; JVeldona, 19; Wellman, 18; *wesso1y, 18; *Weston, 19; Whitman, 19; Wickenburg, 23; IVilburton, 25; W~illowdale, 20; lV:ilmot, 18; 1Pi~ngelZilza,19; *Wit,klip Farm, 18; *Wit,sand Farm, 27; *\f%t,ckrantz, 23; *IVotd Cott,agc, 24; Woodward Coumy, 19; Wray, 15. Yandama, 25; *Vatoor, 19; *Yonoeu, 18; York, 24; ~Y~r~tou~~~,24; (A.M.K.H. specimen; specimens from the British &Iuaeum and the Chicago Nat~wai History ?;LUS
The data are most readily comprehended in the form of diagra,nls (Fig. 1). ‘I’hese show a remarkable qua,nt,ization in the olivine composition; most of the olivinebronzitJe chondrites have olivine with composition Far,_,,, most of the olivinehypersthene chondrites have olivine with composition Fa,,_,5. It is immediately apparent that, these two groups, instead of forming a co~~til~uous series as envisaged by PRIOR, are separated by a marked hiatus. This also corresponds to a significant difference in bulk composition; the olivine-hypersthene chondrites are uniformly lower in total iron (average about 21 percent)-the low-iron (L) group of UREV and CRAIG (1~~3)-thar~ are the oli~ine-bro~lzite cho~~drites (t,ttta,l Fe averages about 27 percent)---the high-iron (H) group of UREY and CRA’EG. The limits of olivine composition for the two groups are I%,,_.,, for the olivinebronzite chondrites and Pa,,_,, for the olivi~le-hypersth~~n~ chondrites. Actually, in view of the limits of precision of the ~neasurements, it is quite possible t,hat chondrites wit,h olivine of mean composition Fa,, and Fa,, are completely lacking. The boundary between the olivine-bronzite and the olivine-hypersthene chondrites is drawn between Fa,, and Fe,,. I propose that this definition replace the original de~llit,ion of Prior based on chemical analysis, since the olivine com~~osition is more readily and possibly more accurately determinable than the FeO/MgO ratio in the bulk composition of the meteorite. With this definition the composition of the orthopyro~elle in the olivine-bronzite chondrites will always correspond to the definit,io~ of bronzite used by PRIOR---an orthopyroxene containing 10 to 20 mole percent FeSiO,-since the FeO/iMgO ratio in the orthopyroxene of chondrites is uniformly lower than this ratio in the olivine. It is possible that the orthopyroxcne in some of the olivine-hypersthene chondrites may contain sightly less than 20 mole percent FeSiO,, but this should cause no confusion in classification if olivine composition is used as the criterion. The total range of olivine composition in these meteorites is Fa,,_,,. The upper limit (%‘a,,) is readiIy explicable, since in meteorites with olivine of this composition virtually all the available iron is combined in the ferromagnesian silicates, there being essentially no metallio iron present. The lower limit (Fa,,) presents a problem for which there is no ready explanation. There is no obvious reason why more highly reduced olivine-bronzite chondrites (i.e. those with more free iron and less iron combined in the silicates) should not exist. Nevertheless, there is a complete
BRIANMASON
1018
80 OIlvine-bronzlte 70
60 g E
-
50
-
40 30 20
E B u
_~
10
E” ‘0 II
100
E z”
90
__
80
-
70
-
60
-
50
_
40
_
30
-
kz d
20
-
_..
10 -
10
15
20
25
30
35
Fig. 1. Distribution of olivine composition in olivine-bronzite olivine-hypersthene chondrites.
and
hiatus between the olivine-bronzite chondrites and the enstatite chondrites (in which all or practically a,11the iron is in the reduced state, and none or very little is present in the silicates). The numbers of meteorites in each of the two groups is given in Table 3. Considering the data for observed falls, of the 466 total, 196, or 42%, are olivinebronzite chondrites, 270, or 58’$&, are olivil~e-hypersthene chondrites. The numbers of each group are probably sufficiently large to justify the conclusion that olivinehypersthene chondrites have a somewhat greater absolute abundance than the olivine-bronzite chondrites. When we compare the relative numbers of finds versus observed falls in the two groups, we see that 53% of the olivine-bronzite chondrites are observed falls, compared to 64% of the olivine-hypersthene chondrites. In other words, oli~ine-bronzite chondrites occur more abundal~tly as finds than do the olivine-hypersthene chondrites. This is readily understandable in view of the general physical properties of the two groups; the olivine-bronzite chondrites contain much more nickel-iron (about 20%) than do the olivinehypersthene chondrites (about 8%). The nickel-iron tends to cement the silicate
Olivine composition in chondrites
1019
phases and give the meteorite a greater mechanical strength. In addition, the weathering of the nickel-iron causes an additional cementation through the chondrites are deposition of secondary iron oxides. Thus the o~vine-hypersthene probably much more rapidly broken down by weathering than are the olivinebronzite chondrites, and hence do not survive for so long periods on the Earth’s surface. It is no chance event that the majority of the finds of stony meteorites in the United StatSes have been tough limonitized olivine-bronzite chondrites. In view of the comparative large numbers of meteorites in each of these two groups, a study was made of dates and times of fall to see whether any statistically valid differences could be observed, either for hour of fall, day of fall, or month of fall. No marked differences were observed between the two groups. For each group the plot of hour of fall gave comparable curves, rising from a minimum in the early morning hours to a maximum between 3 p.m. and 5 p.m. and then falling Table
3. Numbers of olivine-bronzite and olivine-hypersthene chondrites enumerated in Table 2
Olivine-bronzite Olivine~hypersthene Totals
Falls 196 270
Finds 168 157
All 364 427
466
325
791
again. Analysis of the information for date of fall also shows a fairly regular distribution throughout the year, without any significant concentration of falls on specific dates; more have been observed to fall in the summer months than in the winter, but this is presumably a natural consequence of more favorable weather for observation and collection during the summer. Possibly a more searching analysis of the data, by narrowing the composition ranges and also taking into account the internal structure (degree of chondricity, etc.), might reveal some regularities of fall indicating a recurrence of specific meteorite types at regular inte~als. In view, however, of the extremely low percentage recovery (of the 500 meteorites estimated by Brtow~ (1961) to fall on the Earth each year the average recovery is between 4 and 8), the chance of discovering significant statistical informatiou from the analysis of data on observed falls cannot be great. DISCUSSION The data presented here clearly call for an explanation in any theory of the origin of the chondrites. PRIOR (1920) appreciated the marked overall chemical and mineralogical uniformity of the chondrites, and proposed that the different groups had been formed by the progressive oxidation of a highly reduced magma, t,he earliest stage being represented by the enstatite chondrites. Conversely, NASOH (1960) and RIMSWOOD (1961) have theorized that the parent material was highly oxidized, its original state being similar to that of the carbonaceous chondrites, the other groups of chondrites having been produced from this material by dehydration and progressive reduction. URSY and CRAIG (1953), from the occurrence of high-iron and low-iron chondrites, have argued that these types must have been
1020
BRIANMASON
