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The Ras Tanura, Saudi Arabia, Chondrite ABSTRACT The Ras Tanura meteorite, which fell near Dhahran, Saudi Arabia, on 23 February 1961, is an olivine-bronzite (H6) chondrite; principal minerals are olivine and orthopyroxene, with minor amounts of plagioclase, nickel-iron, and troilite, and accessory chromite and whitlockite. The Ras Tanura meteorite was an observed fall on 23 February 1961 at approximately 1142 GCT. An eyewitness at Dhahran, about 40 km south of the point of fall (26°40'N, 50°09'E) described the event as follows: A distinct boom similar to a sonic boom was heard, followed by a rolling rumble, like thunder. In an otherwise perfectly clear sky there appeared a dense white cloud with a less dense zig-zag tail trailing away to the south. The tail indicated a track from south to north. The tail disappeared after about 10 minutes. The dense white cloud persisted for about 30 minutes. During this time it drifted slowly to the east about 15°. The cloud diameter subtended an angle of about 2°. The elevation angle was about 60°. The object was observed on an azimuth of approximately 10°. A single small crusted stone, weight approximately 6 grams, is all that was recovered. It was picked up on the South Pier of the Aramco refinery at Ras Tanura. One observer believed he saw a waterspout offshore as if caused by a falling body "shortly after the explosion." It is thus probable that the main mass of the meteorite fell in the sea. Brian Mason, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560. Brian Mason 83 The stone was turned in to Aramco officials, who forwarded it to the Air Force Intelligence Center, Wright-Patterson Air Force Base, Ohio, as an unidentified flying object. It was eventually transferred to the Smithsonian Astrophysical Observatory and thence to the National Meteorite Collection, where it is cataloged as USNM 2171. Ras Tanura is a well-recrystallized olivinebronzite chondrite, H6 in the Van Schmus-Wood classification. A cut surface shows abundant metal particles in a pale gray matrix; no chondrules are visible. A slight amount of rusting has taken place in association with the metal particles. In thin section the meteorite shows an allotriomorphicgranular texture. Average grain size is approximately 0.1 mm, but with scattered larger olivine grains, up to 0.5 mm. Sparse chondrules are recognizable by textural differences, principally a coarser grain size and interstitial fine-grained material (probably devitrified glass), and by a vaguely circular outline. The principal minerals are olivine and orthopyroxene. Microprobe analyses give a composition of Fa^.o for the olivine and Fs174 for the orthopyroxene; the orthopyroxene contains 0.75% CaO. A small amount of diopside, composition Wo44En50- Fs6, is associated with the orthopyroxene; the diopside contains 0.53% Na2O, 0.31% TiO2, and 0.73% Cr2O3, whereas the orthopyroxene contains
Geochemical Differences among Components of the Allende Meteorite ABSTRACT Four discrete groups of inclusions have been distinguished in the Allende meteorite. Group I are melilite-rich chondrules; Groups II and III are aggregates made up largely of spinel and fassaite; Group IV are olivine-rich chondrules and aggregates. Groups I, II, and III have been previously classed together as Ca/Al-rich inclusions, but each group has a distinctive trace-element pattern, most clearly shown by the lanthanide distribution. Group I has a relatively unfractionated pattern (with a small positive Eu anomaly) at about 10—15 times chondrites; Group II a highly fractionated pattern with depletion of the heavier lanthanides and negative Eu and positive Tm and Yb anomalies; Group III an unfractionated pattern at about 20 times chondrites, except for negative Eu and Yb anomalies; Group IV a relatively unfractionated pattern at 2-4 times chondrites. The Yb anomalies can be ascribed to highly reducing conditions producing Yb 2+ , or to fractional condensation in a cooling nebula; the Tm anomaly may be due to fractional condensation or some unrecognized factor. The complex pattern of trace element distribution in these Allende inclusions indicates a complex history of formation of this meteorite from the ancestral nebula. Introduction The fall of the Allende meteorite on 8 February 1969, provided a large amount of a Type III carbonaceous chondrite for research. A detailed description of the fall and recovery, and of the Brian Mason, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560. Philip M. Martin, Geology Department, University of Leicester, Leicester LEI 7RH, England. Brian Mason and Philip M. Martin 84 chemical and mineralogical composition of the meteorite has been published by Clarke, et al. (1971). The following principal components were distinguished and their volume percentages estimated by point-counting: matrix, largely of Fe-rich olivine (^60%), Mg-rich chondrules (
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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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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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