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Displaying 21 - 30 from the 33 total records
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Mineral Sciences Investigations 1974-1975
Brian Mason, editor
125 pages, 48 figures, 37 tables
1977 (Date of Issue: 9 March 1977)
Number 19, Smithsonian Contributions to the Earth Sciences
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Nine short contributions from the Smithsonian's Department of Mineral Sciences for 1974 and 1975 are gathered together in this volume. These contributions comprise an account of the composition of garnet xenocrysts from three kimberlite pipes in Arizona and New Mexico; a catalog of major element chemistry of abyssal volcanic glasses, and the application of these data to determine magma compositions; descriptions of the Harleton (Texas), St. Mary's County (Maryland), and Ras Tanura (Saudi Arabia) chondritic meteorites; a comparative study of eight chondrite meteorites from India and Pakistan; geochemical data on separated components of the Allende carbonaceous chondrite; and a mineralogical and chemical study of silicate inclusions in the El Taco mass of the Campo del Cielo iron meteorite.

Mineral Sciences Investigations 1976-1977
Robert F. Fudali, editor
73 pages, 22 figures, 20 tables
1979 (Date of Issue: 11 September 1979)
Number 22, Smithsonian Contributions to the Earth Sciences
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This volume is comprised of six short contributions reporting the results of some of the research carried out by the Department of Mineral Sciences, Smithsonian Institution, during the period 1976-1977. Included are: a comparison of impact breccias and glasses from Lonar Crater (India) with very similar specimens from the moon; petrographic descriptions and chemical analyses of virtually all the known pyroxene-plagioclase achondrite meteorites and a discussion of the relationships within this class; a comparative chemical study of sixty Australian tektites from widely separated localities; a description of a new, rapid technique of sample preparation for whole-rock analyses using the electron microprobe; an interlaboratory comparison of the precision and accuracy of electron microprobe analyses; and a tabulation of the chemical compositions of some electron microprobe reference samples.

Mineral Sciences Investigations, 1969-1971
William G. Melson, editor
94 pages, 34 figures, 34 tables
1972 (Date of Issue: 16 August 1972)
Number 9, Smithsonian Contributions to the Earth Sciences
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Seventeen short contributions from the Smithsonian's Department of Mineral Sciences from 1969 to 1971 are gathered together in this volume. The scientific and technological subjects treated in these contributions include studies of lunar samples from Apollo 12, meteorites, petrology and volcanology, and descriptive mineralogy, as well as of the history and description of one of the Smithsonian Institution's most important recent acquisitions the Carl Bosch Collection of Minerals and Meteorites.

Mineral Sciences Investigations, 1972-1973
George S. Switzer, editor
88 pages, 29 figures, 28 tables
1975 (Date of Issue: 2 July 1975)
Number 14, Smithsonian Contributions to the Earth Sciences
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Thirteen short contributions from the Smithsonian's Department of Mineral Sciences for 1972 and 1973 are gathered together in this volume. Scientific contributions include new data on some mercury minerals from Terlingua, Texas; a description of dashkesanite from St. Paul's Rocks; a note on high-alumina basalt from the Aleutian Trench; descriptions of samples from the Apollo 15 and 16 lunar missions; chondrule composition of the Allende meteorite; the Pulsora meteorite and metamorphic equilibration in chondrites; the possible survival of very large meteorites that encounter the earth's surface; data on eight observed-fall chondritic meteorites; chemical analyses of two microprobe standards; and a technological note on the preparation of multiple microprobe samples. A history of mineral sciences in the Smithsonian Institution and a list of meteorites in the Smithsonian collections complete the volume.

Mineralogy, Mineral-Chemistry, and Composition of the Murchison (C2) Meteorite
Louis H. Fuchs, Edward Olsen and Kenneth J. Jensen
39 pages, 19 figures, 9 tables
1973 (Date of Issue: 14 August 1973)
Number 10, Smithsonian Contributions to the Earth Sciences
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The Murchison meteorite shower, September 28, 1969, occurred in and around Murchison, Victoria, Australia. Chemical and mineralogical analyses established it as a type II carbonaceous chondrite (C2). Murchison consists largely of fine-grained black matrix which has been identified as primarily a mixture of two iron-rich, low-aluminum chamosite polytypes. Contained in the matrix are four main types of inclusions: (1) single crystals and crystal fragments, (2) loosely aggregated clusters of crystals ("white inclusions"), (3) discrete true chondrules, (4) xenolithic fragments of two other meteorite types (mostly a unique kind of C3 chondrite).