derived from at least two asteroids of different composition. FISH, GOLES, and ANDERS (1960) have developed the theory that the different groups of chondrites (and the other meteorite types) were developed in bodies of asteroidal dimensions. RINGWOOD (1961) has presented a comprehensive theory for the origin of all meteorites within a single body of lunar or planetary dimensions. WOOD (1962) favors an origin of the different types of chondrites from different depths within a planetary body, the chondrules themselves having condensed as liquid droplets from cooling solar gases during the formation of the sun, and later aggregating into planets and asteroids. In my 1960 paper I wrote “Some of the facts regarding the chondrites are inconsistent with their origin either as massive fragments of a disrupted planet or The mineralogy of the typical caras aggregated dust from such a disruption. bonaceous chondrites.....shows that they have never been above 600” C and probably have always been at much lower temperatures. The texture and structure of the non-carbonaceous chondrites show that they are not fragments of a disrupted planet, for then gravitational segregation of silicate and metal should have taken place. Their mineralogy, especially the uniformity of composition of olivine and pyroxene in each individual meteorite, shows that they are not chance aggregates of dust but individual chemical systems in phase equilibrium. Their compositions are consistent with an origin by recrystallization of the material of carbonaceous chondrites. Such an origin does not require that they were ever part of a body or bodies of planetary or lunar dimensions, and their texture, their structure, and their mineralogy speak directly against such an origin”. It appears to me that the much more extensive data given in the present paper With some trepidation I venture in no way contradicts this earlier summation. to propose a theory for the origin of chondrites alternative to those outlined previously. Is it possible that the chondrites predate the formation of the larger bodies in the solar system! Are the different types of chondrites samples from different regions within a primordial dust cloud from which the planets aggregated! One can imagine this primordial dust cloud as a rotating lensoid body of gas and solid particles, varying in temperature, pressure, and composition from the center to the outer margin. The solid particles would tend to accumulate in an equat’orial zone. The temperature at the outer margin would be near absolute zero and would presumably increase towards the center, and the composition of the solid matter would change correspondingly, from frozen volatiles with little nonvolatile material near the margin to more refractory material towards the center. The discontinuities and hiatuses between the different chondrite groups may perhaps reflect incipient segregation and zonal aggregation within this equatorial band of solid particles. If we accept the logical succession from cold oxidized material at the outer margin to hotter and more reduced material towards the center, then this succession is represented among the chondrites by the sequence: carbonaceous chondrites (Type I)-carbonaceous chondrites (Type II)-olivinepigeonite chondrites-olivine-hypersthene chondrites-olivine-bronzite chondrites -enstatite chondrites. While this presents a broadly consistent picture, it is not obvious why the olivine-hypersthene chondrites contain 5 percent less total iron than chondrites in the other groups, nor why there should be a hiatus in the reduction
Olivine composition in chondrites
1021
sequence between the olivine-bro~zite chondrites and the enstatite chondrites. Perhaps the loss of iron from the material which formed the olivine-hypersthene chondrites was the result of its removal by a reaction which took place under rather specific conditions of temperature, pressure, and chemical environment (possibly The hiatus between the formation of a volatile iron compound such as a carbonyl). the olivine-bronzite chondrites and the enstatite chondrites may reflect an early segregation of the primordial dust cloud into different zones. In essence, therefore, I would suggest the possibility t,hat the chondrites represent sintered masses of pre-planetary material which in most insta,nces represent rlear-equilibrium for the temperature, pressure, and chemical environment The great preponderance of olivine-br0r~zit.e and olivinein which they formed. hypersthene chondrites can perhaps be ascribed to their representing the equilibrium conditions within large regions of the ancestral dust cloud and/or to their having originated within the general region of the terrestrial planets and the asteroidal belt. This concept that the chondrites have a pre-planetary origin is supported by recent work on their dating by the xenon method. BUTLER, JEFFEI~Y, REYNOLDS, and WASSERBCRG (1963) interpret the results of this work to indicate that the Earth post-dates the meteorites by about 200 million years. A~kno~~e(~gme~ts-The work reported in this paper has been supported (~~F~Gl4~47) from the Xational Science Foundation.
by a. research
grant
REFERENCES (1961) The density and mass distribution of meteorite bodies in t,hr neighbourhood of the Earth’s orbit. J. Geophys. Res. 68, 1316-1317. BUTLER IV. A., *JEFFREY P. M., REYNOLDS J. II. and WASSERBDR~ G. J. (1963) Isotopic variations in terrestrial xenon. J. Geophya‘. 12~. 68 (in press.) Frsa 12. A., GOLES G. G. and ANDERS E. (1960) The record in the meteorites. III. On the development of meteorites in asteroidal bodies. J. Astrophy. 132, 243-258. KEIL K. (1960) Fortschritte in der Meteoritcnkunde. Fortschr. Mineral. 38, 202-283. MASON B. (1960) The origin of meteorit,es. J. Ceophys. l&s. 65, 2965-2970. MASON B. (1962) The classification of the chondritic meteorites. A,mer. *~~~~~e~~rn _~~)~,~t~es 2085,20 pp. XARON R. and Wrrx H. 3. (1962) The Renazeo meteorite. Amer. ~~~z~se~~?n _~~~~~it~tes2106. I1 BROWN
R.
PP. PRIOR G, T. (1920) The classification of meteorites. Nin. Mug. 19, 51-63. PRIOR G. T. (1953) Catalogue cfl ~Weteorites. Second edition, revised by M. H. Hey, British Museum, London, 43.2 pp. RINGWOOD A. E. (1961) Chemical and genetic relationships among meteorites. G’eochim. et Cosmochim. Acta 24, 159-197. UREY H. C. and CRAIG H. (1953) The composition of the stone meteorites and the origin of the meteorites. Geochim. et Cosmochim. Actu 4, 36-82. WIIK H. B. (1956) The chemical aomposition of some stony meteorites. Geochim. et Cosmonhim. Acta 9, 279-289. WOOD J. A. (1962) Metanlorphis~~ in ohondrites. Ceochim. et Cosmochim. Acta 26, 739-750. YODF,R H. S. and SAHAMA T. C. (1957) Olivine X-ray determinat,ive curve. Amer. Mi?z. 42, 475-.491.
1022
Bmasr MASON APPENDIX
Meteorites mentioned in this paper which sre not recorded in the PRIOR-HEI’ catalog (1953) or by KEIL (1960).
Akron No. 2, Washington Caunty, Colorado; 40” 09’N, 103” 1O’W; found 1954; 0.64 kg. Akwanga, Nigeria; 8” 55’ N, 8” 26’ E; fell July 2, 1959; 3 kg. Ashburton Downs, Tniestern Australia; 23” 20’ S, 117” 06’ E; 1.8 kg. Belle Plaine, Sumner County, Kansas; 37” 19’ N, 97” 15’ W; found 1955; 24 kg. Bruderheim, Alberta, Canada; 53” 54’ N, 112” 53’ W; fell March 4, 1960; 300 kg. Calliham, McMullen County, Texas; 28” 25’ N, 98” 15’ W; found 1968; 40 kg. Clovis, Curry County New Mexico; 34” 18’ N. 103 08’ W; found 1961; 283 kg. Cocunda, Soubh Australia; 32” 49’ S, 134” 49’ E; found 1945-46; 0.5 kg. Coomandook, South Australia; 35” 25’ S, 139” 45’ E; found 1939; l*l kg. Cordoba,, Rio Negro, Argentina; 40” 09’ S, 68” 30’ W; fall? Cot*tonwood, Yavapai County, Arizona; 34” 50’ N, 112” 01’ W; found 1955; 0.8 kg. C’rosbyt,on, Crosby County, Texas; 33” 40’ N, 10X” 16’ W; find. Dale Dry Lake, San Bernardino County, California; 34” 02’ N, 115” 54’ W; found 1957; O-3 kg. Death Valley, Inyo County, California; 36” 21’ N, 116” 49’ W; found 1956. Dimboola, Victoria, Australia; 36” 30’ S, 142” 02’ E; found 1944; 16 kg. Dispatch, Smith County, Kansas; 39” 30’ N, 98” 32’ W; found 1956; O-22 kg. Djermaia, Chad, Africa; fell February 25, 1961; Dosso, Niger, Africa; 13” 03’ xi, 3” 10’ E; fell February 19, 1962; I.25 kg. Duncanvillc, Dallas County, Texas; 32” 38’ N, 96” 52’ W; found 1961; 17.8 kg, Whole, Angola, Africa; 17” 18’S, 15” 50’ E; fell Augusts 31, 1961; 2.4 kg. Esu, Sudan, Africa; fell March, 1941; 3.2 kg. Forestburg, Montague County, Texas; 33” 30’ N, 97” 39’W; found 1957; 26.6 kg. C+eidam, Nigeria; 13” N, 11” 52’ E; fell July 6, 1950; 0.72 kg. Namlett Starke County, Indiana; 41” 20’ N, 86” 35’ W; fell October 13, 1959; 2.95 kg. Hark&on, Harrison County, Texas; 32” 41’ N, 94” 31’ W; fell May 30,1961; 8.3 kg. IIassayampa, Maricopa County, Arizona; about 33” 45’ N, 112“ 40’ W; find; Hokmark, ~‘~sterbotten, Sweden; 64” 26’ N, 21” 13’ E; fell June 9, 1954; 0.30 kg. Ioka, Duchesne CYount,y,Utah; 40” 15’ N, 110’ 05’ W; found 1931; 31 kg. Ishinga, Tanganyika; 8” 56’ 8, 33” 48’ E; fell October 8, 1954; 0.13 kg. Jerome, Jerome County, Idaho; 42” 38’ N, 114” 50’ W; found 1954; 6.8 kg. Juarez, Buenos Aires province, Argentina; 37” 33’ 5, 60” 09’ W; found before 1938; Maldoonera :Flill, South Australia; 32” 30’ S, 134” 57’ E; found before 1956; 7 kg.
6.1 kg.
