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NUMBER 19 Dodd, R. T., Jr. 1971. The Petrology of Chondrules in the Sharps Meteorite. Contributions to Mineralogy and Petrology, 31:201-227. Dodd, R. T., Jr., W. R. Van Schmus, and D. M. Koffman 1967. A Survey of the Unequilibrated Ordinary Chondrites. Geochimica et Cosmochimica Acta, 31(6):921- 951. Fredriksson, K., E. Jarosewich, and J. Nelen 1969. The Sharps Chondrite—New Evidence on the Origin of Chondrules and Chondrites. Pages 155-165 in P. Millman, Meteorite Research. Dordrecht: D. Reidel Publishing Company. 103 Jarosewich, E. 1966. Chemical Analysis of Ten Stony Meteorites. Geochimica et Cosmochimica Acta, 30:1261-1265. Mather L. Bryant, Jr. 1938. A New Meteorite from Maryland. The Natural History Society of Maryland Bulletin, 8(8)-.63-68. 1954. Maryland Meteorites. Maryland Naturalist, 24(1- 4):2-18. Van Schmus, W. R., and J. A. Wood 1967. A Chemical-petrologic Classification for the Chondritic Meteorites. Geochimica et Cosmochimica Acta, 31:747-765.
Mineralogical and Chemical Compositions of Silicate Inclusions in the El Taco, Campo del Cielo, Iron Meteorite ABSTRACT The silicate minerals in these inclusions (olivine, orthopyroxene, diopside and a sodic plagioclase) have the same composition as silicates in chondrites except for a lower FeO-content of the mafic minerals and a lower K-content of the feldspar. Small grains of K-feldspar occur with the plagioclase. Olivine contains 3.5% to 4.5% FeO, orthopyroxene 3.8% to 4.6% FeO. The range of compositions within one inclusion is smaller, however, and distinct differences in mean FeO-content occur between different inclusions; the fayalite to ferrosilite ratio varies from inclusion to inclusion. The outer zone of olivine and pyroxene grains is depleted in iron oxide compared to the central part. Thus three types of disequilibria occur: (1) disequilibrium between different inclusions, (2) disequilibrium between olivine and pyroxene in a given inclusion, and (3) disequilibrium within single olivine and pyroxene grains. Both the mineral composition and the bulk chemistry of the silicate part of the inclusions are close to normal chondrites, if compared on an iron-free basis. Variations that do not seem to be caused by nonrepresentative sampling are found between different inclusions. The variations affect mainly the elements Ca, Al, and the alkalies. They can be explained by the removal of diopside and/or feldspar from a chondritic material, perhaps through partial melting. Other features suggest that the lower iron content of the mafic minerals was produced by reduction of chondritic silicates. Frank Wlotzka, Max-Planck-Institut fur Chemie, Mainz, Germany. Eugene Jarosewich, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560. Frank Wlotzka and Eugene Jarosewich 104 Introduction The El Taco meteorite is one of the Campo del Cielo, Argentina, irons. It was recovered by an expedition described by Cassidy, et al. (1965). The El Taco specimen, which weighed 2000 kg, was cut at the Max-Planck-lnstitut fur Chemie at Mainz, Germany (Hintenberger, Schultz, and Weber, 1969). Three cuts were made parallel to the longest axis of the meteorite, so that two slices of about 2 cm thickness and two end pieces resulted. One of the slices (slice A, Figure 1) is on exhibit in the Meteorite Hall of the National Museum of Natural History, and the other (slice B) was made available for research by the Max-Planck-Institut fiir Chemie, Mainz. Slice A revealed a large number of silicate inclusions (Figure 1). One inclusion of this kind had already been found in the El Toba specimen of Campo del Cielo and described by Park, Bunch, and Massalski (1966). Silicate inclusions are known from other iron meteorites, for instance, Linwood (Henderson and Perry, 1949), Woodbine (Mason, 1967), Netschaevo (Olsen and Jarosewich, 1971), and Odessa (Marshall and Keil, 1965). A thorough description of the mineral compositions of the silicate inclusions from most of the iron meteorites known to contain them was given by Bunch, Keil, and Olsen (1970). All these iron meteorites (except Netchaevo) belong to the same chemical group IAB ofWasson(1970). In continuation of earlier work (Wlotzka and Jarosewich, 1969), this paper describes the mineralogy and the bulk chemical composition of a
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SMITHSONIAN CONTRIBUTIONS TO THE EA
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Contents MINERALOGY COMPOSITION OF
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Constituent SiO TiO Al 0 fl 2 3 Cr
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PER CENT CBLCIUM FIGURE 3.—The ca
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Constituent TiO,, 2 2 3 FeO* MnO Mg
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20 Cfl 40 .60 SMITHSONIAN CONTRIBUT
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35'50' I L 6.. 3.. 2.. r FOKT DEFIA
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12 SMITHSONIAN CONTRIBUTIONS TO THE
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14 20 SMITHSONIAN CONTRIBUTIONS TO
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16 Constituent Si0 2 TiO2 A12O3 Cr
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18 20 40 £0 SMITHSONIAN CONTRIBUTI
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20 40 20 SMITHSONIAN CONTRIBUTIONS
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Abyssal Basaltic Glasses as Indicat
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24 Electron-M icroprobe Analysis An
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30 Hill in the NE Atlantic, and fro
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32 cores the arrangement is stratig
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36 ATLANTIC OCEAN LAT. LONG. DEPTH
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