The first type of inclusions consists of unzoned and highly zoned olivines, unzoned (disordered and ordered) orthopyroxenes, clinoenstatite, and rare diopside. Prominent minor phases are calcite, chromite, metal (with occasional traces of schreibersite), troilite, pentlandite, and two phases that could not be fully characterized.

The second type of inclusions consists primarily of grains of olivine (Fa 0 to Fa 40), lesser low-Ca pyroxenes, and minor spinel, calcite, whewellite, hibonite, perovskite, chromite, pentlandite, and rare Ca-pyroxene.

The true chondrules consist of olivine, Ca-poor pyroxene, occasional metal, and, in rare instances, one of the poorly characterized phases. The chondrules are not texturally typical of the ordinary chondrites, but resemble more closely those chondrules seen in C3 and C4 chondrites.

The fourth type of inclusion consists mainly of distinct xenolithic fragments of a light blue-gray chondrite type that resembles certain C3 chondrites (like Vigarano), though not in all aspects. These xenolithic fragments consist of disequilbrated olivines and pyroxenes, abundant pentlandite and troilite, and virtually no metal. In addition, a single xenolithic fragment was found of an unknown meteorite type.

Ca- and Al-rich glasses (of varying compositions) are found as blebs, with or without gas bubbles, contained within olivine crystals. The average Ca/Al ratio of these glasses approximates that for all meteoritic matter. They may represent early (nonequilibrium) subcooled condensates from the solar nebula. This nonequilibrium stage was apparently followed by equilibrium condensation through intermediate to low temperatures at which the layer-lattice phases condensed in abundance and incorporated crystals and fragments of the higher temperature phases.

Minor and Trace Elements in Meteoritic Minerals
Brian Mason and A. L. Graham
17 pages, 1 figure, 17 tables
1970 (Date of Issue: 17 September 1970)
Number 3, Smithsonian Contributions to the Earth Sciences
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Nickel-iron, troilite, olivine, pyroxenes, plagioclase, chromite, and phosphate minerals (chlorapatite and/or merrillite) have been separated from a number of meteorites (Modoc, St. Severin, Winona, Haraiya, Marjalahti, Springwater, Johnstown, Mt. Egerton, Soroti) and analyzed for minor and trace elements with the spark-source mass spectrometer. The elements Ni, Co, Ge, As, Ru, Rh, Pd, Sn, Sb, W, Re, Os, Ir, Pt, and Au are concentrated in nickel-iron: Se and Ag in troilite; Th, U, and the lanthanides in the phosphate minerals and in diopside; Eu, Sr, Ba, Rb, and Cs in plagioclase. Molybdenum and tellurium are concentrated in nickel-iron and troilite. The elements Ti, Sc, V, Cu, Zn, Mn, and Ga are distributed over several coexisting minerals.

Occurrence, Distribution, and Age of Australian Tektites
R. O. Chalmers, E. P. Henderson and Brian Mason
46 pages, 17 figures, 10 tables
1976 (Date of Issue: 9 September 1976)
Number 17, Smithsonian Contributions to the Earth Sciences
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Extensive field work has shown that the Australian strewnfield is less extensive than previously thought, being essentially restricted to the region south of latitudes 24? to 25?S. The few australites found north of this region probably represent specimens transported by man. Throughout much of the desert interior australites are weathering out of a late Pleistocene or early Recent horizon in a well-consolidated calcareous red sandy aeolianite; field evidence indicates that in most places they are found essentially where they fell, or stream erosion and sheet wash has transported them short distances and concentrated them in claypans and playas. Distribution within the strewnfield is irregular and can be ascribed to: (1) original nonuniform fall; (2) burial by recent deposition; (3) removal by erosion. Australites (excluding the doubtful HNa/K type) show a continuous range of composition from 80% to 66% SiO2 with related variations in other major constituents, which is reflected in the range of specific gravities (2.36-2.52) and refractive indices (1.493-1.529). The composition range is not uniform over the strewnfield, the high-silica australites being concentrated along a northwest trending band extending from western Victoria to the Lake Eyre region. Other noteworthy features are: (1) a variation in the average size of australites from place to place, those on the Nullarbor Plain being notably smaller (average < 1 gram) than those of other regions (average 3-5 grams); (2) the occurrence of many large australites (> 100 grams) in the southwestern part of Western Australia.