Kandahar, Afghanistan; 31” 36’ N, 65” 47’ E; fell November, 1959. Karluwala, West Pakistan; 31” 35’ N, 71” 36’ E: fell July 21, 1955, Lake Moore, Western Australia; 29” 51’ 5, 117” 33’ E; found before 1959; 13.6 kg. La Villa, Hidalgo County, Texas; 26” 16’ N, 97” 54’ W; found 1956; 19.8 kg. Mardan, West Pakistan; 34” 14’ N, 46” 46’ E; fell May 8, 1948. Marion, Marion County, Kansas; 38” 15’ K, 97’ 10’ W; found 1955; 2.89 kg. Mayday, Riley County, Kansas; 39” 28’ N, 96” 55’ W; found 1955; 6.9 kg. Metsakylb, Finland; 60” 39’ N, 27” 04’ E; found 1938; 1 kg. Oshkosh, Winnebago County, Wisconsin; 44” 02/N, 88” 33’W; found 1961; 0-I kg. Race, Tuouman province, Argentina; 26” 40’ S, 65” 27’ W; fell November 17, 1957; 5 kg. Rawlinna, Western Australia; 30” 22’S, 125“ 21’ E; found before 1959; 0.13 kg. Reager, Norton County, Kansa.s; 39” 47’ N, 100” 00’ W; found 1948; 0.23 kg. St. Louis, St. Louis County, Missouri; 38” 42’ N, 90” 14’ W; fell December 16, 1956; I kg. Scurry, Scurry County, Texas; 326” N, 101” W; found 1937; 115 kg. Seguin, Sheridan County, Kansas; 39” 22’ N, 100” 38’ W; found 1956; 6.75 kg. Sidney, Cheyenne County, Nebraska; 41” 03’ N, 102” 54’ W; found 1941; 6 kg. Sublette, Haskell County, Kansas; 37” 30’ N, 100” 50’ W; found 1952; 1.3 kg. Taiga; no information available (received from Dr. J. ZBhringer, Heidelberg). Tarfa, Saudi Arabia; 18’ 18’ h’, 58” 18’ E; found 1954.
Olivine
composition
in chondrites
10’3
Thal, West Pakistan; 33” 24’ N, 70” 36’ E; fell June, 1950. Temple, Bell Cormtg, Texas; 31” 07’ N, 97” 18’ W; found 1959; 0.2 kg. Twentynine Palms, San Bernardino County, Califo~ia; 34” 04’ N, 115’ 57’ W, found 1955; 19.6 kg. Valkeala, Finland; 61” 03’ N, 26” 50’ E; found May 1962; 0.4 kg. Vincent, South Australia; 36” 07’ S, 139” 53’ E; found before 1930; 0.4 kg. 37” 32’ N, 98” 22’ W; found 1951; 3 kg. Willowdale, Kingman County, Kansas; Wingellina, Western Australia; 26” 03’S, 128’ 57’ E; found 1958; 0.2 kg. Yorktown, West,chester County, New York; 41” 17’ X, 73” 49’ W; fell September 1869; 0.2 kg.
Ofivine composition in chondrites BRIAN The American
MASON
Museum of Natural History, New York, U.S.A.
Ah&&&--Olivine is almost omnipresent in chondrites, being absent only in the enstatite chondrites and a few carbonaceous chondrites. In most chondrites it is the dominant mineral. Since it shows a considerable range of composition, which is directly related to the FeO/MgO ratio in the individual meteorite, and since its composition is readily determined either by X-ray diffraction or by refractive index measurement, its composition provides an excellent criterion for the class~~ation of chondrites. This paper reports the ohvine composition in about 800 of the approximately one thousand chondrites known; of the ehondritcs examined, 14 are enstatite chondrites, 364 are olivine-bronzite chondrites, 427 are ohvine-hypersthene chondrites, 12 are olivine-pigeonite chondrites, and 17 are carbonaceous chondrites. The significance of these data for theories of the origin of chondrites is briefly discussed, and it is suggested that the different types of chondrites may represent samples from different regions of the pre-planetary solar system. INTRODUCTION
paper (MASON, 1962) I discussed the classification of chondritic meteorites. PRIOR’S subdivision (1920) into enstatite, olivine-bronzite, and olivinehypersthene ohondrites was extended by the addition of two groups, the olivinepigeon&e and the carbonaceous ehondrites. It was pointed out that in spite of the use of miIleralogica1 terms to describe the individual groups, PRIOR’s classi~cation was based on chemical criteria. PRIOR himself used the MgO/FeO ratio in the bulk analysis, making the division at the bronzite boundaries of MgO/FeO 9 and 4 (corresponding to 10 mole percent FeSiO, and 20 mole percent FeSiO, in the orthopyroxene). The application of PRIOR’S classification in this form leads to serious difficulties-it cannot be applied to the numerous chondrites which have not been analysed; analyses of weathered chondrites are misleading, because the MgO/FeO ratio has been modified by terrestrial oxidation of the nickel-iron; and Fe0 in chondritic meteorites is notoriously difficult to determine accurately, many of the reported results being demonstrably wrong (UREY and CRAIG, 1953). I therefore suggested that PRIOR’S classification be based on the actual composition of the minerals present, rather than a oal~~ated composition based on chemical analysis, and proposed the use of olivine as the significant mineral. Olivine was proposed because it is the dominant mineral in most of the chondritic meteorites, and is present in all of them except the enstatite chondrites and some of the carbonaceous chondrites. Olivine has the advantage over pyroxene that it is essentially a binary solid solution of Mg,SiO, and Fe,SiO,, and its composition in terms of these components is readily determined by physical methods, measurement of refractive index or the position of selected reflections in an X-ray diffraction pattern being recommended. Since that paper I have procured samples of as many chondrites as possible and measured their olivine composition, by the X-ray diffraction procedure developed IN A recent
1011
1012
BRIANMASON
by Y~DER and S~HAMA (1957), and usually also by the measurement of the gamma refractive index in a crushed fragment of the meteorite. The latter procedure is rapid and requires comparatively simple and inexpensive equipment (a polarizing microscope and a set of calibrated refractive index oils): the gamma index is most readily measured because it is easy to select highly birefringent olivine grains from However, the X-ray method is probably more precise admixed ortho-pyroxene. and accurate, and the form of the diffractometer trace of the olivine reflections shows immediately if the olivine is of uniform composition (as is normally the case) or if it has a range of composition (as in most of the olivine-pigeonite chondrites). The diffractometer procedure was calibrated by the use of standard olivines of known composition kindly provided by H. S. YODER from the material used by T. G. SAHAMA and himself in their original work. The same diffractometer was used under the same conditions throughout this work, and the standards were re-run occasionally to check on the stability of operation. Control measurements and repeated measurements of some specimens at different times indicate that the precision and accuracy of the figures for Fa content (mole percent Fe,SiO,) are & 1 percent. A large number of the meteorites studied came from the collection of the However, I have endeavoured to make American Museum of Natural History. this survey as comprehensive as possible, and have been greatly aided by additional material from many sources. It is hardly feasible to acknowledge all these sources, but I am especially indebted to the U.S. National Museum, the Nininger Meteorite Collection (Arizona State University), the British Museum (Natural History), the Museum National d’Histoire Naturelle (Paris), and the Committee on Meteorites of the Academy of Sciences of the U.S.S.R. The data on olivine composition will be presented in reference to the five groups Of some one thousand chondrites so far of chondrites previously established. recognized, about 950 are either olivine-bronzite or olivine-hypersthene chondrites, and the data for these are correspondingly voluminous. The names of the meteorites are those used in the PRIOR-HEY catalog (1953) or the supplement published by KEIL (1961), and further information regarding the individual meteorites will be found in these sources. Meteorites not listed in either of these sources are briefly described in the appendix to this paper. THE ENSTATITE CHONDRITES Olivine appears to be absent from the enstatite chondrites; most, if not all, of them contain excess silica in the form of tridymite and/or quartz, and at these compositions olivine cannot coexist in stable equilibrium. The orthopyroxene in these meteorites is essentially pure MgSiO,, the iron being confined to the metal and sulphide phases. In an enstatite chondrite with a deficiency of silica olivine could occur; its composition would be forsterite, pure Mg,SiO,. THE CARBONACEOUSCHOWDRITES The carbonaceous chondrites were divided by WIIK (1956) into three groups, on the basis of their chemical analyses. He referred to these groups as Type I, Type II, and Type III, and this division will be utilized here, since the chemical.
Olivine
composition
1013
in ohond&es
composition and the mineralogical composition are directly related. The Type III carbonaceous chondrites belong to the oliviiie-pigeonite chondrites and are included therein, The Type I carbonaceous chondrites (Alais, Ivuna, Orgueil, and Tonk) contain no olivine. In the Type II carbonaceous chondrites (Alais, Bells, Boriskino, Cold Bokkeveld, Cresent, Erakot, Haripura, Mighei, Murray, Nawapali, Nogoya, and Santa Cruz) olivine is a minor constituent, usually comprising in the form of small scattered grains and 10-30 percent of the meteorite, chondrules. Usually this oliviue gives sharp peaks ou a diffractometer trsee, and is almost pure ~~g~SiO~, with less than 5 percent Fe&O, in solid solution, but in some of these meteorites (e.g. Haripura) it is variable in composit,ioll, with a predominance of forsteritic olivine but with some material ranging up to a Renazzo, a unique carbonaceous content of about 30 mole percent Fe&O,. chondrite differing from all others in containing a col~siderable amount (about 11 percent) of nickel-iron, has olivine close to Mg,SiO, in composition (Mason and ~ITK, 1962). Tm
OLIVINE-PIGI~ONITEC'H~FJDBITES
Most of the olivine-pigeonite chondrites, in contrast to practically all other chondritie meteorites, eonta,in olivine showing a wide rauge of compositioll, from Fa, (pure ~lg~~iO*) to Fa,,_,,. These include the Type III carbol~aceous ~hondrites~ Table 1. Olivine cor~~~osition in the olivinepigeonite chondrites (an asterisk indicates a carbonaceous chondrito) *Bali Felix *Qrosnaja *Kaba Karoonda Lance *Xokoia Xgawi Ornans Tieschitz *Vigarano ~~arrento~
O-60 20-60 O-65 O-65 33 10-50 O-65 30 25-60 104% O-60 25-55
which however do not differ essentially in chemical and mineralogical oomposition from the non-carbonaceous olivine-pigeonite chondrites. In those meteorites with variable olivine composition, the mean composition of the olivine is near FaQB, the same as in the other chondrites of this group. The data are given in Table 1. THE OLIVI~E-BR~~ZITE AND O~~V~~E-~YP~~~~H~~E
~H~~~R~T~s
These two groups comprise over 90 percent of all chandrites, and are approximately equal in abundance. The olivine compositions of individual meteorites of these two groups are given in Table 2. 3
BRIAN MASON
1014 Table
composition in olivine-bronzite and olivine-hypersthene chondrites, in mole chondrites, olivine~bro~ite chondrites, Fe~,,_~r, olivine-hypersthene FezSiOo (Fa); (Those meteorites not recorded in the PRIOR-HEY catalog (1953) or by KEIL (1960) Fass-s,. are printed in italics and are briefly described in the Appendix. An asterisk indicates an observed fall). per
2. Olivine
cent
*Aarhus, 18; Abernathy, 23; Abe, 19; Adams County, 19; Adelie Land, 19; Akron, *Akaba, 24; *Akbarpur, 27; Albin, Alamosa, 25; *Albareto, *Alexandrovsky, 18; *Alfianello, 24; herst, 25, *Andover, 25; *Angers, 25; 23; Arcadia, 29; *Archie, 20; Arriba, *Ashdon, 25; Assam, 24; *Ass&, 19; *Aumale, 25; *Aumieres, 24; Aurora,
19; Accdana, 24; Achilles, 20; *Achiras, 25; Acme, 24; Adrian, 19; *Agen, 20; *Aguada, 25; *Air, 23; 19; Akron No. 2, 16; *Akwanga., 19; Alamogordo, 19; 22; *Aldsworth, 28; *Aleppo, 24; *Alessandria, 18; Nagla, 19; Amber, 24; Am*Allegan, 19; *Ambapur Anthony, 19; *Appley Bridge, 29; *Apt, 24; Arapahoe, 25; Artracoona, 24; *Asco, 26; Ashburton Downs, 24; *Atarra, 23; *Atemajac, 23; *Athens, 31; *Atoka, 24; 19; *Ausson, 25; *Avilez, 19; *Aztec, 24.
25; *Bandong, 28; *Banswwl, 24; *Bar*Bachmut, 24; *Bald Mountain, 24; *Baldwyn, botan, 24; *Baroti, 25; Barratta, 25; *Bath, 19, *Bath Furnace, 24; *Baxter, 24; *Beardsley, 19; Beenham, 23; BeZZe Plaine, 24; Belly River, 20; 20; *Beaver Creek, 19; *Beddgelert, *Benares, 28; *Benld, 20; *Benton, 31; Berdyansk, 25; *Berlanguillas, 25; *Bethlehem, 19; 26; *Bhagur, 25; *Bherai, 24; *Bhola, 27; *Bielokrynitschie, 20; *Beuste, 25; *Beyrout, *Birni N’konni, 18; *Bishunpur, 18; *Bjelaja Zerkov, 20; *Bjurbole, 26; *Black Moshannan Park, 24; *Blanket, 24, *Blansko, 19; Bluff, 25; *Boeas, 26; Boelus. 30; Boerne, 20; Bogoslovka, 19; Bolshaya Korta, 19; Bonita Springs, 20; *Borgo San Donino, 29; *Bori, 25; *Borkut, 26; *Borodino, 20; *Botschetschki, 26; Bowden, 18; Brady, 25, *Breitscheid, 19: *Bremervorde, 24; Brewster, 24; Briscoe, 26; Broken Bow, 20; Brownfield, 19; *13rutierheim., 24;
*Bur-Gheluai,
19; *Buschhof,
24; Bushnell,
19; *Butsura,
19.
*Cabezo de Mayo, 24; &dell, 24; ~~~l~~rn, 23; *Canellas, 17; *Cangas de Onis, 18; *Cape Girardcau , 19 ; *Caratash, 29, Carcote, 20; Caroline, 19; Carraweena, 24; C’art,oonkana., 24; Cashion, 18, *Castalia, 19; *Castine, 25; Cavour, 19; Cedar (Kansas), 18; Cedar (Texas), 18; *Coreseto, 19; *Chail, 18; Chamberlin, 18; *Chandakapur, 24; *Chandpur, 23; Channing, 19; *Chantonnay, 23; *Charsonville, 18; *Charwallas, 19; *Chateau-Renard, 25; *Cherokee 26; Chico, 27; *Chicora, 29; Clareton, 25; *Clohars, 25; Clovis, Springs, 28; *Chervettaz, 19; Cobija, 19; Cocunda, 24; Colby (Kansas), 18; *Colby (Wisconsin), 25; Coldwater, 17; *~ollesc~poli, 19; Concho, 23; Coolidge, 14; ~oomandook, 19; Coon Bmte, 24; Cope, 18; &&&a, 19; Cortcz, 19; *Cosina, 19; Cotesfield, 23; Cott~~~oo~, 18; Covert, 18; Y’ranganore, 24; *Cronstad, 18; Crosbyton, 17; *Cross Roads, 18; *Crumlin, 24; Cuero, 19; Culbert’son, 18; Cullison, 18; Cushing, 19; *Cynthiana, 25. DaEe Dry Lake, 24; ‘Dandapur, 25; *Danvillo, 23; Daoura, 23; *Darmstadt,, 19; Davy, 23; *Deal, 25; Death liulley, 20; *De Cewsville, 18; *Demina, 23; De Nova, 23; Densmore, 23; *Dhurmsala, 26; *Diep River, 25; ~~~.boola, 19; Dimmitt, 20; ~~~~~~c~, 18; Dix, 23; *DjatiPengilon, 20; *l&rmaia, 19; *Dokachi, 19; *Dolgovoli, 25; “Romanitch, 24; *Donga Kohrod 19; *Doroninsk, 19; *Dowo, 25; *Douar Mghila, 30; Doyleville, 20; *Drake Creek, 25; *Dresden, 20; DuncanviZZe, 19; *Dundrum, 19; *Durala, 25; *Duruma, 25; Dwight, 25. *Ehole, 19; *Eichstadt, 20; *Ekeby, 19; *Elenovka, 25; Eli Elwah, 23; Elkhart, 18; Ellerslie, 25; Elm Creek, 18; El Perdido, 19; Elsinora, 17; *Ensisheim, 28, *Epinal, 19; *Ergheo, 25; Erofeevka, 17; *Erxleben, 19; *Esnandes, 18; Estaeado, 19; *Eszc, 19; Eustis, 18. 18 ; *Farmington, 24; *Farmville, 18; Farnum, 25; *Favars, 18; *Payetteville, Chair, 17; *FBnghsien-ku, 18; Ferguson Switch, 1’7; *Fisher, 23; Fleming, 18; *Florence, 17; Forestburg, 24; *Forest City, 19; *Forest Vale, 17; *Forksville, 26; *Forsbach, 19; *Forsyth, 23; Franklin, 19; *Fukutomi, 24; *Futtehpur, 24. 19;
Farley, *Feid
Olivine Gail, 18; *Galapian, 19; Gerona, 19; *Gifu,
composition
1015
in chondrites
20; *Galim, 29; *Gambat, 23; Garnet& 20; Garraf, 24; *G&darn, 25; Gilgoin, 17; *Girgenti, 25; *Git-Git, 24; Gladstone, 17; *Glas-
atovo, 18; *Gnadenfrei, 18, Gnubara, 19; Goodland, 25; *Gopalpur, 20, Grady (1933), 25; Grady (1937), 15; Grant County, 26; *Great Bear Lake, 19; Gretna, 25; *Gross-Divina, 19; *Grossliebenthal, 25; *Grimeberg, 17; Gruver, 19; Gualeguaychu, 19; *Guarena, 19; *Guidder, 29; *Gumoschnik, 19; *Gurram Konda, 24; *Giitersloh, 20. *Hainaut, 19; Hale Center (No. l), 25; Hale Center (No. 2), 17; *Hallingeberg, 25; *HamI&, 27; Harding County, 26; Hardwick, 24; *HurZeton, 26; *Harrison County, 26; Harrisonville, 24; Haskell, 23; ~~~~ayu~~~, 18; Hat Creek, 18; Haven, 20; Haviland, 19; Hawk 24; Hendersonville, 24; *Heredia, Springs, 19; Hayes Center, 23; *Hedeskoga, 19; *Hedjaz, 18; Hermitage Plains, 24; *He&e, 19; Hesston, 24; *Higashi-koen, 19; *High Possil, 25; Hildreth, 25; Hinojo, 20; Hobbs, 19; *Hokmark, 24; *Holbrook, 25; Holly, 18, *Holman Island, 29; Holyoke, 19; *Homestead, 24; *Honolulu, 24; Horace (No. I), 19; Horace (No. 2), 25; Howe, 19; Hugo, 17; Hugoton, 16; *Hungen, 19. 19; Imperial, *Iehkala, 18; *Idutywa, Ioka, 23; *1&ingu, 18; Isoulane-n-Amahar,
18; Indianola, 25; *Isthilart,
24; Indio Rico, 18; 18; *Itapicuru-Mirim,
Ingalls, 18.