Unsolved problems include: (1) the inconsistency between geological age (7000-20,000 years BP) and K-Ar and fission track ages (700,000-860,000 years); (2) the relationship, if any, between australites and the  microtektites in Indian Ocean sediments; and (3) the source region of the australite material.

Partially Melted Kyanite Eclogite from Roberts Victor Mine, South Africa
George Switzer and William G. Melson
9 pages, 5 figures, 6 tables
1969 (Date of Issue: 15 April 1969)
Number 1, Smithsonian Contributions to the Earth Sciences
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Three specimens have been studied of the rare kyanite eclogite nodules in kimberlite from the Roberts Victor mine, South Africa. All are essentially the same with the primary assemblage: kyanite, omphacite, garnet, diamond (in one sample), chrome diopside, and rutile. There is also present a fine-grained secondary assemblage that appears in two forms: (1) primary omphacite altered to a mixture of plagioclase, clinopyroxene, and possibly glass; and (2) thin layers along omphacite, kyanite, and garnet grain boundaries. These layers have a clear-cut igneous texture and consist of plagioclase microlites with glass or devitrified glass, or plagioclase microlites and subhedral augite, with or without glass. Hornblende, spinel, and calcite are accessories, and analcite fills vesicles. Corundum and mullite occur at the margins of kyanite grains.

The glass in the secondary assemblage has a composition roughly equivalent to what one might expect if it was derived by incongruent melting of omphacite, followed by partial crystallization. Omphacite at one atmosphere pressure begins to melt at about 1030? C and melting is complete at about 1260? C. At 30 kilobars (O'Hara and Yoder, 1967) melting begins at about 1570? C and is complete at 1600? C. Thus, sudden pressure release of an eclogite at high temperature could cause partial melting of omphacite.

These kyanite eclogites clearly contained an interstitial melt that has been rapidly cooled. Evidence points to this melt having been generated mainly by partial melting of primary omphacite rather than by introduction of an externally derived melt. The partial melting may have occurred in response to one of the following three processes or some combination of them:

  • Increase in temperature at constant pressure.
  • Introduction of water into the eclogite at constant temperature and constant total pressure.
  • Release of pressure at constant temperature.

The third process seems to offer the most reasonable explanation for the partial melting.

The Port Orford, Oregon, Meteorite Mystery
Roy S. Clarke, Jr., editor
43 pages, 19 figures, 7 tables
1993 (Date of Issue: 4 January 1993)
Number 31, Smithsonian Contributions to the Earth Sciences
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The Port Orford meteorite was allegedly discovered by John Evans, a contract explorer for the United States Government, on a mountain in southwestern Oregon in 1856. Efforts to organize the recovery of the alleged 10-ton body for placement in the Smithsonian Institution in Washington, D.C., began in late 1859, but were abandoned as a consequence of the simultaneous onset of the Civil War and Evans' death.

Early in this century journalistic reports revived the story and stimulated numerous unsuccessful amateur meteorite hunting expeditions into the inaccessible Siskiyou National Forest. Smithsonian investigators visited the vaguely defined site without success in 1929 and 1939. As time passed, it became increasingly obvious to some involved officials that there was something wrong with the original accounts. Nevertheless, most persons persisted in their belief that Evans' story was true.

This monograph combines an historical study by Howard Plotkin ("John Evans and the Port Orford Meteorite Hoax," pages 1-24), and a technical study by V.F. Buchwald and Roy S. Clarke, Jr. ("A Mystery Solved: The Port Orford Meteorite is an Imilac Specimen," pages 25-43).

In the first paper, Plotkin details the history of the mysterious lost Port Orford meteorite, and presents previously unreported evidence that indicates Evans was ill-trained for his scientific field work, which was superfically and unprofessionally executed, and that he had amassed a staggering personal debt by consistently overspending his budget. Most startling of all, Plotkin's research led him to the inescapable conclusion that Evans had acquired a small but very rare piece of meteorite, and had hatched a clever scheme whereby he could use it to turn around his financial affairs. Plotkin reconstructs in detail how Evans planned to carry out this hoax.