*Jackalsfontein, 24; *Jamkheir, 19; *Jelica, 31; *Jemlapur, 25; Jerome (Idaho), Jerome (Kansas), 19; *Jhung, 25; Johnson City, 25; Juarez, 24; *Judesegeri, 18; Junction,
20;
24; 24.
*Kadonah, 17; *Kaee, 19; QKagarlyk, 23; *Kakowa, 23; Ka~d~oner~ Hill, 19; *Kalumbi, 24; *Kamsagar, 24; *Kcmdczhur (Afghanistan), 24; *Kangra Valley, 19; Kansas City, 19; Kappakoola, 17; *Kaptal-Aryk, 23; Karagai, 23; *Karakol, 28; *Karewar, 24; *KcrZuwaZa, 23, *Karkh, 25; Karval, 19; Kaufman, 23; Kearney, 20; Kelly, 29; *Kendleton, 25; *Kerilis, 19; Kermichel, 24; *Kernouve, 18; *Kesen, 17; Keyes, 23; *Khanpur, 29; *Kharkov, 24; *Kheragur, 24, *Khetri, 18; *Khmelevka, 23; *Khohar, 23; *Kikino, 19; *Kilbourn, 19; *Killeter, 20; Kimble County, 19; Kingfisher ,23; Kingoonya, 24; Kissij, 17; *Klein-Wenden, 19; *Knyahinya, 25; Koraleigh, 24; Wrahenberg, 27; *Krasnoi.Ugol, 24; *Krymka, 18; *Kukschin, 24; *Kuleschovka, 25; K&nine, 24; *Kunashak, 24, *Kusiali, 24; *Kuttippuram, 25; *Kuznetzovo, 23; *Kyushu, 26. *La Becasse, 23; *Laborel, 19; *La Colina, 17; Ladder Creek, 25; *L’Aigle, 23; Lake Brown, 25; Lake Labyrinth, 28, Lake Moore, 25; Laketon, 25; La Lande, 24; *Lalitpur, 24; *Lancon, 19; *LZmghalsen, 26; *Launton, 23; La Villa, 19; *Lavrentievka, 24; Lawrence, 23; *Leedey, 24; *Leeuwfontein, 24; *Leighton, 20; *Leonovka, 24; *Le Pressoir, 24; *Les Ormes, 24; *Leaves, 25; *LilIaverke, 18; *Limerick, 19; Lincoln County, 24; *Linum, 23; *Lissa, 23; *Little Piney, 23; *Lixna, 20; Lockney, 23; Logan, 19; Long Island, 25; Loomis, 23; Lost Lake, 25; Loyola, 23; (the Loyola meteorite appears to be a stone from the Homestead fall). *Lua, 24; Lubbock, 24; *Lute, 24; *Lumpkin, 19; Lundsgbrd, 24; *Luponnas, 19; Lutschaunig’s St,one, 24. *Macau, 19; *Madrid, 24; Maim, 25; Makmewa, 24; *Malampaka, 19; *MaIotas, 19; *Mamra Springs, 24; ‘Manbhoom, 30; *Mangwendi, 29; *I%~ardn.~, 19; *Marion (Iowa), 24; _!arion (Kansas), 24; Marlow, 24; *Marmande, 24; Marsland, 16; *Mascombes, 24; *Mauerkirchen, 24; *Mauritius, 26; Mayday, 19; *Maziba, 25; McAdoo, 25; McKinney, 24; McLean, 19; Mellenbye, 27; Melrose, 23; *Menow, 18; *Meridi, 19; *Mern, 24; *Meru, 28; *Merua; 18; Mets@&, 18, *Meuselbach, 24; *Mezel, 24; *Mezo-Madaras, 26; *Mhow, 24; Miami, 17, *Middlesbrough, 23; *Mike, 24; *Milena, 24; *Miller (Arkansas), 19; Miller (Kansas), 19; kfinas Gerais, 25; *kfirzapur, 24; *Misshof, 19; Mission, 23: *Mjelleim, 19; *Moos, 24; *Modoc (lBO5), 23; Modoc (1948),22; *Molina, 24; *Monroe, 19; *Monte das Fortes, 24; *Monte Milone, 25; *Montlivault, 24; *Monze, 25; *Mooresfort, 19; *Moorleah, 23; *Moradabad, 24; Morland, 19; *Mornans, 19; Morven, 18; *Moti-ka-nagla, 19; *Motta di Conti, 17; Mount Morris (New York), 17; *Muddoor, 19; Muizenberg, 24; *Mullctiwu, 25; Muroc, 25; Muroc Dry Lake, 25.
BRIAN MASOJS
1016
24; *~ammiant.hal, 19; Wanjemoy, 18; *Kan Yang *~adiabondi, 18; Wagy-Borove, P&O, 24; *il’aoki, 20; Nardoo, 25 (one of the two st,ones, the other being identical with Elsinora): 19; Nazareth, 19; Neenach, 24; *Narellan 28; Naruna, 19; il’iis, 30; Nashville, 22; Wassirah, *Nerft, 23; Xess County (1894), 25; Ness County (1938), 20; New Almelo, 24; *Kew Concord, 24; Sowsom, 24; *Xkolaevkx, 19; *Nikolskoje, 24; Xorcateur, 25; *R’opan-Bogdo, 24; *Sulles, 19.
19: 30; 14;
Oakley, 21; Oberlin, 27; *Ochansk, 20; Oezeretna., 19; *&set, 25; *O-Fehert,o, 23; *Ogi, 24; Okirai, 19; *Okniny, 27; *Olivenza, *Ohaba, 20; *Ojuelos Altos, 25; Okechobee, *Olmedilla de Alarcon, 18; Orlovka, 19; *Orvinio, 23; Oshkosh, 18; *Oterwy, 25; Otis, *Ot,tawa, 29; *Oua,llen, 20; Oobari, 26; Ovid, 20; *Oviedo, 25; Ozona , 19 .
*P&c&,, 24; Pampa de Agua Blanca, 24; Pampa de1 Infierno, 24; *Pampanga, 24; *Pantar, 26; *Patrimo&o, 25; *Pavlograd, 25; Peck’s Spring, 25; 25; *Par&lee, 18; *Paragoultl, P&z, 26; Penokee, 19; *Perpeti, 25; *Perth, 28; *Per~o~na~sky, 24; Petropavlovka, 16; 24; Pinto Pevensry, 28; *Phu-Hong, 18; *Phum Sambo, 19; Pickens County, 20; Piercevillc, 18; Plainview (1917), 19; Pfainview Xountains, 24; Pipe Creek, 19; *Pirgunje, 28; *Pirthalla, (1950), %O; *Plant,ers~~ille, 20; Pleasanton, 18; *Ploschkovitz, 24; *~nompehll, 24; *Pohlitz, ‘t 5; *Pokhra., 18; Potter, 23; Prairie Dog Creek. 19; *Pribram, 20; *Pricetown, 24; Pllente18. Ladron, 24; *l?ulsora, 19; *Pultusk, *Queens
Ncrcy,
18;
‘Qrtenggouk,
19;
*&uincay,
24;
*R&co, 18; *R.akovka; 24; *Ramsdorf, 25; *Ranchapur, 19; *Ranch0 de la Press, 19; *Rangala, 25; .Ransom, 19; ~~~~~~~~,a, 20; Reager, 25; ‘Reliegos, 23; *Renca, 24; *Richardt,on, 19; *Richmond, 26; *Rich Mountain, 24; *Rio Negro, 25; *Rochester, 20; Rolla, IQ; ( W. H. Nininger has recognized five different; Rolla meteorites, but t)hey are all olivine-bronzite chondrites of similar composition, and are here treat,ed as a singlo find). Romero, 19; Rosamond Dry Lake, 24; Rosebud. 19; *Rose City, 19; Roy (1933), 25; Roy (1934), 24; Rush County, 17; Rush Creek, 26; Rushville, 24; *Ryochki, 23. St. Ann, 18; *St. Caprais-~le.~uinsac, 25; *St. Christ,oph~-la-Cha~,r~?use, 25; *St. DenisWestrom, 25; *St. Germ&in-du-Pin& 18; *hk Louis, 19; *c%. Marguerite, 20; *St. Mesmin, 29; *St. Michel, 24; St. Peter, 25; Salino, 18; *Salles, 18; Salt Lake City, 19; San Carlos, 18; San Emigdio, 20; San Joso, 18; San Pedro Springs, 23; *Santa Barbara, 25; *Santa Isabel, 24; *Saratoy, 24; *Sauguis, 25; *Savtschenskoje, 28; Schaap-Kooi, 19; *Schollin, 26; *Schonenberg, 25; Scott City, 20; J’cww~, 19; *Searsmont, 19; *Segowlie, 25; Seg&n, 20; Heibert, 18; *Scldebonrak, 19; Selma, 20; *Semarkona, 20; *Sena, 17; Seneca, 19; *Seres, 17; *S&e Lagoas, 19; *Xevilla, 28; *Sevrukovo, 25; Shafter Lake, 19; *Sharps, 28; Shaw 23, *Shelburne, 24; *Shupiyan, 19; *Shytal, 25; ,SWney, 24; *Siena, 28; Silverton (Now Sduth Wales), 25; Silverton, (Texas), 17; *Simmcrn, 19; *Sinai, 23; *Sindhri, 19; *Sitathali, 19; *Ski, 24; *Slavetic, IT; *Slobodka, 23; Smith Center, 24; *Soko-Banja, 27; Springfield, 23; *Stalldalen , 19 ; “Stavropol, 24, Sto~ington, 19; *Strathmore, 25; ~~.~~~e~te,24, *Success, 24; *Sultanpur, 26; *Supuhee, 19; Suwahib-Adraj, 23; Suwa,hib-Ain Rala, 18; Suwahib-Buwah, 14; *Sylaeauga, 20. *Tabor, 18; *Tadjera, 25; Taiban, 25; Taiga, 19, “Takenouchi, 19; *Tan&, 25; Tarbagatai, 23; Tqfa, 25; Tatum, 18; *Tauq, 25; Tern&, 25; *Tenham, 24; *Tennasilm, 23; Texline, 19; *ThaZ, 19; Thomson, 24; *Tildon, 26; *Timochin, 20; *Tirupati, 18; *Tjabe, 19; *Tjerebon, 24; *Tomakovka, 30; *Tomattan, 18; Tomhannock Creek, 18; *Torrington, 18; Tostado, 19; *Toulouse, 19; *Tourinnes-la-Grosse, 25; Travis County, 18; *Trenzano, 19; *Tromq, 18; *Troup, 28; Tryon, 24; *Trysil, 25; *Tuan Tut, 24; Tuba, 20; Tuzla, 25; T~e~~~~~n~ Patnzs, 26; *Tysnes Island, 20. *Uberaba, 19; *Uden, 30; *Udipi, 18; Ultuna, 18; Ulysses, 17; *Umbala, 23; Ute Creek, 19; *Utrecht, 24; *Utzenstorf, 18; Uvalde, 19.
28; UmmTina,
Olivine composition in chondrites
1017
*Vago, 19; *\‘aldavur, 20; *\Ta~ldinizza,24; Valkeala, 24; Valley IVells, 24; \?arpaisjarvi, 25; *Vax*ilovka 7 30.f *\Tengerovo, 19; Vera, 24; *Verkhne Tschirskaia, 18; *\‘ernon County, 19; Villedieu, 19; l’incent, 24; *Virba, 25; *Vishnupur, 30; *Vouihe, 24. Kaconda, 25; Wairarapa TTalby, 18; Waldo, 25; *Walters, 25; JVeldona, 19; Wellman, 18; *wesso1y, 18; *Weston, 19; Whitman, 19; Wickenburg, 23; IVilburton, 25; W~illowdale, 20; lV:ilmot, 18; 1Pi~ngelZilza,19; *Wit,klip Farm, 18; *Wit,sand Farm, 27; *\f%t,ckrantz, 23; *IVotd Cott,agc, 24; Woodward Coumy, 19; Wray, 15. Yandama, 25; *Vatoor, 19; *Yonoeu, 18; York, 24; ~Y~r~tou~~~,24; (A.M.K.H. specimen; specimens from the British &Iuaeum and the Chicago Nat~wai History ?;LUS
The data are most readily comprehended in the form of diagra,nls (Fig. 1). ‘I’hese show a remarkable qua,nt,ization in the olivine composition; most of the olivinebronzitJe chondrites have olivine with composition Far,_,,, most of the olivinehypersthene chondrites have olivine with composition Fa,,_,5. It is immediately apparent that, these two groups, instead of forming a co~~til~uous series as envisaged by PRIOR, are separated by a marked hiatus. This also corresponds to a significant difference in bulk composition; the olivine-hypersthene chondrites are uniformly lower in total iron (average about 21 percent)-the low-iron (L) group of UREV and CRAIG (1~~3)-thar~ are the oli~ine-bro~lzite cho~~drites (t,ttta,l Fe averages about 27 percent)---the high-iron (H) group of UREY and CRA’EG. The limits of olivine composition for the two groups are I%,,_.,, for the olivinebronzite chondrites and Pa,,_,, for the olivi~le-hypersth~~n~ chondrites. Actually, in view of the limits of precision of the ~neasurements, it is quite possible t,hat chondrites wit,h olivine of mean composition Fa,, and Fa,, are completely lacking. The boundary between the olivine-bronzite and the olivine-hypersthene chondrites is drawn between Fa,, and Fe,,. I propose that this definition replace the original de~llit,ion of Prior based on chemical analysis, since the olivine com~~osition is more readily and possibly more accurately determinable than the FeO/MgO ratio in the bulk composition of the meteorite. With this definition the composition of the orthopyro~elle in the olivine-bronzite chondrites will always correspond to the definit,io~ of bronzite used by PRIOR---an orthopyroxene containing 10 to 20 mole percent FeSiO,-since the FeO/iMgO ratio in the orthopyroxene of chondrites is uniformly lower than this ratio in the olivine. It is possible that the orthopyroxcne in some of the olivine-hypersthene chondrites may contain sightly less than 20 mole percent FeSiO,, but this should cause no confusion in classification if olivine composition is used as the criterion. The total range of olivine composition in these meteorites is Fa,,_,,. The upper limit (%‘a,,) is readiIy explicable, since in meteorites with olivine of this composition virtually all the available iron is combined in the ferromagnesian silicates, there being essentially no metallio iron present. The lower limit (Fa,,) presents a problem for which there is no ready explanation. There is no obvious reason why more highly reduced olivine-bronzite chondrites (i.e. those with more free iron and less iron combined in the silicates) should not exist. Nevertheless, there is a complete
BRIANMASON
1018
80 OIlvine-bronzlte 70
60 g E
-
50
-
40 30 20
E B u
_~
10
E” ‘0 II
100
E z”
90
__
80
-
70
-
60
-
50
_
40
_
30
-
kz d
20
-
_..