Finally, Plotkin endeavors to establish the true identity of the meteoritic sample. On the basis of its overall physical appearance, degree of weathering, and chemical composition, Plotkin argues that the Port Orford specimen is a fragment of Imilac, a Chilean pallasite discovered in 1820-1822. He further contends that Evans acquired it from someone else while crossing the Isthmus of Panama on his final return trip from Oregon during the fall of 1858.

In the second paper, Buchwald and Clarke describe the involvement of the National Museum of Natural History in attempts during this century to recover the meteorite, and they report on their detailed technical studies of the Port Orford specimen and other possibly related meteorites.

Buchwald and Clarke point out that only three distinct pallasite falls were known in the late 1850s: (1) the single Krasnojarsk, Siberia, mass, (2) the two large masses of the Brahin, Belorussiya, meteorite, and (3) the Imilac, Chile, shower. Both Krasnojarsk and Brahin were ruled out of a possible hoax scenario on the basis of physical properties and state of corrosion, which left Imilac as the only possibility short of invoking an otherwise completely unknown fall. They therefore undertook detailed metallographic and mineralogical examinations of the Port Orford specimen and several Imilac specimens in an attempt to resolve the matter.

They find that the Port Orford specimen is a main group pallasite that is chemically, structurally, and morphologically indistinguishable from Imilac. The steep thermal gradient of its heat-altered zone shows it to be an individual from a shower-producing fall and that it could not have been a specimen removed from a large mass. Its weathering history suggests the arid conditions of the high desert of Chile, not the humid Oregon coast forests. Port Orford's kamacite composition and hardness, olivine composition, trace element levels in metal, and shock levels in kamacite and troilite are all within observed ranges for the Imilac shower or within reasonable extensions thereof. These many congruencies led Buchwald and Clarke to conclude that the Port Orford meteorite is an Imilac specimen, and that Evans perpetrated a deliberate hoax using a small Imilac individual as bait.

Sands in the Alboran Sea: A Model of Input in a Deep Marine Basin
Daniel Jean Stanley, Gilbert Kelling, Juan-Antonio Vera and Harrison Sheng
51 pages, 23 figures, 8 tables
1975 (Date of Issue: 16 June 1975)
Number 15, Smithsonian Contributions to the Earth Sciences
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The Alboran Sea, an almost totally land-enclosed, mountain-bounded (Rif, Betic ranges) basin, lies east of Gilbraltar in the westernmost Mediterranean. A petrologic study of the sand fraction in river, river mouth, and beach samples collected on the coast of the Alboran Sea defines the composition and distribution of the principal light and heavy mineral groups along its margins. The investigation details 20 mineralogical provinces on the southern Iberian and northern Moroccan margins and the Strait of Gibraltar sector and identifies the major source terrains and fluvial and marine point sources of terrigenous sediment entering the basin.

Significant sample-to-sample changes in the proportion of mineralogical components are attributed to marine processes, particularly nearshore currents, which move sands laterally along the coast and, while so doing, modify the proportions of light and heavy mineral components. Lateral trends observed within Moroccan and Spanish mineralogical provinces provide evidence on the actual sense of nearshore sediment dispersal. Marine transport agents have a more pronounced effect on the light mineral fraction, while even unstable heavy mineral species appear to suffer less modification as a result of the transport in the marine environment. The paths followed by the sands between source terrain and final depositional site in deepwater environments are complex ones. A comparison of mineral assemblages in coastal sands and in sands in deep-sea cores shows a provenance from the Serran?a de Ronda complex in the Betic range west of M?laga. After initial deposition on the coast, these river-borne sediments are transported in a southwestward direction toward Gibraltar and then eventually are funneled downslope in a southeastward direction toward the Western Alboran Basin through the Gibraltar Canyon and submarine valley.

In geological terms, the Alboran. Sea study can serve as a model for sedimentation in one type of elongate enclosed basin bounded by regions of high relief. Although the geographic and geologic configuration of the Alboran Sea and contiguous land conforms to a multisource basin model, the transport paths of sediment since the late Quaternary have been essentially longitudinal. This longitudinal input, with filling as a result of currents primarily from the Strait of Gibraltar sector, is independent of a major delta source and is thus unlike many elongate, deep-sea basins examined in present oceans and troughs (including flysch) mapped in the ancient rock record.

Displaying 21 - 30 from the 33 total records