10 -
10
15
20
25
30
35
Fig. 1. Distribution of olivine composition in olivine-bronzite olivine-hypersthene chondrites.
and
hiatus between the olivine-bronzite chondrites and the enstatite chondrites (in which all or practically a,11the iron is in the reduced state, and none or very little is present in the silicates). The numbers of meteorites in each of the two groups is given in Table 3. Considering the data for observed falls, of the 466 total, 196, or 42%, are olivinebronzite chondrites, 270, or 58’$&, are olivil~e-hypersthene chondrites. The numbers of each group are probably sufficiently large to justify the conclusion that olivinehypersthene chondrites have a somewhat greater absolute abundance than the olivine-bronzite chondrites. When we compare the relative numbers of finds versus observed falls in the two groups, we see that 53% of the olivine-bronzite chondrites are observed falls, compared to 64% of the olivine-hypersthene chondrites. In other words, oli~ine-bronzite chondrites occur more abundal~tly as finds than do the olivine-hypersthene chondrites. This is readily understandable in view of the general physical properties of the two groups; the olivine-bronzite chondrites contain much more nickel-iron (about 20%) than do the olivinehypersthene chondrites (about 8%). The nickel-iron tends to cement the silicate
Olivine composition in chondrites
1019
phases and give the meteorite a greater mechanical strength. In addition, the weathering of the nickel-iron causes an additional cementation through the chondrites are deposition of secondary iron oxides. Thus the o~vine-hypersthene probably much more rapidly broken down by weathering than are the olivinebronzite chondrites, and hence do not survive for so long periods on the Earth’s surface. It is no chance event that the majority of the finds of stony meteorites in the United StatSes have been tough limonitized olivine-bronzite chondrites. In view of the comparative large numbers of meteorites in each of these two groups, a study was made of dates and times of fall to see whether any statistically valid differences could be observed, either for hour of fall, day of fall, or month of fall. No marked differences were observed between the two groups. For each group the plot of hour of fall gave comparable curves, rising from a minimum in the early morning hours to a maximum between 3 p.m. and 5 p.m. and then falling Table
3. Numbers of olivine-bronzite and olivine-hypersthene chondrites enumerated in Table 2
Olivine-bronzite Olivine~hypersthene Totals
Falls 196 270
Finds 168 157
All 364 427
466
325
791
again. Analysis of the information for date of fall also shows a fairly regular distribution throughout the year, without any significant concentration of falls on specific dates; more have been observed to fall in the summer months than in the winter, but this is presumably a natural consequence of more favorable weather for observation and collection during the summer. Possibly a more searching analysis of the data, by narrowing the composition ranges and also taking into account the internal structure (degree of chondricity, etc.), might reveal some regularities of fall indicating a recurrence of specific meteorite types at regular inte~als. In view, however, of the extremely low percentage recovery (of the 500 meteorites estimated by Brtow~ (1961) to fall on the Earth each year the average recovery is between 4 and 8), the chance of discovering significant statistical informatiou from the analysis of data on observed falls cannot be great. DISCUSSION The data presented here clearly call for an explanation in any theory of the origin of the chondrites. PRIOR (1920) appreciated the marked overall chemical and mineralogical uniformity of the chondrites, and proposed that the different groups had been formed by the progressive oxidation of a highly reduced magma, t,he earliest stage being represented by the enstatite chondrites. Conversely, NASOH (1960) and RIMSWOOD (1961) have theorized that the parent material was highly oxidized, its original state being similar to that of the carbonaceous chondrites, the other groups of chondrites having been produced from this material by dehydration and progressive reduction. URSY and CRAIG (1953), from the occurrence of high-iron and low-iron chondrites, have argued that these types must have been
1020
BRIANMASON
derived from at least two asteroids of different composition. FISH, GOLES, and ANDERS (1960) have developed the theory that the different groups of chondrites (and the other meteorite types) were developed in bodies of asteroidal dimensions. RINGWOOD (1961) has presented a comprehensive theory for the origin of all meteorites within a single body of lunar or planetary dimensions. WOOD (1962) favors an origin of the different types of chondrites from different depths within a planetary body, the chondrules themselves having condensed as liquid droplets from cooling solar gases during the formation of the sun, and later aggregating into planets and asteroids. In my 1960 paper I wrote “Some of the facts regarding the chondrites are inconsistent with their origin either as massive fragments of a disrupted planet or The mineralogy of the typical caras aggregated dust from such a disruption. bonaceous chondrites.....shows that they have never been above 600” C and probably have always been at much lower temperatures. The texture and structure of the non-carbonaceous chondrites show that they are not fragments of a disrupted planet, for then gravitational segregation of silicate and metal should have taken place. Their mineralogy, especially the uniformity of composition of olivine and pyroxene in each individual meteorite, shows that they are not chance aggregates of dust but individual chemical systems in phase equilibrium. Their compositions are consistent with an origin by recrystallization of the material of carbonaceous chondrites. Such an origin does not require that they were ever part of a body or bodies of planetary or lunar dimensions, and their texture, their structure, and their mineralogy speak directly against such an origin”. It appears to me that the much more extensive data given in the present paper With some trepidation I venture in no way contradicts this earlier summation. to propose a theory for the origin of chondrites alternative to those outlined previously. Is it possible that the chondrites predate the formation of the larger bodies in the solar system! Are the different types of chondrites samples from different regions within a primordial dust cloud from which the planets aggregated! One can imagine this primordial dust cloud as a rotating lensoid body of gas and solid particles, varying in temperature, pressure, and composition from the center to the outer margin. The solid particles would tend to accumulate in an equat’orial zone. The temperature at the outer margin would be near absolute zero and would presumably increase towards the center, and the composition of the solid matter would change correspondingly, from frozen volatiles with little nonvolatile material near the margin to more refractory material towards the center. The discontinuities and hiatuses between the different chondrite groups may perhaps reflect incipient segregation and zonal aggregation within this equatorial band of solid particles. If we accept the logical succession from cold oxidized material at the outer margin to hotter and more reduced material towards the center, then this succession is represented among the chondrites by the sequence: carbonaceous chondrites (Type I)-carbonaceous chondrites (Type II)-olivinepigeonite chondrites-olivine-hypersthene chondrites-olivine-bronzite chondrites -enstatite chondrites. While this presents a broadly consistent picture, it is not obvious why the olivine-hypersthene chondrites contain 5 percent less total iron than chondrites in the other groups, nor why there should be a hiatus in the reduction
Olivine composition in chondrites
1021
sequence between the olivine-bro~zite chondrites and the enstatite chondrites. Perhaps the loss of iron from the material which formed the olivine-hypersthene chondrites was the result of its removal by a reaction which took place under rather specific conditions of temperature, pressure, and chemical environment (possibly The hiatus between the formation of a volatile iron compound such as a carbonyl). the olivine-bronzite chondrites and the enstatite chondrites may reflect an early segregation of the primordial dust cloud into different zones. In essence, therefore, I would suggest the possibility t,hat the chondrites represent sintered masses of pre-planetary material which in most insta,nces represent rlear-equilibrium for the temperature, pressure, and chemical environment The great preponderance of olivine-br0r~zit.e and olivinein which they formed. hypersthene chondrites can perhaps be ascribed to their representing the equilibrium conditions within large regions of the ancestral dust cloud and/or to their having originated within the general region of the terrestrial planets and the asteroidal belt. This concept that the chondrites have a pre-planetary origin is supported by recent work on their dating by the xenon method. BUTLER, JEFFEI~Y, REYNOLDS, and WASSERBCRG (1963) interpret the results of this work to indicate that the Earth post-dates the meteorites by about 200 million years. A~kno~~e(~gme~ts-The work reported in this paper has been supported (~~F~Gl4~47) from the Xational Science Foundation.
by a. research
grant
REFERENCES (1961) The density and mass distribution of meteorite bodies in t,hr neighbourhood of the Earth’s orbit. J. Geophys. Res. 68, 1316-1317. BUTLER IV. A., *JEFFREY P. M., REYNOLDS J. II. and WASSERBDR~ G. J. (1963) Isotopic variations in terrestrial xenon. J. Geophya‘. 12~. 68 (in press.) Frsa 12. A., GOLES G. G. and ANDERS E. (1960) The record in the meteorites. III. On the development of meteorites in asteroidal bodies. J. Astrophy. 132, 243-258. KEIL K. (1960) Fortschritte in der Meteoritcnkunde. Fortschr. Mineral. 38, 202-283. MASON B. (1960) The origin of meteorit,es. J. Ceophys. l&s. 65, 2965-2970. MASON B. (1962) The classification of the chondritic meteorites. A,mer. *~~~~~e~~rn _~~)~,~t~es 2085,20 pp. XARON R. and Wrrx H. 3. (1962) The Renazeo meteorite. Amer. ~~~z~se~~?n _~~~~~it~tes2106. I1 BROWN
R.
PP. PRIOR G, T. (1920) The classification of meteorites. Nin. Mug. 19, 51-63. PRIOR G. T. (1953) Catalogue cfl ~Weteorites. Second edition, revised by M. H. Hey, British Museum, London, 43.2 pp. RINGWOOD A. E. (1961) Chemical and genetic relationships among meteorites. G’eochim. et Cosmochim. Acta 24, 159-197. UREY H. C. and CRAIG H. (1953) The composition of the stone meteorites and the origin of the meteorites. Geochim. et Cosmochim. Actu 4, 36-82. WIIK H. B. (1956) The chemical aomposition of some stony meteorites. Geochim. et Cosmonhim. Acta 9, 279-289. WOOD J. A. (1962) Metanlorphis~~ in ohondrites. Ceochim. et Cosmochim. Acta 26, 739-750. YODF,R H. S. and SAHAMA T. C. (1957) Olivine X-ray determinat,ive curve. Amer. Mi?z. 42, 475-.491.
1022
Bmasr MASON APPENDIX
Meteorites mentioned in this paper which sre not recorded in the PRIOR-HEI’ catalog (1953) or by KEIL (1960).
Akron No. 2, Washington Caunty, Colorado; 40” 09’N, 103” 1O’W; found 1954; 0.64 kg. Akwanga, Nigeria; 8” 55’ N, 8” 26’ E; fell July 2, 1959; 3 kg. Ashburton Downs, Tniestern Australia; 23” 20’ S, 117” 06’ E; 1.8 kg. Belle Plaine, Sumner County, Kansas; 37” 19’ N, 97” 15’ W; found 1955; 24 kg. Bruderheim, Alberta, Canada; 53” 54’ N, 112” 53’ W; fell March 4, 1960; 300 kg. Calliham, McMullen County, Texas; 28” 25’ N, 98” 15’ W; found 1968; 40 kg. Clovis, Curry County New Mexico; 34” 18’ N. 103 08’ W; found 1961; 283 kg. Cocunda, Soubh Australia; 32” 49’ S, 134” 49’ E; found 1945-46; 0.5 kg. Coomandook, South Australia; 35” 25’ S, 139” 45’ E; found 1939; l*l kg. Cordoba,, Rio Negro, Argentina; 40” 09’ S, 68” 30’ W; fall? Cot*tonwood, Yavapai County, Arizona; 34” 50’ N, 112” 01’ W; found 1955; 0.8 kg. C’rosbyt,on, Crosby County, Texas; 33” 40’ N, 10X” 16’ W; find. Dale Dry Lake, San Bernardino County, California; 34” 02’ N, 115” 54’ W; found 1957; O-3 kg. Death Valley, Inyo County, California; 36” 21’ N, 116” 49’ W; found 1956. Dimboola, Victoria, Australia; 36” 30’ S, 142” 02’ E; found 1944; 16 kg. Dispatch, Smith County, Kansas; 39” 30’ N, 98” 32’ W; found 1956; O-22 kg. Djermaia, Chad, Africa; fell February 25, 1961; Dosso, Niger, Africa; 13” 03’ xi, 3” 10’ E; fell February 19, 1962; I.25 kg. Duncanvillc, Dallas County, Texas; 32” 38’ N, 96” 52’ W; found 1961; 17.8 kg, Whole, Angola, Africa; 17” 18’S, 15” 50’ E; fell Augusts 31, 1961; 2.4 kg. Esu, Sudan, Africa; fell March, 1941; 3.2 kg. Forestburg, Montague County, Texas; 33” 30’ N, 97” 39’W; found 1957; 26.6 kg. C+eidam, Nigeria; 13” N, 11” 52’ E; fell July 6, 1950; 0.72 kg. Namlett Starke County, Indiana; 41” 20’ N, 86” 35’ W; fell October 13, 1959; 2.95 kg. Hark&on, Harrison County, Texas; 32” 41’ N, 94” 31’ W; fell May 30,1961; 8.3 kg. IIassayampa, Maricopa County, Arizona; about 33” 45’ N, 112“ 40’ W; find; Hokmark, ~‘~sterbotten, Sweden; 64” 26’ N, 21” 13’ E; fell June 9, 1954; 0.30 kg. Ioka, Duchesne CYount,y,Utah; 40” 15’ N, 110’ 05’ W; found 1931; 31 kg. Ishinga, Tanganyika; 8” 56’ 8, 33” 48’ E; fell October 8, 1954; 0.13 kg. Jerome, Jerome County, Idaho; 42” 38’ N, 114” 50’ W; found 1954; 6.8 kg. Juarez, Buenos Aires province, Argentina; 37” 33’ 5, 60” 09’ W; found before 1938; Maldoonera :Flill, South Australia; 32” 30’ S, 134” 57’ E; found before 1956; 7 kg.
6.1 kg.
Kandahar, Afghanistan; 31” 36’ N, 65” 47’ E; fell November, 1959. Karluwala, West Pakistan; 31” 35’ N, 71” 36’ E: fell July 21, 1955, Lake Moore, Western Australia; 29” 51’ 5, 117” 33’ E; found before 1959; 13.6 kg. La Villa, Hidalgo County, Texas; 26” 16’ N, 97” 54’ W; found 1956; 19.8 kg. Mardan, West Pakistan; 34” 14’ N, 46” 46’ E; fell May 8, 1948. Marion, Marion County, Kansas; 38” 15’ K, 97’ 10’ W; found 1955; 2.89 kg. Mayday, Riley County, Kansas; 39” 28’ N, 96” 55’ W; found 1955; 6.9 kg. Metsakylb, Finland; 60” 39’ N, 27” 04’ E; found 1938; 1 kg. Oshkosh, Winnebago County, Wisconsin; 44” 02/N, 88” 33’W; found 1961; 0-I kg. Race, Tuouman province, Argentina; 26” 40’ S, 65” 27’ W; fell November 17, 1957; 5 kg. Rawlinna, Western Australia; 30” 22’S, 125“ 21’ E; found before 1959; 0.13 kg. Reager, Norton County, Kansa.s; 39” 47’ N, 100” 00’ W; found 1948; 0.23 kg. St. Louis, St. Louis County, Missouri; 38” 42’ N, 90” 14’ W; fell December 16, 1956; I kg. Scurry, Scurry County, Texas; 326” N, 101” W; found 1937; 115 kg. Seguin, Sheridan County, Kansas; 39” 22’ N, 100” 38’ W; found 1956; 6.75 kg. Sidney, Cheyenne County, Nebraska; 41” 03’ N, 102” 54’ W; found 1941; 6 kg. Sublette, Haskell County, Kansas; 37” 30’ N, 100” 50’ W; found 1952; 1.3 kg. Taiga; no information available (received from Dr. J. ZBhringer, Heidelberg). Tarfa, Saudi Arabia; 18’ 18’ h’, 58” 18’ E; found 1954.
Olivine
composition
in chondrites
10’3
Thal, West Pakistan; 33” 24’ N, 70” 36’ E; fell June, 1950. Temple, Bell Cormtg, Texas; 31” 07’ N, 97” 18’ W; found 1959; 0.2 kg. Twentynine Palms, San Bernardino County, Califo~ia; 34” 04’ N, 115’ 57’ W, found 1955; 19.6 kg. Valkeala, Finland; 61” 03’ N, 26” 50’ E; found May 1962; 0.4 kg. Vincent, South Australia; 36” 07’ S, 139” 53’ E; found before 1930; 0.4 kg. 37” 32’ N, 98” 22’ W; found 1951; 3 kg. Willowdale, Kingman County, Kansas; Wingellina, Western Australia; 26” 03’S, 128’ 57’ E; found 1958; 0.2 kg. Yorktown, West,chester County, New York; 41” 17’ X, 73” 49’ W; fell September 1869; 0.2 kg.